Ophtho3- Retina

photoreceptors- rods and cones

• nerve fiber layer
• ganglion cells
• inner plexiform
• inner nuclear
• outer plexiform
• outer nuclear
• photoreceptors
• retinal pigment epithelium
• [in animals, light has to travel through all of these layers, giving them a lower quality acuity vision; humans have a fovea, an area of only photoreceptors, giving higher acuity vision]

• 1. Photons of light enter eye
• 2. Light passes through the transparent media to the sensory retina
• 3. Light passes through photoreceptors (rods and cones)
• 4. Some photons are absorbed and converted to an electrical potential
• 5. Remaining light passes through the retinal pigmented epithelium to the tapetum and is reflected back to the retina--> more photons converted to electrical potential
• 6. Electrical impulse transmitted to the bipolar neuron, where it is integrated and modified
• 7. Modified impulse then transmitted to the ganglion cell, which becomes the optic nerve
• 8. Optic nerve perforates the sclera at the lamina cribosa
• 9. The two optic nerves meet at the optic chiasm, > or = 50% nerve fibers decussate
• 10. Optic tracts continue to either the pretectum (received papillomotor fibers) or the lateral geniculate body (receives vision fibers)

• night vision
• motion
• [dogs, cats, and horses have mostly rods]

• day vision
• color (dogs, cats, and horses are di-chromads, only 2 types of cones; humans have 3)

retina; optic nerve; electrical impulse; fenestrated to allow the electrical impulses out (this is a weak spot in the eye; trauma can pop the optic nerve off the back of the eye)

posterior portion of the uvea; supplies nutrition to the rods and cones

highest blood flow per size of any organ in the body

• systemic infectious disease
• vascular disorders
• hypertension/ hyperviscosity
• CNS disease

• 1. Penlight exam- evaluate PLR and tapetal reflection
• 2. Dazzle reflex- subcortical response- requires intact retina and optic nerve and functional eyelid/ ability to turn head; bright light--> avoidance of painfully bright light
• 3. Cotton ball- throw cotton ball, does the eye track the cotton ball
• 4. Menace response- learned response (if you don't get one, touch the eye then try again)
• 5. Maze test- put obstacles on the floor and see if the dog runs into them
• 6. Fundic exam- DILATE PUPIL (only if animal does not have glaucoma), turn down lights

requires functional retina, CN II afferent, CN VII efferent

• indirect (best for small animal)
• direct
• panoptic

• examination of ocular fundus, especially in small animals
• hold ophthalmoscope at arms length from the animal's eye, get at eye level with the animal, shine upward to see the tapetal reflection, the image of the fundus is upside down and reversed

• examination of the ocular fundus, especially in large animals
• detailed examination of specific areas such as the optic nerve ad blood vessels with higher mag
• [not a good screening tool for small animals]

• upright image
• greater magnification than indirect
• smaller field of view than indirect

similar mag and field of view as indirect BUT includes a prism that flips the image to upright! great

• optic nerve: size, elevation/ depression
• retinal blood vessels: color, margins, hemorrhage, perivascular cuffing (inflammatory exudate and vasculitis around vessels), lipemia retinalis, hyperviscosity (thickened, spasming vessels)
• reflectivity: hyper- versus hypo-

• well-demarcated margins, localized: inactive, healed area of inflammation
• poorly demarcated margins: active disease
• generalized: PRA, glaucoma, SARDS, nutritional deficiency, severe inflammation

the retina is b/w you and the tapetum; therefore, retinal degeneration and atrophy lead to a brighter tapetum

fluid/ edema, fluid with protein, inflammatory cells, blood, neoplastic cells, retinal folds/ dysplasia, retinal detachment

• quantitative and qualitative assessment of photopic (cones) and scotopic (rods) retinal FUNCTION
• prior to cataract surgery
• sudden onset blindness, such as SARD's suspect
• evaluation for progressive retinal atrophy

night response; day response

any puppy or kitten <12-16 weeks old

Camelids, rats, primates, turtles, birds

• senile (>12-15 years old)
• inherited (progressive retinal atrophy)
• SARDS
• secondary [glaucoma, inflammation, detachment, trauma]

• inherited in specific breeds
• occurs at specific ages in each breed
• progress occurs in a known fashion

• tapetal hyperreflection
• pale optic disc
• vascular attenuation
• pupils may be dilated and PLR slow and incomplete
• night blindness (nyctalopia)
• progress to total blindness with time

acute blindness with a complete detachment (with partial detachments, the dog doesn't really show signs)

• hypertension
• inflammatory (immune-mediated, infectious)
• hyperviscosity
• hypermature cataract (inc. risk of vitreous degeneration and retinal detachment)
• congenital retinal dysplasia
• breed-associated acquired (bischon, shih tzu, etc)
• trauma

• systolic pressure > 180mmHg
• diastolic pressure > 95mmHg

• #1 renal disease
• #2 diabetes mellitus
• hyperthyroidism in cats
• pheochromocytoma
• idiopathic

vessel expanding and contracting to try a regulate flow/ pressure- sign of early hypertension

• "butt crack sign"- two leaves of retina flapping in the wind, veil of tissue behind the lens, hyporeflectivity
• fixed and dilated pupils
• absent menace
• absent PLR

• amlodipine
• enalapril

uveo-dermatologic syndrome (VKH) [akita, samoyed, sibes] by causing choroiditis

Blasto, Crypto, Histo, etc

diode laser retinopexy

• folds
• geographic
• complete

FeLV or FIV in the late third trimester or soon after queening

mild retinal dysplasia, which appear as single or multifocal retinal folds (areas of hyporeflectivity); areas that are thicker than normal

• larger (than folds) areas of retinal dysplasia
• most common right above the optic disc

• most severe form of retinal dysplasia in which the retina formed but was never attached
• results in blindness in that eye

PIFM--> glaucoma--> evisceration and prosthesis

• [sudden acquired retinal degeneration syndrome]
• 2-3 months after onset of clinical signs, generalized retinal degeneration

• acute onset blindness
• PLR variable (from fixed and dilated or sluggish to normal)
• no visible fundic abnormalities on initial presentation
• 2-3 months later, generalized retinal degeneration ("swiss cheese retina"- hyperreflective foci)
• history of PU/PD, polyphagia, and weight gain
• increased ALPCAP, cholesterol, or liver values [suggest cushings or hepatic disease- BUT negative when tested for cushings]

unknown

no treatment, dog will go blind

• retrobulbar optic neuritis (dilated and non-responsive pupil)
• cortical blindness (normal PLR)
• [important to differentiate b/c these diseases are treatable]

electroretinogram- normal ERG response indicates normal retinal function (points to treatable diseases)

• enrofloxacin (at therapeutic doses!)
• irreversible

• micropapilla/ optic nerve hypoplasia (congenital lack of formation)
• coloboma (congenital malformation)
• papilledema/ papillitis/ optic neuritis
• optic nerve atrophy/ degeneration

• micropapilla- smaller than normal optic nerve is a visual eye
• optic nerve hypoplasia- associated with blindness

when a nerve dies/ degenerates, it does NOT GET SMALLER- it gets sunken, darker, cupped, depressed

congenital pit or defect in the optic nerve and often adjacent sclera, notched iris, eyelid agenesis

most do not cause clinically significant changes in vision, but severe colobomas may result in visual disturbance and predispose to retinal detachment

optic nerve cupping secondary to chronic glaucoma (take IOP!)

non-inflammatory swelling of the optic nerve (associated with increased ICP or mass lesions compressing the optic nerve)

• papilledema usually doesn't affect vision
• papillitis is associated with a decrease in vision and decreased to absent PLR

inflammatory diseases of the optic nerve or adjacent choroid and retina, result of trauma, chronic glaucoma

• gray, flat optic nerve
• vascular attenuation
• cupping or depression of optic nerve (glaucoma)
• peripapillary hyperreflectivity