Sara Thomasy DVM, PhD, DACVO

Prosencephalon

Eye Fields

https://syllabus.med.unc.edu/courseware/embryo_images/unit-eye/eye_htms/eyetoc.htm

Mouse Day 7

Dog Day 10

Mouse Day 8

Dog Day 11

Cyclopia

Mouse Day 8

Dog Day 12

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

Mouse Day 9.5 Optic stalk

Optic

vesicle

https://syllabus.med.unc.edu/courseware/embryo_images/unit-eye/eye_htms/eyetoc.htm

Day 15

Mouse Day 9.5

Dog Day 15

Optic stalk

Optic

vesicle

Microphthalmia

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 Cataract Retinal dysplasia Colobomatous malformations

Merle ocular dysgenesis

Neural plate deficiency

Mouse Day 11

Dog Day 18

https://syllabus.med.unc.edu/courseware/embryo_images/unit-eye/eye_htms/eyetoc.htm

Intraretinal space

Iris coloboma

https://syllabus.med.unc.edu/courseware/embryo_images/unit-eye/eye_htms/eyetoc.htm

Mouse Day 11

Dog Day 18

“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

Mouse Day 11 https://syllabus.med.unc.edu/courseware/embryo_images/unit-eye/eye_htms/eyetoc.htm

Day 25

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)

A

B

C D

Pupillary membrane

Provides nourishment 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

Mouse Day 11.5

Hyaloid

artery

Lens

vesicle

Day 25

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

Mouse Day 13

https://syllabus.med.unc.edu/courseware/embryo_images/unit-eye/eye_htms/eyetoc.htm

Day 29

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

Rat

Gelatt et al. JAVMA. 1983;183:99-102.

Shastry BS & Reddy VN. Biochem & Biophys Res Commun. 1994 ;203: 1663-7.

Zhang et al. IOVS. 1991;32: 2662-5.

Gelatt et al. AJVR. 1983;44:1130-2.

Microphakia Immature Cataract

Microphakia HypermatureCataract Elongated CB processes

Small optic vesicle → small lens vesicle Concurrent microphthalmia

Abnormal optic vesicle orientation → small lens vesicle ± Cataract ↑ risk of lens luxation

Dog

Multifocal retinal dysplasia

“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

Dog

Optic nerve hypoplasia

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.

Mouse Day 17

Day 32

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