Quick viewing(Text Mode)

Corneal Anatomy

Corneal Anatomy

FFCCF! • Mantis Shrimp have 16 cone types- we have three- essentially and receptors. Whereas a has 2, a butterfly has 5, the Mantis Shrimp may well see the most of any animal on earth. Functional Morphology of the

Christopher J Murphy DVM, PhD, DACVO Schools of Medicine & Veterinary Medicine University of California, Davis

With integrated FFCCFs Why Does Knowing the Functional Morphology Matter? • The diagnosis of ocular disease relies predominantly on physical findings by the clinician (maybe more than any other specialty) • The tools we routinely employ to examine the eye of patients provide us with the ability to resolve fine anatomic detail • Advanced imaging tools such as optical coherence tomography (OCT) provide very fine resolution of structures in the living patient using non invasive techniques and are becoming

widespread in application http://dogtime.com/trending/17524-organization-to-provide-free-eye-exams-to-service- • The basis of any diagnosis of “abnormal” is animals-in-may rooted in absolute confidence of owning the knowledge of “normal”. • If you don’t “own” the knowledge of the terminology and normal functional morphology of the eye you will not be able to adequately describe your findings Why Does Knowing the Functional Morphology Matter? • The diagnosis of ocular disease relies predominantly on physical findings by the clinician (maybe more than any other specialty) • The tools we routinely employ to examine the eye of patients provide us with the ability to resolve fine anatomic detail http://www.vet.upenn.edu/about/press-room/press-releases/article/ • Advanced imaging tools such as optical penn-vet-ophthalmologists-offer-free-eye-exams-for-service- coherence tomography (OCT) provide very fine resolution of structures in the living patient using non invasive techniques and are becoming widespread in application • The basis of any diagnosis of “abnormal” is

rooted in absolute confidence of owning the http://aibolita.com/eye-diseases/37593-direct-ophthalmoscopy.html knowledge of “normal”. • If you don’t “own” the knowledge of the terminology and normal functional morphology of the eye you will not be able to adequately describe your findings

http://www.exam-vision.com/our-products/loupes.php Why Does Knowing the Functional Morphology Matter? • The diagnosis of ocular disease relies predominantly on physical findings by the clinician (maybe more than any other specialty) • The tools we routinely employ to examine the eye of patients provide us with the ability to resolve fine anatomic detail • Advanced imaging tools such as optical coherence tomography (OCT) provide very fine resolution of structures in the living patient using non invasive techniques and are becoming widespread in application • The basis of any diagnosis of “abnormal” is rooted in absolute confidence of owning the knowledge of “normal”. http://www.drquan.ca/retinal_OCT.html • If you don’t “own” the knowledge of the terminology and normal functional morphology of the eye you will not be able to adequately describe your findings Why Does Knowing the Functional Morphology Matter? • The diagnosis of ocular disease relies predominantly on physical findings by the clinician (maybe more than any other specialty) • The tools we routinely employ to examine the eye of patients provide us with the ability to resolve fine anatomic detail • Advanced imaging tools such as optical coherence tomography (OCT) provide very fine resolution of structures in the living patient using non invasive techniques and are becoming widespread in application • The basis of any diagnosis of “abnormal” is rooted in absolute confidence of owning the knowledge of “normal”. • If you don’t “own” the knowledge of the terminology and normal functional morphology of the eye you will not be able to adequately describe your findings Why Does Knowing the Functional Morphology Matter? • The diagnosis of ocular disease relies predominantly on physical findings by the clinician (maybe more than any other specialty) • The tools we routinely employ to examine the eye of patients provide us with the ability to resolve fine anatomic detail • Advanced imaging tools such as optical coherence tomography (OCT) provide very fine resolution of structures in the living patient using non invasive techniques and are becoming widespread in application • The basis of any diagnosis of “abnormal” is rooted in absolute confidence of owning the knowledge of “normal”. • If you don’t “own” the knowledge of the terminology and normal functional morphology of the eye you will not be able to adequately describe your findings https://www.google.com/search? q=writing+a+veterinary+medical+record&client=safari&biw=1200&bih=617&source =lnms&tbm=isch&sa=X&ved=0ahUKEwj6t5KWoKXLAhUH2mMKHZHrCioQ_AU IBigB#tbm=isch&q=veterinarian+writing+medical+record&imgrc=TywEW427rVhql M%3A Bottom Line If you don’t “own” the knowledge of the terminology and normal functional morphology of the eye you will not be able to adequately describe your findings in your records or to another clinician and you will not be prepared to adequately diagnose and treat patients with ocular disease.

Keep your eye on the prize…..This isn’t anatomy for anatomy’s sake, it’s an absolute requirement for you to be a competent clinician. Learning Objectives: Eye As A Whole

• To “own” knowledge of the functional morphology of the vertebrate eye – Basic design of “Joe” vertebrate eye and essential (additive) variations between vertebrate classes – Appreciate the wide variation in shape, size and relative dimensions of the ocular structures and spaces – Know the landmarks and terminology routinely used for spatial location of ocular structures and lesions Comparative

Crocodile fish 30,100 spp. 5,699 spp.

10,000 8,163 spp. Spp.

10 Mammals: 4,629 species

RR Dubielzig:OSOD 11 Though fascinating, we won’t be discussing the beautiful designs and wide variation in ocular structure found in invertebrates

http://www.eyedesignbook.com/ch3/eyech3-b.html

www.pbrc.hawaii.edu/bemf/ microangela/solar.htm www.pbs.org/wgbh/nova/leopards/ cuttlefish.html Joe Vertebrate Eye

The image cannot be displayed. Your computer may not have enough memory to open the image, or the image may have been corrupted. Restart your computer, and then open the file again. If the red x still appears, you may have to delete the image and then insert it again. Landmarks of the Vertebrate Eye

Note that a visual axis is present only for animals that have a discrete area of high cone (and thus high resolution) typified by the fovea of humans, other , lizards and or an area centralis such is found in dogs and . Also, a true canal of Schlemm is found in humans, primates, and birds. Domestic animals have a corneoscleral venous plexus a.k.a. an angular aqueous plexus (i.e not a single continuous channel that is a characteristic of Schlemm’s canal). All Adhere to the Basic Plan All Variations are Additive Fish fish • flat • ± pigment in cornea • scleral cartilage • ± scleral ossicles (nasal and temporal) • ± choroidal gland (pseudobranch www.pacificislandbooks.com/stufdwnld.html dependent) • spherical • annular ligament • retractor ()/protractor () lentis muscles • falciform process • avascular with retinomotor

movement www.optiquatics.com/…/pages/M2.%20Bob%20Stewart.%20fish (frogs, salamanders, caecilians)

• water-air transitions (lids & nictitans develop on metamorphosis) • usually cartilage in • wide range of shapes • ± oil droplets in cones of avascular retina

http://www.mascarino.com/RedEyeLeafFrogs.html Reptiles (crocodilia, chelonia, ophidia, lacerta)

• scleral ossicles & cartilage cup (not ) • striated muscle in and • ± annular lens pad • ± conus papillaris • avascular retina

zoltantakacs.com/zt/ pw/sn/s06.shtml Birds

• scleral ossicles & cartilage • annular pad • striated iridal and ciliary muscles • pteridine and lipidoidal iris pigments • fuse to lens capsule • corneal and lenticular accomodative mechanisms • • avascular retina Mammals

• smooth muscle in iris and ciliary body • lens suspended by zonules

• lenticular • only group with “true” retinal vessels Eye Size & Volume: Wide Variation

Cynomolgus Adult Mouse Rat Rabbit Dog Pig** monkey Human

Mean axial globe length (mm)* 3.2 6.27 16.83 19.96 20.65 23.9 17.58 23.6

*With the exception of the pig, means are calculated from literature values derived via in vivo methodologies. **Mean calculated from literature values derived via ex vivo methodologies.

Comparative Ocular Volumes By Species Cynomolgus Adult Mouse Rat Rabbit Cat Dog Pig monkey Human Mean anterior chamber (AC) 6 13 229 837 381 300 98 181 volume (µl)* Mean lens volume (ml)** 0.005 0.043 0.473 0.5 0.5 0.502 0.125 0.155† Mean (VC) 0.0053‡ 0.057† 1.153‡ 2.533† 2.65‡ 2.89‡ 1.9† 4.85‡ volume (ml)

* All means for AC volume are calculated from literature values derived via in vivo methodologies.

** Unless otherwise specified, all means for lens volume are calculated from literature values derived via ex vivo methodologies or geometric calculation.

† Mean derived from literature values derived via in vivo methodologies. ‡ Mean derived from literature values derived via ex vivo methodologies or geometric calculation. And………………. Eye Size: Affects (smaller the eye the more the mag)

Murphy CJ, Howland HC, The optics of comparative . Vision Res. 1987;27(4):599-607. and Head of the Sparrow (from Slonaker) Eye Shape

• Nearly spherical to tubular Great Horned

Calf

Horizontal limbal diameter > vertical

In birds, the shape of the eye is determined by the shape and extent of the scleral ossicles Superior vs Inferior = Dorsal vs Ventral

http://www.fci-ophthalmics.com/blog/symptoms-of-dry-eyes-and-their-causes/

Nasal vs Temporal Anterior vs Posterior = Front vs Back

Great Horned Owl (Bubo virginianus) Internal vs External Today’s Tour

• Three tunics (from external to internal are: fibrous/vascular/neural) – We will travel: • External to Internal – Anterior to Posterior • Internal Optical Media (lens & vitreous) Learning Objectives: Outer Fibrous coat and tear film

– Origin and importance of the tear film – Basic structure of the cornea and anatomic requirements for transparency – Architecture of the limbus and importance to ocular surface health – Structure of the sclera and lamina cribrosa Fibrous Coat

• Cornea and sclera • Transition occurs at the limbus (L. “edge”) • Most powerful optical element of the eye is the cornea (where the greatest change in occurs) • Protection • Determines shape of globe • Site of insertion of EOMs • and vessels pass through it Corneal Anatomy

www.snopes.com/horrors/ techno/cornea.htm http://www.allaboutvision.com/conditions/corneal-crosslinking.htm Corneal Anatomy

• Anterior : stratified squamous non-keratinized. • Bowman’s layer: collagenous acellular zone. Absent in all domestic mammals. Most variable element across vertebrates (present in birds, most primates, lizards, elephant, not present in domestic mammals) • Stroma: Lamellae composed of fine, uniform diameter, evenly spaced, fibrils • Descemet’s membrane (posterior limiting lamina): Robust basement membrane of posterior • Endothelium (posterior ): simple cuboidal epithelium Corneal Transparency

• The hallmark of corneal disease is an opacity • It’s transparent because of – What it has • Relatively dehydrated state (deturgescence) • Small uniform diameter collagen fibrils – Evenly spaced – Arranged in lamellae – And what it doesn’t have • Blood vessels • Myelinated fibers • Pigment Poetry and the Cornea Dearest Cornea What wondrous things are here to hold, the world’s beauteous The trees, the air, the singing birds, the starry sky of night Dear Hamlet, let me ease your mind, the answer is ‘‘to be’’ To use your , yes all five, but most important, see These mirrors to the soul sublime, reflecting earth and skies We raise our voices praising loud the wonder of the eyes Their composition provokes awe, the , optic nerves But let me sing of eyes’ true god, no less than it deserves I speak of crystal cornea, it’s nature satisfied Nonkeratinized coating of a skin that’s stratified Now if you dare, explore below, for underneath this phase Exists a structure so profound, it truly will amaze Oh stroma, central resident in eyeball’s prefecture There is perfection in your frame, a sanctified structure Lamellae lay apposed as close as soul mates e’er could be They’re packed together, tightly knit, transparent family And in each ply the fibrils run, parallel and long The web of collagen they make is precious yet it’s strong Each little bit of tissue spaced in perfect symmetry Is what allows the light to pass, it’s how we all can see But such grand things, they cannot last, lest they be mundane This stroma has its limit called by ‘‘Descemet’s membrane’’ Oh basement of the living , unique among your kind Your constitution is not matched, it’s pure and it’s refined The clarity is kept intact by keeping out the damp There’s little simple to the cubes, these cells defend the camp Jenna Buley For stroma clouds when moisture finds its way into each ply School of Veterinary Medicine, University of Wisconsin–Madison, So endothelium keeps guard, it keeps the stroma dry Madison, WI, USA The wonders do not cease right here, the glory the perfection Reproduced with permission: Jenna Buley, The innervation, substance P, the stunning fibronectin Dearest Cornea, CORNEA, Volume 27, Issue 9, Pg 975. There are not words to fully praise, try though as I might The cornea, the window live, that lets us see the light. Human// : 5 layers

E anatomy.iupui.edu/courses/histo_D502/ Lab.19.eye.f01.html AE BM (ALL) S DM (PLL) AE = Anterior epithelium BM = Bowman’s membrane or Anterior Limiting Lamina (acellular) S = Stroma (with intersperced keratocytes) DM = Descemet’s membrane or Posterior Liming Lamina E = Endothelium www.vetmed.ucdavis.edu/.../ epath_overview_index.html Domestic Mammals: 4 layers No Bowman’s Layer Bonus Time!!!

• What is the ~ central corneal thickness of the average adult human, dog, rabbit, rat?

Answers* Human: ~536 μm Dog: ~562 μm Rabbit: ~381μm Rat: ~159μm

* Values from single reports. Small ranges around these values reported in the literature and affected by age, breed & measurement technique Human- Doughty MJ, Zaman ML. Surv Ophthalmol. 2000 Mar-Apr;44(5):367-408. Dog- Gilger BC, Whitley RD, McLaughlin SA, Drane JW. Am J Vet Res. 1991 Oct;52(10):1570-2. Rabbit- Li HF, Petroll WM, Moller-Pedersen T, Maurer JK, Cavanaugh HD, Jester. Curr Eye Res. 1997 Mar;16(3):214-21. Rat- Schulz D, Iliev ME, Frueh BE, Goldblum D. Vision Research. 2003. 43: 723-728. Anterior Epithelium

• Single layer of Basal Cells • 2-8 layers of polygonal wing cells • 2-4 layers of superficial squamous cells

• Approx 10% of entire corneal : thickness. Masson‘s trichrome • Regularly replenished from limbus (its where the stem cells are!)

Thoft RA, Friend J. The X, Y, Z hypothesis of corneal epithelial maintenance. Invest Ophthalmol Vis Sci. 1983;24:1442–1443. If you got real small and looked at your feet while standing here………

Dog: H & E

Identify the single layer of basal cells. Note also the polygonal wing cells and the superficial squamous cells The most superficial cells of the anterior corneal epithelium are characterized by possessing microplicae and microvilli.

Name one function these could play? Continual Loss of Superficial Squamous Cells

http://80.36.73.149/almacen/medicina/oftalmologia/enciclopedias/duane/graphics/ figures/v7/0080/004f.jpg

Left: SEM of multiple superficial squamous cells of the anterior corneal epithelium Right: TEM of a single squamous cell of the anterior corneal epithelium sloughing off the surface into the precorneal tear film.. Where will it go? Corneal Epithelial Barrier Function (and how the clinician evaluates it’s integrity)

The intact anterior epithelium prevents access of the water soluble dye fluorescein to the the water contained in the of the stroma.

Rat cornea with intact anterior corneal epithelium after application of fluorescein: no fluorescein enters stroma Rat cornea with break in epithelium Images courtesy of Dr. Roy Bellhorn

Applying fluorescein Retention of the green stain to the cornea of fluorescein dye after rinsing a canine patient indicates a complete defect in the corneal epithelium (i.e. a region where epithelial cells are absent) Corneal Innervation: It does more than just transmit nociception:

• One of the most densely innervated structures in the body • Anterior aspect is innervated, posterior aspect devoid of nerves. • Neuropeptides – SP, CGRP, VIP • Neurotransmitters – Norepi & Ach

Rozsa, A. J. and Beuerman, R. W. (1982). Density and organization of free nerve endings in the corneal epithelium of the rabbit. Pain 14: 105-120. These compounds, secreted by the nerve endings, are trophic (neurotrophic). They are essential for maintaining normal corneal health If you denervate the cornea, degenerative changes will occur! Anterior Corneal Basement Membrane Chemical (e.g. Arginine-Glycine-Aspartate or RGD) and biophysical attributes (stiffness, topography) modulate a wide array of fundamental cell behaviors

The basement membrane has TEM Canine Anterior Corneal submicron and nanoscale topographic Basement Membrane features that influence cell behaviors Bowman’s Layer (Anterior Limiting Lamina)

http://www.lasik.md/learnaboutlasik/epilasik.php#.Vpyt_dC7VUs Warwick R (Ed) .1976. Eugene Wolff’s Anattomy of the Eye and . 7th Ed. (Fig 27)

• Found in humans, primates, birds, elephants & cetaceans (not in rodents, rabbits, pigs, dogs) • Acellular ~ 8- 12 μm thick • Specialized extracellular matrix • Lack of consensus as to function (mechanical role likely, protect subepithelial basal nerve plexus & underlying stroma? barrier functions?) • Non-regenerative (removed in superficial keratectomy as well as photorefractive and phototherapeutic keratectomy) Corneal Stroma – Substantia Propria

•80 – 90% of entire thickness •Extracellular fibers –Collagen, elastin •Collagen fibrils arranged in lamellae •Proteoglycans •Cells –Fixed –Wandering Keratocytes Interact with Each other Throughout the Stromal Thickness

Nishida: http://iovs.arvojournals.org/pdfaccess.ashx?url=/data/journals/iovs/933370/ Human Stromal Architecture

.Winkler M, Chai D, Kriling S, Nien CJ, Brown DJ, Jester B, Juhasz T, Jester JV. Invest Ophthalmol Vis Sci. 2011 Nov 11;52(12):8818-27. Corneal 3D Stromal Architecture Varies

Rabbit Human

Thomasy SM, Raghunathan VK, Winkler M, Reilly CM, Sadeli AR, Russell P, Jester JV, Murphy CJ. Acta Biomater. 2014 Feb;10(2):785-91.

Winkler M, Shoa G, Tran ST, Xie Y, Thomasy S, Raghunathan VK, Murphy C, Brown DJ, Jester JV. Invest Ophthalmol Vis Sci. 2015 Apr;56(4):2764-72. Lamellar Structure of the Normal Dog Cornea M Winkler, CJ Murphy,J Jester; : 2nd harmonic imaging (unpublished) Lamellar Architecture of the Corneal Stroma

TEM of the corneal stroma. Note the collagen fibrils within individual lamellae. The fibrils are uniform small diameter and evenly spaced. There are about 200 lamellae within the stroma. The ocular surgeon can exploit this architecture, cleaving between lamellae in performing a superficial keratectomy. Cross section of collagen fibrils within a single lamella. Note the uniform size and spacing. These are characteristics absolutely required for corneal transparency.

Normal K9 eye Corneal Edema: With inbibition of water, the stroma swells disrupting the even spacing of the collagen fibrils. In this case light is scattered and reflected resulting in the detection of a by the clinician

2 y old dog with diffuse corneal edema secondary to Descemet’s membrane = Posterior limiting lamina = Posterior limiting membrane (PLM) of the cornea = Basement membrane

Endothelium or posterior epithelium

Descemet’s membrane or PLM

Posterior stroma serves both barrier and active pump functions to minimize water content of the stroma.

FFCCF: Why do the corneal endothelial cells have a hexagonal outline? SEM of corneal endothelium that lines the innermost surface of the cornea Corneal endothelium: a simple cuboidal epithelium. The innermost layer of the cornea. In contact with the aqueous humor of the anterior chamber.

Bonus round: What does “simple” mean when used to describe an epithelial tissue? Hexagonal Double bonus round: What other structuresgeometries in natureare among the most are packed in hexagonal arrays and why?efficient packing geometries in nature The endothelial cells pump ions (and associated water) out of the cornea and contribute most heavily to the relatively dehydrated state of the stroma. The epithelial cells also contribute but to a lesser degree (and primarily by providing a barrier for access of the precorneal tear film). From Birth to Death: It’s a constant loss of cells

Very poor regenerative capacity in most species (rabbit an exception) cornea The Limbus: the zone of transition where cornea becomes continuous with the sclera and the anterior corneal epithelium becomes continuous with the conjunctival epithelium.

Polarizing light photomicrograph of the limbal

episclera region of a dog. The limbal region is indicated between the arrows. Note that the sclera does not

sclera possess a lamellar architecture. Also note that the stroma of the and the episclera is more loosely arranged (less compact). The episclera lies under the conjunctiva. Limbus: “Edge” Clinical Limbus

Sclera Cornea

http://medical-dictionary.thefreedictionary.com/_/viewer.aspx?path=dorland&name=limbus_corneae.jpg

•Corneoscleral transition zone (between arrows) •Contains vasculature (top right picture) •Can be pigmented •Common surgical landmark • Site of epithelial regeneration *Its where the stem cells are http://www.discoverymedicine.com/Johannes-Menzel-Severing/files/2011/01/ discovery_medicine_johannes_menzel-severing_no56_figure_1.gif Conjunctival Anatomy: Bulbar & Palpebral

Human Conjunctival Dog Fornix

http://student.vetdoctor.ru/ftp/wendy/data/ images/IM15000/IMC14976.gif

http://www.anatomyatlases.org/atlasofanatomy/plate31/images/31-20_static.jpg Dog

Bulbar and palpebral Fornices of 3rd FFCCF: What Does Fornix Mean?

Derived from Latin: ARCH Conjunctiva (Stratified columnar epithelium with loosely organized underlying stroma –we exploit the loose nature in creating conjunctival flaps to repair corneal defects)

Primate Eye: http://www.vetmed.vt.edu/education/curriculum/vm8304/lab_companion/histo-path/vm8054/labs/Lab11/Eye/EXAMPLES/EXCNJNCT.HTM

•Identify Palpebral conjunctiva/bulbar conjunctiva •What is another term for the “reflection point” in the figure on the left? •Identify the Goblet cells: What do they produce and what is the function of this substance? The Ocular Surface and the Tear Film

http://24.media.tumblr.com/tumblr_lveqgd3EvK1r42wsjo1_500.jpg

The Tear Film: Coats the Ocular Surface • Three distinct components – Outermost: (from Meibomian glands in lid margin) – Middle: aqueous (lacrimal and gland of 3rd eyelid) – Innermost: Mucin (from goblet cells of conjunctiva and cell associated

mucins) Meibomian glands in lids

Lacrimal gland and gland of 3rd eyelid

Goblet cells of conjunctiva and cell associated mucins Know the components of the tear film and where they come from!

Interfacial Phenomena and the Ocular Surface;Yañez-Soto, Bernardo et al. The Ocular Surface , Volume 12 , Issue 3 , 178 - 201 Glycocalyx

The membrane associated glycoprotein-polysaccharide constituents that extend outward from the most superficial cells of the cornea and conjunctiva. It plays a major role in determining the interactions of the tear film with the most superficial cells of the cornea and conjunctiva. Sclera

Characteristics •Dense irregular connective tissue •Weakly vascularized •No epithelial lining •Little innervation •Most internal aspect is typically pigmented (lamina fusca) Polarizing light photomicrograph of K9 sclera; contrast heterogeneity of collagen fiber size and organization with that of the cornea. Cornea

Compared to the cornea, the sclera has a denser more irregular architecture containing collagen fibrils of variable diameter that are randomly arranged. The Sclera sclera also has a higher water content and is weakly vascularized. Lamina Cribrosa: the scleral “sieve-like” structure through which the passes

http://dx.doi.org/10.1016/S1569-2590(05)10013-5 Figure 4 Scanning electron microscopy of collagenous fabirc of the human lamina cribrosa with the retinal (A) and vein (V) in the center. Circular arrangements of the collagen fibrils surround the openings for the passage of axons. May play a role in the pathogenesis of glaucoma (accentuate damage to nerves and blood vessels constrained in their passage through this area as a result of increased ) FFCCF! Three strategies amphibious animals have for dealing with the refractive loss of the cornea upon submersion in water

• Flat cornea (don’t matter)

• Massive lenticular accommodative range

• Don’t care: far sighted farschmighted: Scleral Ossicles: Non mammalian

Swordfish

Screech Owl Scleral Cartilage (it’s part of the eye) •Fish •Amphibia •Reptiles (except snakes) •Birds

•Monotremes ( & echidna) Review

www.vetmed.ucdavis.edu/courses/ vet_eyes/eye_p... Learning Objectives: Middle Vascular Coat

• Structures of the middle vascular coat and what are their functions • iris • ciliary body •

• Tapeta: who’s got them?, how are they built? What is their function?

• Aqueous production and outflow pathways and why important • Classical • Uveoscleral Iridocorneal Angle

Eagle Owl

www.stlukeseye.com/ anatomy/Iris.asp

A regional term that includes the peripheral internal aspect of the cornea, the outer surface of the root of the iris, the inner anterior aspect of the sclera & the trabeculae of the pectinate ligament and the that spans this region. Aqueous humor drains through this region to exit the eye through the corneoscleral venous plexus (also referred to as the aqueous angular plexusin domestic animals) and in primates and rodents as Schlemm’s canal. Sc Tr UvealS T Uveal Iris Juxtacanalicularhl abC IrisJuxtacanalicularc rC e eco hl ao m ulr e br m arn m ecn e e ’s M m ul C o ’s o an ess C as al hcl a r c we n Ml orr al ese kal hr wa ol r k

Iridocorneal Angle of the Primate (human)

Schlemm’s canal is a discrete aqueous outflow channel that encircles the angle. Found in man and other primates(and also attributed to rodents). Domestic mammals have an interconnected arborizing network of collecting channels referred to as the corneoscleral venous plexus that is synonymous with the angular aqueous plexus.

Trabecular Meshwork Trabecular Meshwork Trabecular Meshwork Uveal Uveal Uveal Schlemm’s Canal Schlemm’s Canal Schlemm’s Canal

Iris Iris Iris Juxtacanalicular Juxtacanalicular Juxtacanalicular

Corneoscleral Corneoscleral Corneoscleral SEM of Cat Iridocorneal Angle

Cut surface of Cornea ( line)

Inner surface of Cornea

Iridocorneal angle with trabeculae of pectinate ligament

Arrow indicates direction of fluid flow Anterior surface of iris that is folded down to allow imaging of angle Iridocorneal angle of the normal dog (as viewed through a goniolens)

Clinicians use a goniolens to overcome total internal reflectance and view the angle of the living eye http://upload.wikimedia.org/wikipedia/commons/thumb/7/7c/ Gonio.png/230px-Gonio.png

http://www.eyevet.ca/images/information/gonioscopy1.jpg

(gonio means angle) www.vetmed.ucdavis.edu/.../ epath_overview_index.html

CSVP

CSM

UM

Normal Dog Iridocorneal Angle (H&E stain): AC= anterior chamber; PL= Pectinate Ligament; UM= Uveal meshwork (of the trabecular meshwork); CSM= corneoscleral meshwork (of the trabecular meshwork), S= sclera; I= Iris Flow of Aqueous Humor

•Produced by ciliary processes of the ciliary body •Posterior chamber (space between front of lens and back of iris) •Anterior chamber •ICA & beyond •Traditional drainage pathway (AAP) •US – uveoscleral pathway (drains through C= cornea; AC= anterior chamber; PC= posterior chamber; ciliary muscles to gain aap= angular aqueous plexus (synonymous with corneoscleral venous plexus); US= uveoscleral pathway of aqueous drainage. access to suprachoroidal and supraciliary spaces) Corneoscleral venous plexus Classical Drainage pathway Ciliary processes Posterior chamber Pupil Anterior chamber Iridocorneal angle Trabecular meshwork Corneoscleral venous plexus (or Schlemm’s) Return to circulation

Uveoscleral Drainage Pathway Ciliary processes Posterior chamber Pupil Anterior chamber Iridocorneal angle through supraciliary/suprachoroidal space return to circulation

Species differences in uveoscleral flow as % of total outflow Humans 4-60% (indirect estimates, decreases with age) Cynomolgus 55 % Cat 3% WHY IT MATTERS Different drugs for the treatment of glaucoma act on Dog (beagle) 15 % different aspects of the production & drainage systems Rabbit (albino) 3-8% Mouse 66% (up to 80% reported) Aqueous Humor Dynamics

•Outflow = inflow (18 – 30 mm Hg among domestic spp) •Production mediated by: –Na/K ATPase pump –Carbonic anhydrase •Facility (outflow) mediated by: –Trabecular meshwork and CSVP (AAP) –Uveoscleral pathway (percolates through Ciliary musculature into supraciliary and suprachoroidal spaces) •Middle Vascular Coat: = Iris /Ciliary body/ Choroid • Modulates amount of light entering eye (pupil) • Accommodation (ciliary muscle and lens) • Suspend lens • Provide nourishment and remove waste for avascular lens and cornea • Nutrition to outer retina (or all of retina if avascular without accessory nutritional structures such as the avian pecten) • Tapetum in mammals • Maintain IOP and shape of globe • Pigment helps prevent light scatter (like black interior of a camera)

Uvea = Iris + Ciliary body + Choroid Irido = iris Cyclo = Ciliary Body Anterior Uvea = Iris + Ciliary body Canine Iris Margin

Pupillary Ruff: the axial extension of the posterior pigmented epithelium of the iris at the pupil margin (can see with )

Sphincter muscle fibers Heterochromia Iridis in a Cat

Bonus Round: What is the iris color of a true albino?

In mammals, iris are all derived from a single brown pigment () with the array of colors seen (blue to dark brown) arising from the differential interaction of light with melanin and the structure of the iris. Blue eyes have very little pigment while brown eyes have lots. Iridal Pigment: Non-Mammals

•Melanin •Carotenoids • Protein based pigments Ø Purines Ø Pteridines Canine Iris

Anterior Pupil Chamber

Posterior pigment of the the iris (borders the Myoepithelial dilator muscle of the the iris: posterior chamber, in contact with aqueous humor contracted by sympathetic stimulation-”wide eyed and moves across the anterior lens surface/ with fright” Canine Iris

Where is the Dilator Muscle of the Iris? & Non-mammalian Iridal Musculature

Iridal sphincter

•Skeletal –Amphibia Human iris: smooth muscle http://www.med.umich.edu/histology/cns/questions/ –Reptiles eyePract3.jpg –Birds

Striated Muscle •Skeletal and smooth Fibrs –Some reptiles and birds Pupillary Shapes Among Domestic Species Consist of 3 Basic Types

A = cats B = dogs, pigs, rabbits C = ungulates birdsofsanibel.free.fr/ new_page_4.htm

www.biol.lu.se/funkmorf/ vision/dan/pupil.html

Wide Variation in Pupil Shape Across Vertebrates zoltantakacs.com/zt/ pw/sn/s06.shtml Granula Iridica = Corpora Nigra: It’s an herbivore thing

What function might it serve? Granula Iridica = Corpora Nigra: It’s an herbivore thing

Granula iridica of the horse: the granula iridica serve as an intraocular eyeshade limiting light flux to the retina. It serves in a fashion similar to an awning over an outdoor café. It is generally better developed superiorly. Middle Vascular Coat: Ciliary Body

•Extends from root of iris (anteriorly) to ora ciliaris retinae (posteriorly). •Suspends lens (directly as in birds and through zonular fibers, most Ora ciliaris retinae species) •Produces aqueous humor •Decreases light scatter (due to presence of pigment) •Participates in accommodation (change in visual focus-ciliary muscles acting on changing lens curvature or location of lens along anterior-posterior axis) Ciliary Processes (of the )

•Site of blood-ocular barrier •Consists of fenestrated vessels, stroma, and double layered epithelium •Involved in aqueous humor production •Forms GAG component of vitreous humor.

http://parsplanitisforum.yuku.com/topic/40/Pars-planitis-anatomy-eye-photographs- definition-hotli#.VpzHJdC7VUs Ciliary Body

Back Surface of Iris The view from the photoreceptor’s perspective of the posterior surface of the iris and the internal surface of the ciliary body of the (left) and chicken eye (below). pupil

www.udel.edu/.../coloredempage/ coloredems.html Chicken

Ciliary body

Ora ciliaris retinae pupil Ciliary Process Microanatomy

•Bilayered epithelium –Inner •Nonpigmented –Outer •Pigmented •Stromal core contains capillaries and/or venules with fenestrated endothelium •Stroma –Loose connective tissue (view from the retina looking out)

•Variable in width •General widest dorsally and temporally

Intraocular surgical procedures are often performed by passing instruments through the pars plana (white arrows) to enter the eye. This area bleeds less than the pars plicata and the surgeon is less likely to damage the lens . The surgeon must know the landmarks and dimensions of this region in order to minimize complications upon entry into the eye. Aqueous Production at Level of Bilayered Epithelium

•Active formation by selective transport systems by: Carbonic anhydrase Na/K ATPase Sclera

Supraciliaris: Delicate stromal lamellae that span from the innermost layer of the sclera (lamina fusca) to the outermost layer of the ciliary body. The supraciliaris crosses the supraciliary space that is an important route for Ciliary body with ciliary aqueous drainage via the uveoscleral muscle fibers route. The supraciliary space is continuous posteriorly with the suprachoroidal space (located between the choroid and sclera) which is also part of the uveoscleral drainage pathway. Ora ciliaris retinae

Little brown bat (Myotis lucifigus) Middle Vascular Coat: Choroid •Extends from ora cilaris retinae posteriorly, external to retina

•Provide nourishment and remove waste from highly metabolic outer retina (all of retina if avascular retina without accessory nutritional structures such as avian pecten) Ora ciliaris retinae •Tapetum is a choroidal specialization found in superior fundus of all domestic mammalian species except pig and rabbit (absent in laboratory rodents).

Fundus: The portion of the interior of the eyeball around the •Pigment associated with choroid posterior pole, visible through the ophthalmoscope. Structures assessed during an evaluation of the fundus include the helps minimize intraocular light , retina, choroid and optic nerve head. scatter Choroidal Layers

•Provides nourishment to the highly metabolic outer retina (whole retina if avascular) •High blood flow •The tapetum (when present) is a specialization of the choroid in mammals

Photoreceptors

RPE •Choriocapillaris

•Medium and Large vessels •Suprachoroidea •The suprachoroidal space lies between the choroid and sclera and is spanned by Sclera http://www.iupui.edu/~anatd502/Labs.f04/eye%20lab/pages/s94_40x_15_jpg.htm the lace-like lamellae of the suprachoroidea Choriocapillaris: the capillary bed immediately subjacent to the RPE Between the RPE and tapetum (if tapetum present) or larger vessel layers (if tapetum absent) The (Brilliant Carpet)

• for seeing in dim light

•Terrestrial mammals: -superior -triangular in shape -base of triangle near optic nerve -it’s a choroidal adaptation (in mammals) -always located just external to choriocapillaris -two broad types: -cellular () -fibrous (herbivores) •Found in all domestic mammals except the pig (absent in rabbits and lab rodents) •Fish (e.g. walleye): can have associated with RPE www.news.cornell.edu/.../ gene_therapy_dogs.html Canine: Tapetal region. Note that in the region of the tapetum the RPE lacks pigment and penetrating vessels can be seen passing through the cellular tapetum serving as conduits to and from the choriocapillaris. On clinical ophthalmoscopic examination the penetrating vessels are often seen in cats and as evenly spaced dots and referred to as the “Stars of Winslow”

Neural Retina

RPE & Choriocapillaris

Cellular tapetum

Large vessel layer of choroid

Sclera with lamina fusca Canine: Nontapetal region. Note that in the region lacking a tapetum that both the RPE and choriocapillaris possess pigment.

www.news.cornell.edu/.../ gene_therapy_dogs.html

RPE & Choriocapillaris Tapetum Cellulosum: Functional unit is the tapetal rodlet

Rodlets with high levels of: •Zinc (cysteine) –Dog, Ferret •Riboflavin –Cat •Sulfur –Spotty cava, Paca

Animal Max Thickness (um) No. of Layers Dog (B) 43 5 – 8 (15) Cat (D) 87 12 – 15 (35) Cougar (A) 97 21 – 35 Ferret (C) 50 8 – 10 (12) Fibrous tapetum (FT in image) of ungulates. The tapetum lacks pigment.

E= RPE B= Bruch’s membrane (conjoined basement mebranes of the RPE and choriocapillaris) C- choriocapillaris of choroid FT = fibrous tapetum

Where do the colors of the tapetum arise (both cellular and fibrous tapeta)? They are structural colors (i.e. they are not caused by pigments but due to the differential interaction of light with the Optic structural elements of the tapetum. Nerve Normal equine fundus. Note tapetal coloration Bonus Round

Equine: What histologic differences would account for the difference in appearance of the fundus in region A vs region B ? (this is a normal variation) A B B In A, the reddish color is due to the lack of a fibrous tapetum. This along with the lack of pigment in the RPE enabled visualization of the choroidal vasculature. In B, the normal tapetal structure is present preventing visualization of the more externally located larger diameter choroidal vessels.

Remember though…… in both cases the choriocaplillaris is located immediately subjacent to the RPE-these very fine vessels are simply not Fundus refers to the back portion of the interior visualized by ophthalmoscopic exam. of the eyeball, visible through the pupil by use of the ophthalmoscope. It includes all structures that can be visualized. Can you name them? Non-tapetal Fundus

•Normal variation (dogs, cats, horses etc)

Fovea

•Primates Margin of optic nerve •Squirrels Lack a •Red Kangaroos tapetum •Pigs Pecten oculi

•Birds* Red Crowned Crane Accessory Nutritional Structures of the Fundus: Choroidal Gland of Fish (#6 in image to left)

aquaticpath.umd.edu/ fhm/eye.html Accessory Nutritional Structures of the Fundus: Conus papillaris of all lizards and other select reptiles

www.vetmed.ucdavis.edu/courses/ vet_eyes/eye_p... Accessory Nutritional Structures of the Fundus: Pecten Oculi of Birds

Great horned owl

Ora ciliaris retinae

Pecten oculi Red tail Golden eagle

The pecten is a highly vascular pigmented tissue that supplies nutrition to the avascular retina. Review Learning Objectives: Inner Neural Coat

• Retinal structure and function (be able to name and locate the cellular elements: RPE to optic nerve)

• Vascular patterns of the retina in mammals

• Accessory nutritional structures in non-mammalian vertebrates (e.g. avian pecten)

• Pathway of transmission of visual information from photoreceptor to brain

• Role of interneurons in retina Inner Neural Coat: The Retina Canine Retina

RPE

Photoreceptors

Interneurons

Ganglion cells

www.vetmed.ucdavis.edu/.../ epath_overview_index.html www.utdallas.edu/~tres/integ/ sen3/sense_3.html

www.nature.com/.../v2/n2/slideshow/ nrn0201_109a_F1.html Phagocytosis Slow nonspecific Rapid uptake of shed OS Recognition (OS bind to apical microvilli) Invagination (actin) Formation of phagosome Transport to basal lysosome (microtubule) Phagolysosome (lipofuscin if deficient) (nuclei of rods and cones)

External limiting membrane (outer limit of Muller cells)

Photoreceptor inner segment Notice the difference in morphology between rods and cones inner and outer segments

Photoreceptor outer segment

Retinal Pigmented Epithelium (RPE) The absorption spectra of the four photopigments in the normal human retina. The solid curves are for the three kinds of cone opsins, the dashed curve for rod rhodopsin. www.utdallas.edu/~tres/integ/ sen3/sense_3.html Red Eared Slider : flat mount (intraocular spectral filters)

Some species such as aquatic have oil droplets of differing colors located immediately in front of the outer segment of the cone photoreceptors. This alters the spectral composition of the light being presented to the photopigment in the photoreceptor. Some oil droplets are thought to serve as intraocular polarizing filters. Concept of Retinal Summation

The more summation (convergence as go from photreceptors to ganglion cells) the greater the light sensitivity (good for low light levels) and the worse the resolution (loss of fine detail). Least convergence in the fovea (best resolution, highest cone density. Cone:ganglion cell ratio approx. 1:1). Horizontal and Amacrine cells have numerous synaptic contacts and participate in the processing of visual information (the retina is an outgrowth of the brain)

webvision.med.utah.edu/ IPL.html webvision.med.utah.edu/ HC1.html Rabbit horizontal cell network revealed by dye injections. Muller Cell

• Principal non-neuronal cell of the retina • Defines – Outer Limiting Membrane – • Only one type • Many new functional functions being discovered-not just a structural role! • Forms inner (third) order of retinal neurons • Concentrated in number at the fovea/area centralis (sometimes 2-3 cell layers thick) • Axons from ganglion cells make up nerve fiber layer and when collected together form the optic nerve. Nerve Fiber Layer

• Axons (unmyelinated) of ganglion cells • Directed towards the optic nerve • Transmits signal to the visual centers of the CNS • Layer where larger vessels are housed in holangiotic retina Areas of Increased Retinal Acuity: Fovea, Area Centralis, Visual Streak

Fovea: an actual depression in the inner contour of the retinal surface (neural layers shifted to side). Increased concentration of cones, in mammals (having retinal vessels) sparce vascularization and avascular in center. Area of greatest resolution.

Fovea are common in primates, birds, lizards & fish Central and temporal fovea Diurnal birds of prey and select other avian of a hawk species can have two foveae in each retina Red tail Primate Fovea

www.utdallas.edu/~tres/integ/ sen3/sense_3.htm Rod and Cone Along the Human Retina (note the dramatic shift in the relative densities as you move outward from the fovea)

Fovea

www.utdallas.edu/~tres/integ/ sen3/sense_3.htm The center of the fovea is a vascular free zone

In the region of the fovea there is a decrease in retinal vessels with the center of the fovea being a vascular free zone Area centralis: an area of increased cone density without a change of the internal contour of the retina. Not as high a concentration of cones as in animals with a fovea. Dogs and cats. The cone density typically decreases along a horizontal band extending nasally from the area centralis

CJ Murphy, D Samuelson, RV Pollack. The Eye. In: Millers Anatomy of the Dog; 4th ed Area Centralis (Cat)

Fundus indicating location of X area centralis (X) temporal to the optic nerve head in a cat.

The distribution of retinal ganglion cells in the cat’s retina (left eye). Colors are used to indicate cell packing density. The area centralis (dark blue region) contains as many as 8,600 cells/mm2. Cell densities are particularly high along the horizontal axes from the temporal periphery (right) to the nasal periphery (left). Fovea-like Photoreceptor Array in Area Centralis of Dogs (though no pit)

Beltran, Cideceyan, Guziewicz et al. PLoS One. 2014 Mar 5;9(3):e90390. doi: 10.1371/journal.pone.0090390. eCollection 2014. Canine retina has a primate fovea-like bouquet of cone photoreceptors which is affected by inherited macular degenerations. . Visual Streak: A horizontally oriented linear zone of increased cone density that is found typically in prey species, Characteristic of the horse, cow, and pig. The shaded boxes in the images below approximate the location of the visual streak that passes horizontally both temporal and nasal to the optic nerve.

Cow Pig Retinal Vascular Patterns

Holangiotic (only mammals): many rodents, carnivores, artiodactyls, pigs

Merangiotic (only mammals): rabbits and hares

Paurangiotic (only mammals): perrisodactyls (horse), Guinea pig

Anangiotic: some mammals (e.g. porcupines) and all non- mammalian vertebrates Cat Fundus Holangiotic: Richly vascularized

www.biomedcentral.com/.../ 18/figure/F4?highres=y Mouse Fluorescein Angiogram

Cow Merangiotic (rabbit): vessels limited to extending horizontally out from the optic nerve following the myelinated medullary rays

Paurangiotic (horse): numerous small vessels that extend only a short distance from from the optic nerve. Gives the optic nerve head a “salmon colored flush” Anangiotic (fish, amphibians, reptiles, birds and some mammals)

Foveae

Pantadon (butterfly fish)

Pecten Falciform process, another accessory nutritional Right eye Red tail structure

www.crab.rutgers.edu/ ~saidel/saidel.html Optic Nerve

http://www.aapos.org/terms/conditions/83

http://www.glaucoma.org/research/optic-nerve- http://borg.ensc.sfu.ca/research/multimodal.html regeneration-1.php • Optic nerve head (disc, papilla) Optic Nerve elevated with physiologic cup • Bundles lined by pial elements • Pass through fibrous tunic, lamina cribrosa (LC) (mouse has a “cellular” lamina) • Axonal myelination post-LC, except dog. Degree of myelination in dogs is highly variable. • Axonal number (total number of axons which ultimately determines information carrying capacity) is species/strain variable

Optic Nerve Axon # Human: 770,000 - 1.7 million nerve fibers Cynomolgus: 770,000 - 1.7 million nerve fibers Rhesus: 1.5 million fibers Dog: 148,300 fibers Cat: 193,00 fibers Pig: 442, 629 fibers Rabbit (albino): 291,000 -394,000 fibers; (pigmented):250,000 – 270,000 fibers Rat (albino): >100,000; pigmented: 72,000 Mouse: 32,000 - 87,000 (strain variable)

Data from: May CA. Comparative Anatomy of the Optic Nerve Head and Inner Retina in Non-Primate Animal Models Used for Glaucoma Research. Open Ophthalmol J. 2008; 2: 94–101. Review Review

www.utdallas.edu/~tres/integ/ sen3/sense_3.html

www.nature.com/.../v2/n2/slideshow/ nrn0201_109a_F1.html Learning Objectives: Internal Optical Media

• Basic architecture of the lens and its capsule

• Species difference in lens shape and relative size

• Location of lens epithelial cells and role in lens growth

• Location and importance of lens epithelial bow zone

• Basic structure of vitreous

• Where vitreous is attached and why important Internal Optical Media: Aqueous, Lens, Vitreous Body Huge Variation in the Size of the Lens Relative to the Size of the Globe

Primate Mouse

Images coutesy Dr R Dubielzig: CORL

As it ages the optical properties of the lens are slightly altered with the nuclear material being denser than the more recently deposited cortical material. Discrete zones can be detected with slit lamp examination by the clinician. Mature Lens is Typically Divided Into:

•Capsule –anterior –posterior •Cortex –anterior –Posterior •Nucleus –embryonal –fetal –adult The anatomical details of the lens can be clearly imaged by the clinician using a slit lamp biomicroscope

Note the increased thickening of the lens with aging (it grows throughout life) and the alteration of the optical properties Anterior Lens Capsule Is Thicker Than The Posterior Lens Capsule At All Times and Increases In Thickness With Aging Lens Epithelial Cells: Limited to the anterior lens capsule and extend to the equatorial “ bow zone”. In the bow zone the epithelial cells elongate and become the lens fibers eventually losing their nucleus. The anterior and posterior junctions of the lens fibers form the sutures of the lens. The lens grows throughout life. Analagous to the growth of a tree, the oldest lens material is in the center (nucleus) with the newest material being located subjacent to the lens capsule. www.stlukeseye.com/ anatomy/Iris.asp

www.ralf-dahm.de/.../articles/ ma99/lens_drawing.html Lens sutures: It’s where the lens fibers meet (and where cataractous changes can be seen to develop)

Human lens with an anterior sutural Suture pattern in the dog: the anterior cortical sutures form an upright “Y” while the posterior sutures form an inverted “Y” pattern. This illustration is looking from the back towards the front of the lens. Lens

Lens Capsule

Hexagonal Lens Cortical Fibers

Where else have you seen this packing geometry???? Note packing of adjacent hexagonal lens fibers with ball and socket junctions Avian (& Lizard) Lens: Annular Pad

Annular pad is thought to act similar to the hands compressing balloon; evenly distributing the forces applied to the lens equatorisl cortex to bring about a change in lens curvature during visual accommodation In Mammals: Zonular Fibers Suspend the Lens

www.udel.edu/Biology/Wags/histopage/ empage/eey/eey.htm In Birds: Ciliary Processes Fuse to the Lens Capsule Assisting Zonular Fibers in Suspending the Lens Case: 2 week old owl presented for evaluation of . Bird seems to be doing ok but “them eyes sure look milky doc”.

“blue lenses” are a normal developmental phase in young raptors. It a developmental phenomenon and the lenses clear by 4-6 weeks of age. Accommodation in Mammals

www.utdallas.edu/~tres/integ/ sen3/sense_3.html

At rest the lens is held in a relatively flattened state by the intrinsic pressure exerted on the equatorial region via the ciliary body and transmitted through the zonules. Contraction of the ciliary muscle results in overcoming this tension allowing the lens to assume a more rounded contour as dictated by the intrinsic elastic properties of the lens capsule. This is characteristic of primates (including humans) It is possible that the dog, cat & horse accommodate via moving the lens closer to the cornea (axial translocation- proven for the racoon). Lenticular Accommodation

Contracted Relaxed Figure 3.36d Painted Wood Eyes, p 81 Reptiles & Amphibians http://www.biol.andrews.edu/everglades/organisms/Vertebrates/birds/bird_pages/cormorant_eye.jpg Cormorants and Aquatic Turtles lead amphibious lives. They compensate for the optical loss of the cornea in water by having extensive accommodative mechanisms. In these groups the iris sphincter actually deforms the anterior lens to achieve accommodative ranges that are much greater than terrestrial vertebrates. Vitreous Body: the single largest structure in the eye

The adult vitreous in mostly water and is transparent. It has hygroscopic glycoaminoglycans )GAGs) that are responsible for its gelatinous nature. It has a that accommodates the posterior surface of the lens. Lens The vitreous can be removed surgically without Vitreous impairment of vision. Cells that migrate into the vitreous associated with inflammation have a longer residence time than do cells that enter the aqueous humor. Vitreous Attachments (and why they’re relevant) The vitreous has firmest attachments to the vitreous base (strongest attachment) and to the region of the optic nerve head. There are also attachments to the posterior lens capsule and an increased attachment observed in humans along the peripheral retinal vessels and to the foveal region of the retina.

Why you should care: The vitreous base straddles the ora ciliaris retinae making this region sensitive to creating peripheral retinal pathology (detachments and/or ) as a result of frank trauma or in association with intraocular surgery. The attachments to the lens have to severed when removing the lens and its capsule in toto.

http://www.images.missionforvisionusa.org/anatomy/uploaded_images/VBMfV-742224.jpg http://www.oculist.net/downaton502/prof/ebook/duanes/pages/v3/ch027/001f.html The Vitreous Base (VB in illustration above) of the Human Eye: The vitreous Vitreous traction at the posterior aspect of the base extends anterior and posterior from the ora seratta (the proper term for the vitreous base predisposes to retinal breaks at this human rather than ora ciliaris retinae) . Arrows indicate ora seratta. The white location. Both flap tears (horseshoe tears) and tissue above the arrow points is fixed retina). operculated tears may occur. Final Review!!!!

Top View