Flashcards in Problem solve - abnormal eye Deck (45):
Where can SOLs arise from in the orbit?
- extraocular mm
- BVs, nn and CT
- glands: lacrimal, TE, zygomatic salivary
What can cause a SOL? 3
- Infection/ inflammation (abscess/ cellulitis)
- Neoplasia (usually malignant)
- Specific tissue inflammation (i.e. extraocular polymyositis)
CS - orbit SOL
1. Globe displacement (frequently dorsolateral but depends on mass location, frequent anterior component - exopthalmus
2. protrusion of the TE
3. change in facial symmetry - TE, globe position
Describe appearance of microphthalmia
= small eye from birth
- usually bilateral
- may also have ocular defects (e.g. cataracts)
- rarerly too dticking
Cause - micropthalmia
*Destruction of CS (cyclodestruction):
- sequela to inflammation, Pthisis bulbi (severe uveitis)
- targeted surgical destruction (excessive laser cycloablation)
-chemical ablation (injection of gentamycin into vitreal cavity)
- increased size of the globe itself
- due to increased IOP - glaucoma (primary or secondary)
- high IOP leads to stretching and other changes:
- conjunctival and episcleral BV congestion
- corneal oedema (due to endothelial damage)
- Haab's striae ('stretch marks', breaks in Descemet's membrane)
- Zonular tears
- Corneal ulcer (due to mild/moderate corneal overexposure)
What are zonular tears? What is the classic sign?
- overstretching of fibres (lens displacement)
- usually in one area initially
- lens equator edge is visible through pupil (aphakic crescent)
What does increased IOP with glaucoma cause?
damage to optic nerve head and neural retina
Describe normal retina
- 10 layers; 1 epithelial (RPE), 9 neural (ganglia, rod, cone)
- Ganglion cell axons collectively make the optic nerve
2 forms of glaucoma
primary and secondary
abnormal iridocorneal angle (ICA) due to malformation
2 forms of primary glaucoma
- Closed angled = most common in dogs, rapid onset, dramatic, 1 eye first, within 6 months the second eye will be affected
- Open angle = most common in people, insidious onset, also beagles and elkhounds
ophthalmic examination of the AC
What is the pathological process of secondary glaucoma?
Something is affecting the ICA (outflow):
- blood, fibrin, PFIMs (when they encolse the ICA), WBCs, neoplasia (primary or metastatic)
- inflammation (uveitis) - various causes: cataracts, infectious uveitis (FIP, leishmania)
- hyphema (various causes)
- lens luxation
- intraocular/ metastatic neplasia
Species affected by secondary glaucoma
dogs and horses, also cats
Outline feline glaucomas
- Primary forms exist (Burmese)
- Often secondary and mostly associated with uveitis (FIV, FeLV, FIP, Toxoplasma as --> keratic precipitates. Also idiopathic)
What is the long/short term perspective of glaucoma?
- possible only one eye is affected if secondary
- you might lose the affected eye or tx it and it might not recur
- secondary glaucoma might be less worrying if you are lucky
- primary affects both eyes over time, always
- overall, long-term monitoring /tx of second eye is needed
- no breeding problem with secondary glaucoma, except lens luxation
- primary glaucoma worrying for breeding if onherited.
Cause - lens displacment
overstretching of zonules and tears
Define aphakic crescent
- a crescent shaped gap
- tear of zonules and lens movement away
- development of crescent between pupil and lens
CS - moderate IOP and higher (glaucoma)
- mid-dilated non-responsive pupil
- conjunctival and episcleral BV congestion
- +/- vision problems (negative menace/ vision maze test)
- increased IOP
CS - high to very high IOP (glaucoma)
- corneal oedema (blue, rare in cats)
- Haab's striae
- cupping of optic nerve head (maximal pressure damage at edge of optic nn head, soft myelin/ fibres are 'punched in')
- lens displacement
- corneal ulceration also possible
Tx principles - glaucoma
- control IOP
- if secondary, remove cause if possible (tx inflammation, remove lens from AC surgically, remove eye with problem tumours)
How can IOP be controlled?
ANTI-HYPERTENSIVE DROPS (several types)
- carbonic anhydrase inhibitors
- prostaglandin analogue
Outline beta blockers as an anti-hypertensive for glaucoma tx,
- e.g. timolol
- reduce production of aqueous part
- weak cardiac and respiratory effects in smallies
Outline carbonic anhydrase inhibitors as an anti-hypertensive for glaucoma tx
- e.g. dorzolamide
- reduce production of aqueous part
- block CA enzyme in CB epithelium
- BID to TID
- works well in combination with beta-blocker
- good in cats and horses
Outline prostaglandin analogues as an anti-hypertensive for glaucoma tx
- increases humor outflow
- SID (evenings) or BID
- note the nearly ridiculously-low concentration
- strongest, but can cause inflammation as it is an inflammatory mediator
- DOESN'T work in cats, works in horses
What are IOPCs?
= intraocular pressure curves
- require hospitalisation
- it is the serial measurement of IOP q3 hours for about 30 hours.
- don't use proxymetacaine as local anaesthetic for IOPCs as epitheliotoxic
Distinguish phacodonesis and iridodonesis. Which dog breeds?
- Phacodonesis is subtle lens trembling movement when the globe moves, only visible if cataractous. Iridodonesis is subtle iris trembling movement when the globe moves.
Both often occur together at the early stages of primary lens luxation: subluxation.
- inherited in TERRIERS (also collies)
What is anterior presentation of the vitreous?
= strand floating in AC, mucus-like, means AH can't pass from PC to AC.
What is posterior luxation (subluxation and luxation)?
DEEP AC: iris rests on the lens and it bows forward as a result. If the lens falls backward, the AC deepens.
Sequelae - posterior lens luxation
- lens-induced uveitis
- lens adhesion to retina
Is anterior or posterior luxation usually more severe?
anterior luxation usually more severe
Sequelae - anterior luxation
Pupil becomes blocked (v. rapid, mins-hours)
Outline AH dynamics
formed by CB, moves anteriorly, exits mainly via ICA.
Sequeala to anterior lens luxation
- pupil block glaucoma (entire lens is visible, iris is behind the lens)
- damage to corneal endothelium (central cornea)
CS - subluxation/luxation
- deep AC
- anterior presentation of vitreous
- anterior or posterior luxation
- increased IOP (variable in subluxation, acute and large increase with anterior luxation = emergency)
Lens luxation - aetiology
- other breeds
- genetic mutation ID, test developed by AHT
- spontaneous in other breeds that don't have the (so far) only known genetic mutation.
What happens in pupil block glaucoma and other ?
(pupil block glaucoma= a sequel to anterior lens luxation)
- with rapid and high increase in IOP, damage to:
- retinal ganglion cells (axons form optic nn)
- optic nn head (axoplasmic flow stops)
- (BVs also possible)
Tx - pupil block glaucoma and other acute increased IOP
- immediate lens removal in anterior luxation (rarely luxates posteriorly on own, subluxation may be tx with sx or medically, risk of anterior luxation in subluxation or posterior luxation)
- medical tx necessary to control future IOP spikes.
Medical tx of lens luxation
= Xalatan = latanoprost, a PG analogue
- for posterior luxation to prevent anterior displacement of the lens
- PG causes decreased pressure, marked miosis (due to SMC contraction in CB and iris)
- SID (morning for better miosis)
- BID for maximal miosis
Sx tx of lens luxation
- removal of lens prior to anterior luxation (poor prognosis if anterior luxation and high IOP, guarded/ poor with posterior sub/luxation and high IOP, moderately good to guarded prognosis with p-sub/lucation and normotension)
- remove lens if acutely luxated anteriorly
- control of IOP long-term with drugs if necessary
(possible additional lasering of CB)
What is endolaser cyclophotocoagulation?
coagulation of soft tissue with light as an additional sx management option for lens luxation. You go behind iris, burn CB to decrease risk of glaucoma (not 100% effective but quite good). Up to 30% of CB is intact to avoid hypotony and pthisis (wasting or atrophy of a body part)
3 typical signs of retrobullar disease
- globe displacement (exopthalmos, dorsolateral displacement)
- TE protrusion
- facial asymmetry