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Trevor Arnold, MS, DVM, DACVO. Animal Eye Center Ophthalmology specialty Hospital Two Board Certified Veterinary Ophthalmologists 2-3 Technicians 2 Front.

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Presentation on theme: "Trevor Arnold, MS, DVM, DACVO. Animal Eye Center Ophthalmology specialty Hospital Two Board Certified Veterinary Ophthalmologists 2-3 Technicians 2 Front."— Presentation transcript:

1 Trevor Arnold, MS, DVM, DACVO

2 Animal Eye Center Ophthalmology specialty Hospital Two Board Certified Veterinary Ophthalmologists 2-3 Technicians 2 Front Office staff cases a year

3 What is Veterinary Ophthalmology We provide a comprehensive list of services to all species (other than human of course) Adnexal disease and surgery Corneal disease and surgery Cataract management Glaucoma Uveitis Neurology Oncology Genetic /Inherited disease screening Research services Must also be able to diagnose and manage ocular manifestations of systemic disease Eg: Diabetes, Hyperthyroid, Infectious diseases etc

4 The Basics Understanding anatomy and embryology is essential for the effective practice of ophthalmology There are some fundamental anatomical differences between animals and humans Both on the gross anatomical and the cell level These differences do alter how we practice medicine, however, for the most part the general principals of ophthalmology are the same

5 “Primitive” Vision “Vision” most likely started as photoreceptive proteins (the original opsins) in single celled organisms which allowed these cells to move towards or away from light In multicellular organisms these proteins concentrated in cells (the original photoreceptors) Light sensing cells then aggregated to provide a primitive eye Evolutions Witness: How Eyes Evolved Ivan R. Schwab, Richard R. Dubielzig, Charles Schobert

6 “Primitive” Vision A flat surface cannot determine the direction of light very well and so the “visual” surface became curved Some organisms curve the light sensitive cells outward (eg. Compound eye) Others curve it inward (Humans, dogs, cats etc)

7 “Primitive” Vision Compound eye is made up of multiple Ommatidium Cornea Photoreceptors Nerve Pigmented cells

8 “Primitive” Vision Nautilus (Cephalopod) Developed an inwardly curved retina Forms as an invagination of the body as apposed to an outpouching of the brain Works like a pinhole camera Maximizes focus without the need for a cornea or lens

9 “Primitive” Vision Mantis Shrimp: Proof that you don’t need a complex eye to have complex vision Have at least 16 photopigments to help see color Can polarize multiple wavelengths of light Each eye moves independently and can provide depth perception individually

10 Embryology The embryologic development of the human and dog eye is generally guided by the same genes, proteins and tissue induction The canine eye is slightly less developed at birth compared to a human. It takes 2 weeks for the eyelids to open, however it typically takes 4-6 months for the eye to finish developing Recent advancements in gene therapy for Leber congenital amaurosis were discovered through work on a similar condition in dogs

11 Orbit Open orbit Dogs, cats etc The lateral orbit is composed of a ligament between the zygomatic and frontal bones The floor of the orbit is primarily the Pteragoid muscle Closed orbit Primates (Human) Horses, Cows, Birds, Fish

12 Muscles Most species have some form of: Dorsal, Ventral, Lateral and Medial rectus and the Dorsal and Ventral Oblique Dogs and Cats also have a retractor bulbi muscle (CNVI) Larger species regularly require an Auriculopalpebral nerve block to paralyze the levator palpebral superiorus in order to examine the eye

13 Adnexal Structures Eyelids (Entropion, Distichia, Meibomian tumors) Third eyelid(Semilunar fold in Humans) Dog s have two Lacrimal Glands Immune mediated dry eye is a common problem in dogs Cyclosporine’s effect on tear production was incidentally discovered by a veterinary ophthalmologist

14 Globe Birds, have bone, reptiles and fish have cartilaginous plates in their sclera The dog globe is roughly spherical Average 21 mm in diameter The size of the eye is remarkably similar in all breeds

15 Cornea Average corneal diameter in dogs 18mm Curvature 40D (Larger breeds have flatter corneas) Due to the size of the cornea very little sclera is exposed beyond the eyelids Makes scleral incisions for cataract surgery difficult The eye must be proptosed for vitreal surgery

16 Interesting Corneal Anatomy Some fish species have two corneal layers A scleral cornea and a dermal cornea Snakes have a scale that covers their eye (spectacle) This is normally shed when the skin is shed Big horn sheep and Manatees are two species with non-pathologic corneal vascularization

17 Corneal Pathology

18 Corneal Refraction The curvature of the cornea bends light into the eye Provides the most refractive power of the eye in terrestrial animals Tear film actually bends the light

19 Corneal Refraction What if you don’t live in air…or you live in both air and water? Most fish have very round lenses and depend less on their cornea Sea lions have a portion of their cornea that is flat They look through this part of the cornea when in air Some species constrict their pupil to a pinpoint to minimize the refraction that needs to occur to focus light on the retina

20 Iris and Pupillary Light Reflexes In cats there are bundles of iris sphincter muscles on either side of the pupil to control constriction One branch of CNIII controls the medial aspect and another controls the lateral aspect of the iris Birds have skeletal muscle in their pupil so they can actively control their pupil Can be difficult to dilate (risk of systemic paralyzation)

21 Pupils around the World

22 Methods of Accommodation Dog and Human Ciliary body muscles contract, this releases tension on the lens, allowing it to round up (I.e increases the curvature of the lens) Dogs only have an accommodation range of 3-4D (Human 15-16) Bird When ciliary muscles contract they push on the lens causing it to round up Some birds can also change the curvature of the cornea Some diving birds have an accommodation range of diopters Fish Have a special muscle (Retractor lentis) which moves the lens forward or backward to change focus Several fish can also change the corneal curvature Cats Combination of dog and fish accommodation techniques.

23 Cataracts The canine lens is considerably larger than the human 7mm thick (Up to 9mm with diabetic cataracts) Artificial PMMA or Acrylic lenses 11, 12, 13mm or 14mm 41D lens Dogs develop considerable inflammation

24 Glaucoma in Dogs Dogs typically present with an inherited Closed Angle Glaucoma It is extremely rare for dogs to present for vision loss prior to the onset of elevated intraocular pressures Common for dogs to have pressures of 50 mmHg or more at the initial presentation We can rarely save the first eye

25 Medical Management Dogs respond well to Prostaglandin Analogues Typically Latanoprost 0.005% Causes profound miosis in all dogs due to prostaglandin receptors in the smooth muscle Dorzolamide 2% Timolol does not tend to be as effective in dogs as it is in humans

26 Surgical Management Trans-scleral or Endolaser Cyclophotocoagulation Shunt placement Ahmed valved shunts are used most often Often fail due to fibrin occlusion or Bleb capsule thickening Trabeculectomy, Iridotomy and Iridectomy surgeries do not work in dogs A likely reason for low surgical success rates is the delay in intervention

27 Glaucoma In Cats Most often Secondary to chronic lymphoplasmacytic uveitis Middle to older age cats occasionally develop glaucoma secondary to Aqueous Misdirection Leads to over hydration of the vitreous, anterior displacement of the lens and collapse of the anterior chamber Interestingly Cats do not have PGF2A receptors inside the eye, and so Prostaglandin analogues do not help to decrease IOP

28 Retina Retinas are classified based on the vascular pattern Holangiotic, Merangiotic, Paurangiotic, Anangiotic Most primates and some birds, fish and reptiles have a Fovea Some species have more than one to help focus on two things at once Animals do have a location of the retina with a high density of cones (Area Centralis) Typically a horizontal band dorsolateral to the ONH

29 Retina Animals do have color vision Humans have three types of color photoreceptors Blue, Green and Red Dogs have two Blue and Yellow-Green (Similar to Red-Green color blindness) Some birds have 3-4 types of rods Fish have colored oil droplets that sit around the photoreceptors and to help maximize color perception

30 Tapetum Reflective layer of the choroid. Located below the RPE and above the choroidal vessels (In most species) Dogs and cats have a Cellular tapetum Horses and Ruminants (cows, sheep etc) have a fibrous tapetum

31 Holangiotic Dog, Cat, Primate, Ruminants

32 Merangiotic Rabbits

33 Paurangiotic Equine, Elephant

34 Anangiotic Birds, Reptiles Some mammals

35 Questions

36 Photo Credits wanderlustlizard.wordpress.com dc378.4shared.com tnrtb.wordpress.com


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