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I. Eye Development

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I. Eye Development Sara Thomasy DVM, PhD, DACVO Mouse Day 8 Dog Day 11 Eye Fields Mouse Day 7 Dog Day 10 Prosencephalon https://syllabus.med.unc.edu/courseware/embryo_images/unit-eye/eye_htms/eyetoc.htm Mouse Day 8 Dog Day 12 Cyclopia Cyclopia - Formation of a single median globe Synophthalmia – Two incompletely separated or fused globes Concurrent severe craniofacial defects Veratrum californicum . Day 14 of gestation in sheep Steroidal alkaloids . Cyclopamine and jervine . Inhibit sonic hedgehog signal transduction during gastrulation Affects midline neural plate Corn Lily or False Hellebore Day 15 Optic vesicle Mouse Day 9.5 Optic stalk https://syllabus.med.unc.edu/courseware/embryo_images/unit-eye/eye_htms/eyetoc.htm Mouse Day 9.5 Dog Day 15 Optic vesicle Microphthalmia Optic stalk https://syllabus.med.unc.edu/courseware/embryo_images/unit-eye/eye_htms/eyetoc.htm Optic vesicle deficiency Corresponding small palpebral fissure Failure of normal optic cup growth . Failure of fusion of the choroid fissure → colobomas . Failure to establish normal IOP Associated with a myriad of ocular defects ASD PHPV Neural plate deficiency Cataract Retinal dysplasia Colobomatous malformations Merle ocular dysgenesis Intraretinal space Mouse Day 11 Dog Day 18 https://syllabus.med.unc.edu/courseware/embryo_images/unit-eye/eye_htms/eyetoc.htm Mouse Day 11 Iris coloboma Dog Day 18 https://syllabus.med.unc.edu/courseware/embryo_images/unit-eye/eye_htms/eyetoc.htm “Defect” Failure of fusion of the choroid fissure “Typical colobomas” at the 6 o’clock position Abnormal differentiation of the outer optic cup “Atypical colobomas” at other locations Charlois Collie Collie Day 25 Mouse Day 11 https://syllabus.med.unc.edu/courseware/embryo_images/unit-eye/eye_htms/eyetoc.htm Persistent keratolenticular attachment Classic example: Peter’s anomaly Corneal opacity with stromal & DM defects (B) Persistent pupillary membrane (A) . Iris hypoplasia (C) . Anterior polar cataract (D) B A D C Pupillary Provides nourishment membrane to the developing lens Failure of the pupillary membrane to regress Strands arise from iris collarette DDx: Synechiae arise from pupillary margin Classified by location: Iris-to-cornea . Iris-to-iris . Iris-to-lens Predisposed breeds: Basenji Mastiff Pembroke Welsh Corgi Chow Chow Week 8 Postnatal ↑ IOP in animals <6 months of age . Marked buphthalmos → scleral elasticity Arrest in normal development of AC . Concurrent ocular anomalies (eg. ASD) ↑ IOP in animals <6 months of age . Marked buphthalmos → scleral elasticity Arrest in normal development of AC . Concurrent ocular anomalies (eg. ASD) Failure of the PL to rarify during development “Primary” glaucoma . Many predisposed breeds http://www.eyedvm.com/eyeinfo.html Day 25 Hyaloid artery Lens Mouse Day 11.5 vesicle Failure of the hyaloid artery to regress Rat Concurrent cataract Challenging surgery! Ultrasound all surgical candidates Failure of vascular regression Normal vitreous - antiangiogenic Concurrent anomalies Microphthalmia Microphakia Cataract Retinal dysplasia Inherited trait Doberman Staffordshire Bull Terrier Rat Day 29 Mouse Day 13 https://syllabus.med.unc.edu/courseware/embryo_images/unit-eye/eye_htms/eyetoc.htm Abnormal formation of 1º 0r 2º lens fibers Nuclear Nonprogressive Abnormal lens vesicle invagination, separation or defects in lens epithelium/capsule Peripheral Rat Miniature Schnauzer Autosomal recessive Bilateral Posterior cortex → rapid progression Microphthalmia Shastry BS & Reddy VN. Biochem & Biophys Res Commun. 1994 ;203: 1663-7. Zhang et al. IOVS. 1991;32: 2662-5. Gelatt et al. JAVMA. 1983;183:99-102. Gelatt et al. AJVR. 1983;44:1130-2. Rat Microphakia Immature Cataract Microphakia Hypermature Cataract Elongated CB processes Small optic vesicle → small lens vesicle Concurrent microphthalmia Abnormal optic vesicle orientation → small lens vesicle ± Cataract ↑ risk of lens luxation Multifocal retinal dysplasia Dog “Difficult formation” Incomplete contact between inner & outer optic cup Classified by severity: Focal/multifocal → retinal folds → inequity in growth of inner and outer optic cup Dog Dog “Difficult formation” Incomplete contact between inner & outer optic cup Classified by severity: Focal/multifocal → retinal folds → inequity in growth of inner and outer optic cup Geographic Diffuse with retinal detachment Dog Dog Optic nerve hypoplasia Dog RGC axon guidance defect Abnormal retinal/ON development ↓/Absent vision (2/8 cases visual) Histologic features: Vestigial ectopic ON elements (no axons) – 6/8 cases Vitreous extension of retinal vessels – 5/8 cases Predisposed breeds: . Poodle . Shih Tzu da Silva EG, et al. Vet Ophthalmol. 2008 ;11:23-29. Primary failure of RGC development Failure of RGC axon initiation &/or guidance Failure of RGC axons to reach optic disc Concurrent ASD (3/5 cases) Lack of: Retinal vessels NFL RGCs da Silva EG, et al. Vet Ophthalmol. 2008 ;11:23-29. Day 32 Mouse Day 17 Abnormal differentiation of an isolated group of cells (early) Abnormal invagination of ectodermal tissue (late) Common locations (surface ectoderm derived): Cornea (at the lateral limbus) Eyelid Conjunctiva Choristoma – Normal tissue in an abnormal location Corneal dermoid Hamartoma – Tissue normal to that location but in an abnormal configuration Eyelid dermoid Predisposed breeds: Dachshund Dalmation Doberman German Shepherd St. Bernard Eyelid Agenesis Abnormal orientation of the optic vesicle as it contacts surface ectoderm Temporal aspect of superior eyelid Common sequelae: Exposure keratitis Common concurrent abnormalities: Anterior segment dysgenesis Coloboma Choroid Optic nerve Photo courtesy of Dr. Daniel Dorbandt, University of Illinois Roberts & Bistner procedure . Dziezyc & Millichamp modification Z-plasty Cutler-Beard technique Mustarde cross lid technique Sliding skin grafts Cryotherapy Collagen injection Lip to lid transposition .
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