Primary Eye Care Basics

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Asia Primary Care: Primary Eye Care Basics

Christopher Rugaber, OD, MSc, BS Version 10 October 2562

Anatomical Terms

Superior

Inferior

Posterior

Medial

Lateral

Proximal

Distal

Nasal

Temporal

Frontal, Coronal view / Frontal, Coronal plane / Frontal, Coronal section

Transverse view / Transverse plane / Transverse section

Saggital view / Saggital plane / Saggital section

Ipsilateral: Same side

Contralateral: Opposite side

Unilateral: One side

Bilateral: Both sides

Project / Project to: Travel / Travel to

Decussate: Cross to the other side

Superficial: Near the outer layer or outside

Deep: Near the inner layer or inside

Central: At the center

Paracentral: Near the center

Peripheral: Near the edge, away from the center

Apex / Base / Cone

Foramen: An opening, hole or passage, especially in a bone

Fissure: A long, narrow opening in the form of a crack or groove

Insertion / Iris insertion / Iris root: Where the iris attaches to the ciliary body

Aperature: An opening or entrance, for example, the palpebral aperature

Fossa: A shallow depression or hollow

Margin: The outside limit or edge of something

Limbus: Edge or border

Barrier: Something that prevents movement or access, blood-retinal barrier (RPE), blood-aqueous barrier

Punctum: Point, tip, opening of lacrimal duct

Papilla: A small projecting body part, like a nipple

Canal: A tubular passage or channel

Canaliculus: A small channel or duct

Duct: A tubular body canal or passage, especially for carrying a glandular secretion or tears

Secretion: Stuff that is produced, like saliva, mucus, tears or a hormone (noun). The process or act of releasing stuff like saliva, mucus, tears, or a hormone (verb).

Sac: A pouch or cavity, bag

Valve: A membrane fold or other structure that controls flow of fluid, for example allowing fluid to flow in one direction only

Disc: A round, flat anatomical structure

Cup: An excavation, หลุม

Macula: A small spot. On the skin a macula is a small flat spot. In the eye, it is a region of the retina.

Fascicle or Bundle: A group of objects held together. A nerve fascicle is a small group of axons bundled together

Ganglion: A structure containing a number of nerve cell bodies, often linked by synapses, and often forming a swelling on a nerve fiber

Eye Movements

ADduction: กลอกตาเข้าใน เข้ามาที่หัวตาก

ABduction: กลอกตาออกนอก ออกไปทางตา

Elevation: กลอกตาข้ึนบน

Depression: กลอกตาลงล่าง

Intorsion: หมุนตาเข้าใน ตาแหน่ง 12 นาฬิกา

Extorsion: หมุนตาออกนอก ตาแหน่ง 12 นาฬิกา

Esotropia, exotropia, hypertropia, hypotropia, esophoria, exophoria, hyperphoria, hypophoria

Comitant / concomitant strabismus

Noncomitant / incomitant strabismus

Convergence: Moving together

Divergence: Moving apart

Primary gaze: Position of eyes in binocular vision, when the head is erect and looking at an object at infinity

Six diagnostic or cardinal positions of gaze:

Fixation: Direction of gaze towards an object, usually so that the image of that object falls on the retinal macula or fovea

Central fixation: The image of the object being looked at falls on the retinal macula or fovea

Peripheral (non-central) fixation, eccentric fixation: The image of the object being looked at does not fall on the retinal macula or fovea

Other Terms

Blurred vision: Vision that is not clear

Visual field: The total area where objects can be seen while focusing on a central point

Visual field defect: An area of the visual field that is less sensitive (to seeing) than it normally should be

Quadrant / Hemi: Each of four parts of an object; retinal quadrant, visual field quadrant, quadrantopia, hemianopia (quadrantopsia = quadrantopia, hemianopsia = hemianopia)

OD: Right eye

OS: Left eye

OU: Both eyes

Test sensitivity: The ability of a test to find patients who have a condition…a test with high sensitivity has few false negatives

Here’s a crazy example of a test with high sensitivity…check every patient to see if they are alive…if they are alive, then they have glaucoma. This test will not miss finding any patient with glaucoma, so it has perfect sensitivity...zero false negatives

Test specificity: The ability of a test to show positive only for patients who really have a condition…a test with high specificity has few false positives

The crazy test will say that many people have glaucoma when they really don’t…it says 100% of people who are alive have glaucoma, when really only about 5% of people have glaucoma. So this test has very low specificity…it has many false positives

Diplopia / double vision

Fusion: The image of a single object projecting to or falling on the fovea of each eye (at the same time)

Paralysis or palsy: Complete lack of muscle function

Paresis: Weak muscle function

Anesthesia, paresthesia, hypoesthesia

Contract (muscle):

Extend or relax (muscle):

Ocular motility / Ocular motilities: Eye movement

Ocular motility deficit: Abnormal, or restricted (less than full, less than 100%) eye movement

Miosis: The act of the pupil becoming small

Miotic pupil: A small pupil

Mydriasis: The act of the pupil becoming big

Mydriatic pupil: A large pupil

Anisocoria: Pupil size OD different than the pupil size OS

Corectopia: Displacement of the pupil (from its normal central position), the pupil may be oval or slit-shaped

Heterochromia iridis: Iris color OD different than the iris color OS (see the photos folder)

Heterochromia iridum: An single iris having more than one color (see the photos folder)

Iridodialysis: Separation of the iris at its attachment to the ciliary body

Iridodonesis: Motion of the iris with eye movement. This may be caused by lens subluxation, or aphakia

Video: https://youtu.be/JxF5WMG7Qls

Lens subluxation: Partial dislocation of the lens

Lens luxation: Total dislocation of the lens

Synechia: An adhesion, especially an adhesion of the iris to other parts of the eye

Anterior synechia: An adhesion of the iris to the cornea or structures of the anterior chamber angle

Aphakia: Lack of a crystalline lens (no crystalline lens) / Aphake: A person with aphakia

Pseudophakia: Presence of a surgically implanted artificial crystalline lens, often after cataract surgery

Peudophake: A person with pseudophakia

Posterior synechia: An adhesion of the iris to the lens

Prolapse: A slipping forward or down of a body part

Iris prolapse: Iris tissue is outside of a corneal wound

Vitreous prolapse: Movement of vitreous into the anterior chamber

Injection / erythema: Abnormal redness due to capillary congestion (dilation or telangiectasia) Eyelid margin injection / erythema, conjunctival injection

Chemosis: Conjunctival swelling or edema

Icteric sclera / Icteric conjunctiva (due to a high blood bilirubin level)

Anesthesia: Reduced sensitivity to pain

Inflammation: A condition where a part of the body may become, red, hot, swollen, and often painful, especially as a reaction to infection or injury

Infection: The invasion and multiplication of organisms that usually aren’t in the body, such as bacteria, viruses, or parasites (fungi)

Edema: An excess of watery fluid collecting in tissues or cavities of the body

Ischemia: Inadequate blood supply to an organ or body part

Infarction: An area of tissue death caused by inadequate blood supply

Hypoxia: Inadequate oxygen supply to tissue

Retinal cotton wool spot: A lesion of the retinal nerve fiber layer, with edema and accumulation of axoplasmic material believed to be caused by ischemia from poor retinal arteriole flow.

Lesion: A region in tissue or a body part that has been damaged by injury or disease

Hemorrhage: Escape of blood from a vessel (pre-retinal hemorrhage, flame retinal hemorrhage, dot-blot retinal hemorrhage, sub-retinal hemorrhage)

Exudate: A fluid with a high content of protein and cellular debris that has escaped from a blood vessel and has been deposited in tissues or on tissue surfaces

Aneurysm: Localized enlargement of an artery caused by weakening of the artery wall

Retinal microaneurysm:

Bifurcation: Division into two parts

Anastomosis: A connection between two normally separate tubular structures, like blood vessels

Embolus: A blood clot, air bubble, piece of fatty deposit, or other object that has been carried in the bloodstream to lodge in a vessel and cause an embolism, often a piece of a thrombus. Intravenous drug users may have talc retinal emboli, because they grind up pills that have talc in them (like methyphenidate), mix it with saline, and then inject it into their veins.

Thrombus: A mass of platelets and/or fibrin that forms in a blood vessel (a clot)

Neovascularization: New vessels that are formed to supply blood to an area that isn’t getting enough blood, or is ischemic

Infiltrate: To penetrate (verb) Foreign substance that has penetrated (noun); a corneal infiltrate is white blood cells that have penetrated the cornea

Ulcer: A open lesion, with a break in the tissue surface that doesn’t heal; an open break in the corneal tissue may be an ulcer

Corneal endothelial polymegathism (differing cell sizes) and pleomorphism (differing cell shapes)

Precipitate: A substance deposited in solid form

Keratic precipitates: Inflammatory cellular deposit on the corneal endothelium

Flare: Scattering of light seen when a slit-lamp beam is directed, obliquely to the plane of the iris, into the anterior chamber. It occurs as a result of increased protein content, and usually inflammatory cells (in the aqueous humor). ... It is a sign of intraocular inflammation.

Anterior chamber with cells and flare Clear anterior chamber

Sebaceous: Relating to fat or oil

Suderiferous: Relating to sweat

Orifice: An opening of a pipe or tube, or a body opening such as a nostril

Abrasion: An area damaged by wearing or scraping away

Laceration: A wound (lesion) where the skin is cut or torn open

Contusion: A lesion where blood vessels are damaged or broken, allowing blood to seep or flow into the surrounding tissue (hematoma)

Ecchymosis: A flat lesion larger than 1 cm where blood vessels are damaged or broken, allowing blood to seep or flow into the surrounding tissue

Fracture: A break in bone or cartilage

Foreign body / corneal foreign body:

embed / embedded: ฝัง

Etiology: The cause, or causes of a disease or condition

Parasympatholytic: Something that reduces the activity of the parasympathetic system

Parasympathomimetic: Something that increases the activity of the parasympathetic system

Sympatholytic: Something that reduces the activity of the parasympathetic system

Sympathomimetic: Something that increases the activity of the sympathetic system

Lacrimation: The secretion of tears

Epiphora: Flow of tears onto the cheeks caused by lacrimal drainage system pathology

Ptosis: Drooping of the upper eyelid

Tylosis: Inflammation and thickening of the eyelid margins

Trichiasis: Misdirected eyelashes (towards the globe) with normal eyelid margins

Distichiasis: Two rows of eyelashes, perhaps growing from the meibomian gland orafices (definitions vary)

Ectropion: Eyelid margin turned away from the globe

Entropion: Eyelid margin turned towards the globe

Lagophthalmos: Incomplete closure of the eyelids

Poliosis: An area of white hair

Madarosis: Loss of eyelashes

Blepharitis: Inflammation of the eyelids

Conjunctivitis: Inflammation of the conjunctiva

Episcleritis: Inflammation of the episclera

Scleritis: Inflammation of the sclera

Keratitis: Inflammation of the cornea

Iritis: Inflammation primarily involving the iris

Anterior uveitis: Inflammation primarily involving the iris, or iris and ciliary body (definitions vary)

Iridocyclitis: Inflammation primarily involving the iris and ciliary body

Posterior uveitis: Inflammation primarily involving the choroid and retina

Retinitis: Inflammation of the retina

Phlebitis: Inflammation of the walls of a vein

Arteritis: Inflammation of the walls of an artery

Neuritis: Inflammation of a nerve

Preseptal / periorbital cellulitis: Infection anterior to the orbital septum

Orbital cellulitis: Infection of the orbital tissues posterior to the orbital septum

Some Cranial Nerve Functions

Nerve Name Function Result of Pathology to Nerve

CN II Optic Seeing Blurred vision, visual field defect

CN III Oculomotor Eye movements Double vision (diplopia)

Eyelid movement Ptosis

Focus, pupil movements blur at near, miotic or mydriatic pupil

CN IV Trochlear Eye movements Diplopia

CN V Trigeminal Sensory to face Anesthesia

CN VI Abducens Eye movements Diplopia

CN VII Facial Muscles of face Facial paralysis

CNVIII Auditory-vestibular Hearing and balance Problems with hearing/balance

Extra-ocular muscles (EOMS)

Superior rectus (controlled by CN III)

Inferior rectus (controlled by CN III)

Medial rectus (controlled by CN III)

Lateral rectus (controlled by CN VI)

Superior oblique (controlled by CN IV)

Inferior oblique (controlled by CN III), insertion on the maxillary bone

Rectus and superior oblique EOM insertion at the annulus of Zinn located at the orbital apex

EOM Actions in Primary Gaze (Straight Ahead) Superior Rectus Medial Rectus Inferior Rectus Primary: Elevation Primary: Adduction Primary: Depression Secondary: Intorsion Secondary: XXX Secondary: Extorsion Tertiary: Adduction Tertiary: Adduction

Inferior Oblique Lateral Rectus Superior Oblique Primary: Extorsion Primary: Abduction Primary: Intorsion Secondary: Elevation Secondary: XXX Secondary: Depression Tertiary: Abduction Tertiary: Abduction Primary action WITH ADDUCTION: Depression

SUPERIOR MUSCLES INTORT RECTUS MUSCLES ADDUCT (LR)

THE HYPER EYE SEES THE LOWER IMAGE

CROSSED DIPLOPIA = EXO

Bone of the skull

Frontal

Parietal

Temporal

Occipital

Maxillary

Zygomatic

Optic canal

Superior orbital fissure

Inferior orbital fissure

Bones of the Orbit: Memorize all seven…the ethmoid bone is very thin, and orbital cellulitis may be caused by infection migrating from the ethmoidal sinus to the orbit. Trauma may cause a “blowout” fracture (most commonly inferior, at the posterior medial part of the orbital floor in the maxillary bone). Orbital contents may prolapse through the fracture and become entrapped, and diplopia with limitation of upgaze, downgaze, or both may occur.

Muscles

Orbicularis oculi (controlled by CN VII)

Superior tarsal muscle (controlled by sympathetic system)

Levator (controlled by CN III) and levator aponeurosis

Dilator of the pupil (controlled by sympathetic system)

Constrictor of the pupil (controlled by parasympathetic system)

Ciliary muscle (controlled by parasympathetic system)

Google Drive Folder “Lid and External Feature Photos”

External

Eye brow

Superior orbital rim

Inferior orbital rim

Cilia (100 – 120 upper, 50- 75 lower)

Palpebral fissure

Lateral canthus

Medial canthus

Palpebral portion of the conjunctiva

Bulbar portion of the conjunctiva

Superior and inferior conjunctival fornix

Plica semilumaris (semilunar fold)

Caruncle

Eyelid margin

Tear Production / Internal Eyelids

Tarsal plates (inferior and superior)

Meibomian glands (30 – 40 upper, 20 – 30 lower)….produce the lipid portion of tears.

Meibomian gland orafices / pores

Main lacrimal gland (produces 95% of the aqueous portion of tears)

Accessory lacrimal glands (produce 5% of the aqueous portion of the tears)

Tear Drainage

Superior and inferior lacrimal punctum (lacrimal puncta)

Superior and inferior lacrimal canaliculus

Nasolacrimal sac

Nasolacrimal duct

Valve of Hasner

Google Drive Folder “Orbital Septum and Ligament Photos”

Tarsal plates (inferior and superior)

Orbital septum…attaches to the levator aponeurosis and tarsal plate superiorly, and the capsulopalpebral fascia and tarsal plate inferiorly

Orbital fat

Google Drive Folder “Cornea, Iris and Tear Photos”

Cornea

Central cornea

Paracentral cornea

Peripheral cornea

Limbal cornea / limbus

Corneal Layers from Outer to Inner

Corneal epithelium

Bowman’s layer

Corneal stroma

Descement’s membrane

Corneal endothelium

Pupil and Iris

Iris: Iris collarettes, iris crypts, iris root / iris insertion

Pupil, pupillary margin, pupillary ruff

Dilator muscle of the iris

Sphincter or constrictor muscle of the iris

Tear Layers

Lipid tear layer (made by the meibomian glands)

Aqueous tear layer (made by the main and accessory lacrimal glands)

Mucin layer (made by the conjunctival goblet cells of the cornea and conjunctiva)

A simple model of tears has three layers, from outer to inner; lipid, aqueous, and mucin.

The lipid portion of the tears controls tear evaporation, provides lubrication for smooth eyelid movement, creates a smooth optical surface at the tear-air interface, and helps the aqueous layer adhere (stick) to the eye.

The aqueous portion of the tears helps create a smooth optical surface, and contains proteins and many special substances (like lactoferrin and IgA) to protect the body and resist microbes. The aqueous portion of the tears also helps carry away dust and debris.

The mucin layer of tears is produced by conjunctival goblet cells and glycocalyx secreted by the surface epithelial cells. This layer helps the hydrophilic aqueous layer adhere (stick) to the hydrophobic corneal surface.

Google Drive Folder “Anterior Chamber Angle and Ciliary Body Photos”

Anterior segment

Anterior chamber

Anterior chamber angle

Schwalbe’s line

Trabecular meshwork

Schlemm’s canal / Canal of Schlemm

Scleral spur

Ciliary body

Iris insertion / iris root

Posterior chamber

Posterior segment

Trabecular meshwork

Schlemm’s canal / Canal of Schlemm

Ciliary body

Pars plana of the ciliary body

Pars plicata of the ciliary body

Ciliary processes (70 – 80)

Zonules / Zonular fibers

Ciliary muscle of the ciliary body : Longitudinal ciliary muscle and radial ciliary muscle

Google Drive Folder “Layers of the Eye”

Conjunctiva

Tenon’s Capsule

Sclera

Lamina cribosa of the sclera: The optic nerve contains approximately 770,000 – 1.7 million axons, which are gathered together into about 1,000 bundles called fascicles. These fascicles pass through sclera at the lamina cribosa and cribiform plate, then form the optic nerve.

Choroid

Retina

The uveal layer = (from anterior to posterior) iris +ciliary body + choroid

Gross Retinal Anatomy

LIGHT

Inner limiting membrane

Nerve fiber layer Retinal Nerve Fibers to the Lateral Geniculate Body + 6 other places

Ganglion cell layer

Inner plexiform layer Retinal Ganglion and Amacrine Cells

Inner nuclear layer

Outer plexiform layer Bipolar and Horizontal Cells

Outer nuclear layer Photoreceptors

Outer limiting membrane

Photoreceptor layer

Visual Processing

Retinal pigment epithelium

Applied Retinal Anatomy in the Clinic

Retinal Detachment

Separation of the neurosensory (inner) retinal layers from the retinal pigment epithelium (RPE)

Three Kinds of retinal detachment:

- Rhegmatogenous retinal detachment: A break in the retina allows vitreous fluid to enter the subretinal space (between the RPE and inner retinal layers)

- Traction retinal detachment: Proliferative (neovascular) membranes on the retinal surface or vitreous can pull on the neurosensory retina, causing a separation between it and the RPE

- Exudative or serous retinal detachment: Caused by an accumulation of subretinal fluid due to inflammation, exudative retinal diseases, or choroidal neoplasm

Retinoschisis

Splitting at the outer plexiform layer of the retina

Two Kinds of retinoschisis

- Typical senile retinoschisis with a shallow elevation of inner retinal layers

- Reticular retinoschisis, with bullous elevation

Retinoschisis is an immobile smooth, transparent elevation of the inner retinal wall, with no retinal tears, demarcation lines, or vitreous pigment cells like would be found in a retinal detachment. In retinoschisis the scotoma is absolute, whereas the scotoma in a retinal detachment is relative, and there is no demarcation line, like may be found in retinal detachment.

There may be outer wall breaks 10-27% of the time, and if schisis fluid accumulates in the subretinal space, an associated retinal detachment (schisis detachment) may occur.

Bruch’s Membrane

Bruch’s membrane is the innermost layer of the choroid, made of five layers. The innermost layer is the RPE basement membrane, and the outer layer is the choriocapillaris basement membrane.

RPE Detachment

An RPE detachment is a separation between the RPE and the innermost part of Bruch’s membrane. This space may be filled with blood, serous exudates, drusenoid material, or fibrovascular tissue.

Retinal Drusen

Retinal drusen are the most important sign seen during ophthalmoscopy that indicates a patient may have age-related macular degeneration (ARMD), which is an acquired retinal degeneration that may cause significant central vision loss. Drusen are located between Bruch’s membrane and the displaced-attenuated RPE located inner to the drusen.

Google Drive Folder “Retinal Regions and Landmarks”

Fovea

Macula

Retinal vascular arcades

Central retinal artery

Central retinal vein

Posterior pole

Equator

Ora Serrata

Google Drive Folder “Lens and Vitreous”

Lens capsule

Anterior subcapsular area and posterior subcapsular area

Lens cortex

Anterior and posterior Y sutures

Lens nucleus

Lens zonules

Vitreous humor

Nerve Supply to the Eye and Adnexa

Motor: CN III, CN IV, CN VI, CN VII

Sympathetic system to the superior tarsal muscle (raise upper eyelid)

Sympathetic system to the dilator muscle of the pupil

Sympathetic system to the blood vessels of the eye and lacrimal gland

Parasympathetic system to the constrictor muscle of the pupil

Parasympathetic system to the ciliary muscle to accommodate

Parasympathetic system to the blood vessels of the eye and lacrimal gland …more tears

Cilary ganglion: Located in the muscle cone between the lateral rectus and CN II, parasympathetic fibers synapse here and then travel to the eye with the short ciliary nerves (V1). Most fibers innervate (supply) the ciliary muscle, with only about 3% going to the iris sphincter.

Superior cervical ganglion: Sympathetic fibers synapse at the superior cervical ganglion before traveling to the eye.

Sensory CN V: V1, V2, V3

The Optic Nerve: The retinal nerve fiber layer contains between 770,000 and 1.7 million axons, which make a 90-degree turn at the optic disk to become the optic nerve. The portion of the optic nerve inside the eye can be divided into two sections; the prelaminar section and the laminar sections. “Laminar” refers to the lamina cribosa. The axons of the nerve fiber layer, which are unmyelinated, are bundled into about 1,000 fascicles which pass through the cribiform plate of the

lamina cribosa. They then become myelinated and continue on to form the optic chiasm, and optic tract on their way to the lateral geniculate body.

The optic nerve is 5-6 cm long, and can be divided into four sections: The intraocular section (0.7mm to 1mm long), the intraorbital section (30mm long), the intracanalicular section (6mm to 10mm long), and the intracranial section (10mm to 16mm long). The nerve is about 1.5mm in diameter at the level of the retina, but after being bundled into fascicles and myelinated is about 3mm in diameter.

Blood Supply to the Eye and Adnexa

Blood Supply to the Uveal Tract (Iris, Choroid, Ciliary Body)

Branches of the ophthalmic artery supply the iris, choroid, and ciliary body:

Short posterior ciliary arteries

Circle of Zinn formed by pial branches and branches of the short posterior ciliary arteries

Long posterior ciliary arteries

Muscular arteries

Anterior ciliary arteries

Major circle of the iris

Minor circle of the iris formed by arteries from the major circle of the iris traveling anteriorly

Blood Supply to the Retina

The outer retina is supplied by the RPE cells, which actively transport nutrients from the choroid layer to the retina and discharge waste from the retina to the choroid layer.

The posterior choriocapillaris is formed by branches of the short posterior ciliary arteries…the posterior choroid extends anteriorly to the equator of the eye

The anterior choriocapillaris is formed by branches of anterior ciliary arteries plus the two long posterior ciliary arteries

The inner retina is supplied by the central retinal artery and vein.

Vortex Veins: The vortex veins drain blood from the choroid. There is at least one retinal vein per quadrant of the retina

Blood Supply to the Extra-Ocular Muscles, Sclera and Conjunctiva

The extra-ocular muscles, sclera, and conjunctiva are supplied by branches of the ophthalmic artery. The ophthalmic artery is a branch of the internal carotid artery.

Venous Drainage of the Eye

The vortex veins of the eye drain to the cavernous sinus and the pterygoid plexus.

Lymphatic System of the Eye

The lymphatic system of the eye drains to the pre-auricular and parotid lymph nodes.

The Visual Pathway

Retina (nasal and temporal hemifields), optic nerve, optic chiasm, optic tract

Lateral geniculate body, optic radiations, visual cortex

Classic visual field defects associated with lesions to the retina, optic nerve, optic chiasm, optic tract, or visual cortex, including pituitary tumor

Ocular Anatomy Pertinent to Glaucoma

Aqueous generation by the ciliary body

Aqueous outflow through the trabecular (90%) and uveoscleral outflow (10%) pathways

Structures of the anterior chamber angle, narrow angle glaucoma…”CSTS”

The role of the iris in relative pupillary block

The role of the longitudinal cilary muscle attachment at the sclera spur in glaucoma treatment with pilocarpine

Glaucoma treatment with prostaglandin analogues to enhance uveoscleral outflow through the ciliary body

The role of lens zonules and the iris in pigmentary glaucoma

The “classic” appearance of a healthy optic nerve head, and the “classic” changes due to glaucoma…”ISNT”

“Classic” retinal nerve fiber changes associated with glaucoma…retinal nerve fiber layer defects

The lamina cribosa and the mechanical theory of glaucoma vs. the perfusion theory of glaucoma