Posterior Segment Flashcards
describe vitreous anatomy
- elastic hydrogel
- 99% water, 1% collagen fibrils and hyaluronic acid
- very few cells (hyalocytes)
describe vitreous morphology
- 75% of volume of eye
- some role in refraction
- attachments formed by condensation of fibrils
-located at ora ciliaris retinae (peripheral retinal border) and pars plana ciliaris (posterior ciliary body), posterior lens capsule, around optic nerve - supports lens anteriorly, retina posteriorly
describe vitreous developmental abnormalities
- persistent hyaloid artery- failure of hyaloid artery to regress, usually small dense white or reddish string of tissue extending posteriorly from lens, may or may not have cataract
- persistent tunica vasculosa lentis
-fine, white strands extending from posterior lens capsule, remnants of embryonic blood supply - persistent hyperplastic tunica vasculosa lentis/persistent hyperplastic primary vitreous
-hereditary in dobermans, staffordshire terriers, sporadic in other breeds
-varies from small retrolentally located fibrovascular dots to malformation of lens and anterior vitreous
-posterior cataracts, fibrovascular plaque on posterior lens, lenticonus, vitreous, or intralenticular hemorrhage
describe vitreal degenerations
- syneresis: liquefaction of vitreous due to age or inflammation, may predispose to retinal detachment
- asteroid hyalosis: small white or pigmented particles consisting of calcium or phospholipids, move with eye movement
-usually incidental finding
-may be due to age or inflammation
-often appears sparkly or starry: small glistening particles in the vitreous body
-asteroid bodies: consist of calcium and phospholipids
-age-related changes with no impact on vision
list the layers of the fundus from outside to inside
- sclera
- choroid
- tapetum (+/-)
- RPE
- neurosensory retina
describe retinal morphology
- potential space between RPE and photoreceptors
- axons from ganglion cells form optic nerve; exit at optic disk
- area centralis: temporal to disk; area of higher cone density, devoid of blood vessels, usually blood vessels branching around it
- in most domestic animals, predominantly rod based (less color differentiation)
- light transmitted by electrical impulse to optic nerve, to optic chiasm, through optic tracts, to lateral geniculate body of thalamus then optic radiations to occipital cortex
describe the 10 layers of the retina? probs not any questions on it bc last year material
- RPE
- photoreceptor layer (rods and cones)
- external limiting membrane
- outer nuclear layer
- outer plexiform layer
- inner nuclear layer
- inner plexiform layer
- ganglion cell layer
- nerve fiber layer
- internal limiting membrane
how do we test the retina and optic nerve?
vision:
1. behavioral: owner history, maze testing in light and dark, cotton ball tracking
2. menace: retina, optic nerve, optic radiations, visual cortex, then CN VII for blink
retina/optic nerve functionality:
1. PLR: retina, optic nerve, parasympathetic anteromedian nucleus, then CN III to iris
- dazzle reflex: withdrawal response, subcortical
how do we directly test retinal function?
electroretinogram (ERG): light stimulation results in electrical response; measures photoreceptor activity
-usually prior to cataract surgery and in cases of blindness especially with normal ophthalmic exam
-NOT a good test of whether part of retina is detached; as long as some is attached, will still fire a wave form, so combine with ultrasound before cataract surgery too!
describe ultrasonography to assess the retina
useful when cannot visualize posterior segment
-can diagnose retinal detachment, vitreal abnormalities, tumors
describe ophthalmoscopy to examine the fundus
fundus is all structures of the posterior segment
usually split up into
1. tapetal fundus
2. non-tapetal fundus
3. optic nerve head (optic disk)
4. vasculature
best views from indirect! direct is super up close
describe indirect versus direct ophthalmoscopy to examine the fundus
indirect:
-larger field of view, lower magnification
-mag depends on size of lens used (higher diopter = less mag)
-good for examine entire fundus
direct:
-smaller field of view, higher mag, upright image
-usually used for closer exam of lesions, inspection of optic nerve
describe systematic evaluation of the fundus
- blood vessels:
-attenuated: abnormally small
-large
-tortuous: squiggly - tapetal reflectivity:
-increased or decreased - retinal hemorrhage
- detachments
describe the tapetal fundus
- variably triangular, located in superior fundus (tapetal = top)
- cats: yellow to green
dogs: green, yellow, orange, blue - color of fundus related to coat color
-color dilute animals, especially merles, may lack tapetum - small dogs = small tapetum
-large dogs = large tapetum
describe the non-tapetal fundus
- largest area of fundus
- junction between tapetal/nontapetal area highly variable, can be a distinct demarcation to a hazy transition area
- tan to dark brown
- reduced pigment (albinotic or subalbinotic animals) allows choroidal vasculature to be seen
-choroidal vessels larger, straighter, brighter orange than retinal vessels
describe retinal vessel patterns
- holangiotic retina:
-dogs, cats, ruminants
-extensive/visible retinal vascular supply
-usually 3-4 major venules, variable number of arterioles
-arterioles smaller and lighter in color - paurangiotic retina:
-horses
-small retinal vessels extending only a short distance from optic disc
-usually 30-60 fine vessels radiating from disc
describe normal variations of the optic nerve head
- dogs:
-located in tapetum or non-tapetum, quite variable myelination
-variation in myelination causes variation in nerve shape
-round, oval, triangular, polygonal
-pinkish white to deep pink - cats:
-located in tapetum
-not myelinated
-circular, greyish color
-conus: peripapillar hyperreflectivity
what are the 2 subdivisions of generalized progressive retinal atrophy?
most are autosomal recessive! (hared to breed out); untreatable and will ultimately result in blindness
- photoreceptor dysplasia: severe structural alterations of rods before retina completely developed
-rate of progression and loss of cones varies
-clinical signs in first year of life
-irish setters, norweigian elkhounds, collies, mini schnauzers, belgian shepherds
-alaskan malamutes: cone degeneration (day blindness), retain night vision throughout life - photoreceptor degenerations:
-degen after normal differentiation
-usually slower and later onset of disease
describe the clinical signs of progressive retinal atrophy (photoreceptor dysplasia or degeneration) (6)
- similar clinically across different breeds
- bilateral and leads to blindness
- decreased night vision usually first sign (rods affected first)
- progressive decrease in PLR, but may be present even when dog clinically blind
- eyes widely dilated at rest
- cataract formation in very late stages
describe the fundic exam findings of progressive retinal atrophy
early: subtle altered tapetal reflectivity, usually peripherally, and mild vascular attenuation
moderate:
-increase in tapetal reflectivity and vascular attenuation
-slight decrease in pigmentation of nontapetal fundus
-decreased myelination of optic nerve head
-optic nerve head atrophy
advanced:
-marked hyperreflectivity
-decreased pigmentation of nontapetal fundus
-marked vascular attenuaiton
-pale, demyelinated optic disc
describe sudden acquired retinal degeneration syndrome (SARDS)
- acute photoreceptor death
- usually middle aged dogs, females predisposed, all breeds affected
- clinical signs:
-often have weight gain
-polyuria, polydipsia, polyphagia for weeks to months prior to vision loss (Cushing’s like signs)
-acute vision loss- often over 24 hours
-dilated pupils
-minimal PLR
-normal fundic exam
describe diagnosis and treatment of SARDS
diagnosis:
1. electroretinogram to confirm loss of photoreceptor function
2. may have elevated ALP or other Cushing’s like changes on bloodwork but RARELY positive for Cushing’s
treatment:
1. none; permanent blindness
2. fundus will develop opthalmoscopically visible signs of degeneration over time, similar to PERA
describe retinal dysplasia
- histopath findings:
-linear folding of sensory retina with formation of rosettes
-abnormal formation of full thickness areas of retina - may have involvement of other structures of eye
- visual deficits depend on severity
-mild cases: no clinical sign - causes:
-hereditary (most common)
-herpes
-vitamin A deficiency
-radiation
-trauma, toxins - usually autosomal recessive if inheritance defined
-common in labradors, springer spaniels, terriers, beagles, cocker spaniels
describe clinical appearance of retinal dysplasia (4)
- focal or multifocal retinal folds or rosettes; appear as reduced tapetal reflectivity, grey or green dots or linear V or Y areas, usually superior to disk
- more severe form:
-geographic irregular or horseshoe shaped area usually in superior fundus
-usually hyperreflective with variable pigmentation
-may have focal retinal detachments
describe the vision thing with labradors/oculochondrodysplasia
- recessive effects on skeleton, incomplete dominant effects on eyes
- heterozygotes may be affected by multifocal retinal dysplasia only
- ocular: cataracts, complete retinal detachment
- skeletal: retarded growth of radius, ulna and tibia, hip dysplasia, hypoplasia of anconeal/coronoid processes
describe collie eye anomaly
- simple autosomal recessive, variable expression; do not breed affected animals!!
-collies, shetland sheep dogs, australian shepherds, border collies - abnormal mesodermal differentiation:
-defects in sclera, choroid, optic disk, retina, retinal vasculature - clinical findings:
-choroidal hypoplasia: pale to white area temporal or superiotemporal to disk; associated with abnormal, tortuous choroidal/retinal vessels
-usually no clinical signs
-posterior colobomas: usually involve optic disk or just adjacent to disk; grey or pink indentations of variable depths and variable clinical signs
–retinal detachment: often associated with colobomas; blindness
–intraocular hyphema: usually associated with retinal detachment and colobomas; blindness
how do you tell if a lesion is active? (3)
- fuzzy or indistinct borders
- hyporeflective tapetum (dull)
- raised areas
describe chorioretinal inflammations and infections
- usually primary choroidal, extends to retina - chorioretinitis
- retinochoroiditis: initially involved retina, spreads to choroid, uncommon
- clinical signs:
-may have no external signs
-if severe, may have red eye, signs of uveitis (panuveitis)
-vision loss if extensive
describe acute/active corioretinal inflammations and infections
- irregular margins of lesions
- often raised: extensive subretinal exudates may cause local or extensive retinal detachment
- edema: grey irregular borders
- retinal blood vessels: go over exudate, edema
- tapetal:
-indistinct, greyish/brownish areas
-white perivascular opacities (WBC accumulations/granulomas)
-hyporeflective areas (tapetum obscured/inflamed)
6.nontapetal: greyish to white areas; white perivascular opacities
describe chronic/inactive chorioretinal inflammations and infections
- distinct margins
- flat, not raised
- tapetal:
-hyperreflective areas (retina overlying tapetum is thinner)
-may have pigment clumping, blood vessel attenuation in area of lesion - nontapetal:
-depigmented areas with variable pigment clumping/proliferation
-blood vessel attenuation - optic nerve: pale, atrophied in some cases
describe differentials for chorioretinitis
Infectious:
viral: distemper, herpes, FeLV, FIV, FIP
bacterial: septicemia
rickettsial: ehrlichia
fungal: blasto, crypto, coccidiodes, aspergillus (esp chorioretinal exudates)
algal, protozoal, parasitic
Immune-mediated: IMTP (also retinal hemorrhage)
Metabolic: hypertension (also retinal hemorrhage and other badness, esp cats), hypoproteinemia
Neoplasia: lymphosarcoma, metastatic tumors
Idiopathic: usually only retinal detachments
describe diagnostics and treatment for chorioretinitis
diagnostics:
1. minimum database:
-CBC, chem, UA
-thoracic rads
-travel history
- titers by geography, blood pressure, fecal
- if extensive retinal detachment or vitreal inflammation, could do vitreal or subretinal tap
-fungal disease starts in choroid, organisms are located in the choroid or subretinal exudate, and anterior uveitis is secondary to posterior uveitis
treatment:
1. treat primary cause!
2. treat associated uveal inflammation (systemic anti-inflammatories)
describe retinal hemorrhages (5)
- appearance reflects anatomic location but doesn’t reflect underlying cause
- subretinal: dark, large
- intraretinal: punctuate
- superficial: flame shaped
- pre-retinal: globular, boat keel
describe retinal detachments (4)
- usually neuroretina separates from underlying retinal pigmented epithelium
-embryologic bases - small detachments: no visual defect
- large detachments: visual deficits or blindness
- two types:
-non-rhematogenous retinal detachments/exudative
-rhematogenous retinal detachments
describe non-rhematogenous retinal detachments/exudative/bullous (3)
- remain attached at ora ciliaris retinae (periphery) and at optic nerve
- bullous detachments, exudative retinal detachments (morning glory); due to inflammatory or exudative fluid displacing retina
- can also be due to vitreal traction bands secondary to vitreal inflammation or hemorrhage resulting in fibrous bands that contract and pull retina off RPE
describe opthalmoscopic appearance of exudative/bullous/non-rhematogenous retinal detachments
1.exudative/bullous detachments:
-anterior displacement of retina
-focal: may be an area of retina out of focus
- complete bullous attachment:
-retinal vessels may approach back of lens capsule
-often can see with transilluminator (penlight diagnosis)
describe differentials for retinal detachments
- exudative retinal detachments (WBC): same as chorioretinal inflammation
- bulbous (fluid): often associated with systemic diseases
-hypertension
-hypoproteinemia
-hyperviscosity
-polycythemia
-uveodermatologic syndrome
-idiopathic
describe diagnostics and treatment of non-rhematogenous retinal detachments
- ALWAYS systemic workup
-CBC, chem, UA, chest rads titers if any suspicion of infectious cause - treatment: underlying cause
-vision may or may not return with treatment of primary cause
-IF rule out systemic disease, may try oral steroids
describe rhematogenous retinal detachments (RRD)
- retinal tear or break present which allows vitreous to enter subretinal space
- dialysis: refers to separation of peripheral retina from attachments, also called disinsertional
-ophthalmic appearance: retina hangs on in grayish folds, obscuring optic nerve; tapetum is hyperreflective with no visible vessels - caused by:
-congenital abnormalities: collie eye anomaly; optic nerve colobomas allow vitreous into subretinal space
-shih tzus/lhasas: may have a primary vitreous abnormality that predisposes to RRD
-may be secondary to inflammation or trauma
-post cataract surgery potentially
describe surgical repair of retinal detachments
difficult! for rhematogenous or traction bands only (focal, non-inflammatory)
- simplest: laser retinopexy: rows of burns around detachment to create adhesions to prevent further detachment
- more complicated involves entering vitreous chamber, removing vitreous, and replacing with various oils or gases along with retinopexy
describe hypertensive retinopathy
- usually older cats, acute vision loss
- clinical signs due to precapillary vasoconstriction of retinal arterioles (autoreg) causing smooth muscle necrosis, vascular dilation, and leakage
-may occur in choroid as well, leading to retinal detachments
clinical signs:
1. hyphema
2. intravitreal hemorrhage
3. retinal vessel tortuosity
4. retinal hemorrhages
5. varying degrees of retinal detachment (sudden blindness)
- high blood pressure associated with cardiac, renal abnormalities, hyperthyroidism
diagnostics: blood pressure measurement, systemic workup
treatment: treat primary disease and lower BP
-quick retinal reattachment may result in regaining vision but retina may slowly degenerate over time
what causes retinal detachment in cats? (5)
- hypertension
- hyperviscosity syndromes
- infectious: toxo, crypto, blasto, histo, FIP
- neoplasia
- nutritional: taurine deficiency can cause central retinal degeneration
describe nutritional retinal degeneration in cats
stages:
1. increased granularity to area centralis
2. ellipsoid hyperreflective lesion
3. development of second hyperreflective lesion nasal to disk
4. two lesions coalesce to form horizontal band over disk
5. end stage: generalized retinal degeneration
-measure taurine levels and cardiac function
-no treatment to reverse retinal damage already done
-supplementation will prevent progression
describe chorioretinal development diseases in cats
retinal dysplasia: associated with FeLV or panleukopenia along with impaired development of cerebral and cerebellar tissues
describe chorioretinal inflammation in cats (2)
- ophthalmic signs similar to dogs
- due to:
- viral: FeLV, FIP, FIV
- bacterial
- fungal: cryptococcosis, histoplasmosis, blastomycosis
- parasitic
describe the optic nerve (4)
- an extension of rhe brain
- axonal projections of the retinal ganglion cells
- coalesce at optic nerve head (where myelinated)
- pass through lamina cribrosa of sclera to retrobulbar space
describe divisions of the optic nerve (4)
- intraocular: retinal ganglion cell layer, nerve fiber layer, optic nerve head, intralaminar (scleral region)
- intraorbital: posterior to globe
- intracanalicular: nerve within the canal
- intracranial: nerve from canal to optic chiasm
describe micropapilla/optic nerve hypoplasia/optic nerve aplasia (3)
- decreased number of retinal ganglion cells, unilateral or bilateral; visual deficit depends on severity; PLR variably affected
- appears round, small, and gray
-round due to lack of myelin - normal retinal vessels
describe otpic nerve colobomas (3)
- coloboma: defect or absence of ocular structure
- optic nerve coloboma: pits on or within nerve
-part or all of disk may be involved - found in collie eye anomaly, may predispose to retinal detachment
describe optic nerve inflammation (6)
- optic neuritis; uni or bilateral
- can involve any segment of optic nerve
- associated with sudden blindness, fixed and dilated pupils
- intraocular involvement:
-disk appears swollen, elevated, and hyperemic
-margins become indistinct - retrobulbar involvement: optic disk will appear normal
- ERG normal
describe ddx for optic nerve inflammation (5)
- infectious: distemper, blasto, crypto, histo, toxo
- trauma, toxins
- vitamin A deficiency
- neoplasia: reticulosis/GME
- idiopathic
describe diagnostics of optic nerve inflammation
- min database, chest rads, titers
- MRI or CT
- CSF tap
optic neuritis is a neuro disease!!
describe treatment of optic neuritis (3)
- treat primary cause
- systemic steroids: esp if cannot determine primary cause and have rule out infectious disease
- often poor prognosis for vision
describe optic nerve cupping (3)
1, secondary to long term elevated IOP
2. appears dark, depressed, round
3. poor prognosis for vision
describe optic nerve atrophy (2)
- pale nerve, myelin loss (becomes round)
- associated with PRA, chronic glaucoma, optic neuritis
describe traumatic optic neuropathy
- traumatic proptosis: optic nerve shearing due to laceration, or avulsion
-immediate vision loss with PLR deficit - may have damage further away from globe or ischemic damage
-if optic nerve intact, steroids may help
how would you approach a blind dog?
- menace, palpebral, PLR
- if you assess is blind, esp bilateral:
-see if light can get to back of eye: cornea, aqueous, lens clear enough for this: assess via tapetal reflection
-a dilated or constricted dog with a tapetal reflection SHOULD have vision
-if blind but still get tapetal reflection: issue in retina, topic nerve, or brain
-now look at retina: if grossly abnormal = detachment, inflammation, or progressive atrophy
-if retina looks normal: SARDS or optic neuritis
-if do ERG and retina doesn’t function, the issue is with optic nerve
