Veterinary Ophthalmology Exam Notes - Retinal Structure and Function in Dogs and Other Animals

Retinal Pigment Epithelium (RPE)
- Key component of the retina; responsible for absorption of light and support of photoreceptors.
- Types of pigmentation observed in dogs:
- Dogs may have no pigment (no retinal pigment) leading to visibility of the choroid.
Tapetum Lucidum
- Reflective layer in the eyes of many animals including dogs, which aids night vision.
- Appearance can vary between smaller and larger dogs, with smaller dogs often having a smaller tapetum.
- Absence of tapetum results in visibility of choroidal lenticels.
Choroidal Vasculature
- Superficial choroidal tapetum and pigmentation in RPE may block view of the choroid in normal dogs.
- In cases with no or little RPE pigment, the choroidal vasculature is more visible.

Orbital Blood Vessels
- Differentiating normal orbital blood vessels from abnormal findings (e.g., redness) is important for diagnosis.
Diagrams and References
- Diagrams referenced from G6 and Millichick color atlas can aid in understanding and visual identification of retinal structure.
Optic Nerve and Blood Vessels
- Migration of blood vessels onto the optic nerve is a common observation in different retinal structures.
- The relationship between the tapetum and blood at the periphery.

Cats
- Cat optic discs are similar in structure but lack myelin, giving them a gray appearance in the optic nerve.
- Like dogs, cats may or may not possess tapetum and pigment in non-tapetum areas.
Horses
- Optic nerves tend to have pink coloration, with visible arteries and veins radiating outwards.
Cattle
- Optic nerves often translucent with large superficial blood vessels.
Rats
- Unique optic discs with a central depression and myelinated blood vessels.
Birds and Reptiles
- Birds often have no retinal blood vessels, relying on choroidal vasculature.
- Reptiles may have unique structures like the pecten and conus papillaris providing nutrient functions.