The Abnormal Size and Position of the Eye Flashcards
What does the prefix phac- pertain to?
The lens
What does the prefix cyclo- pertain to?
Ciliary body
What does the prefix kerat- pertain to?
The cornea
What does the prefix blephar- pertain to?
Eyelid
What does the prefix dacryo- pertain to?
Nasolacrimal system
What does the prefix hyalo- pertain to?
The vitreous
Which species have a closed orbit?
Humans and herbivores
Which species have an open orbit?
Carnivores and pigs
What are the different tissues that fill up the orbit?
Eye
Extraocular muscles
Blood vessels, nerves and connective tissue
Fat
Lacrimal gland, gland of TE and zygomatic salivary gland
What can cause space occupying lesions in the orbit?
Infection or inflammation as abscesses or cellulitis
Neoplasia (normally malignant)
Specific tissue inflammation - extraocular polymiositis
Parasites
What are the clinical signs of space occupying lesions?
Globe displacement
Protrusion of the third eyelid
Change in facial symmetry
What are the characteristics of globe displacement?
Frequently dorsolaterally but depends on position of the mass
Frequent anterior component - exophthalmos
Why does protrusion of the third eyelid (TE) occur with space occupying lesions?
With exophthalmos
Mass displaces orbital fat
Passive third eyelid protrusion
What is microphthalmia?
Small eye
What are the causes of microphthalmia?
Small eye from birth usually bilateral and may be accompanied by other ocular defects
Through destruction of the ciliary body as a sequela to inflammation, pthisis bulbi, targeted surgical destruction or chemical ablation
What is buphthalmia?
Enlarged eye
What causes buphthalmia?
Increased IOP leading to globe stretching and other changes such as conjunctival and episcleral hyperaemia, corneal oedema, Haab’s striae, Zonular tears, corneal ulcer
What is Haab’s striae?
Stretch marks due to breaks in Descemets membrane
What cases zonular tears?
Overstretching of fibres due to lens displacement
Visible lens equator through pupil
What causes glaucoma?
Increased IOP
Damage to the optic nerve head and neural retina
What are the 10 layers of the retina?
1 epithelial
9 neural with rods, cones and ganglion cells
What can cause primary glaucoma?
Inherited
Goniodysgenesis = abnormal iridocorneal angle
What are the two forms of primary glaucoma?
Open angle which is common in people
Closed angel which is common in dogs
What can cause secondary glaucoma?
Blood, fibrin, PIFMs, WBCs, Neoplasia Inflammation - uveitis Hyphema Lens luxation Intra-ocular/metastatic neoplasia Trauma
Which cat breed is predisposed to primary glaucoma?
Burmese
What can cause secondary glaucoma in cats?
Uveitis
FIV, FeLV, FIP, Toxoplasma
Idiopathic
What is the relevance of whether glaucoma is primary or secondary?
Long vs short term - only one eye affected if secondary and once treated medically might not recur
The other eye - primary will affect both eyes at some point, long term monitoring/treatment will be needed
Breeding - no worry with secondary, advise against if primary
What are the clinical signs of glaucoma?
Mid-dilated non-responsive pupil +/- aniscoria
Conjunctival and episcleral vessel congestion
+/- vision problems (negative menace/vision maze test)
High IOP on tonometry
What are the clinical signs of high to very high IOP?
Corneal oedema Haab's striae Cupping of optic nerve head Lens displacement Aphakic cresent Corneal ulceration
What is aphakic crescent?
Crescent shaped gap due to tear of the zonules and lens movement away from it
Development of crescent between pupil and lens
What is the treatment for glaucoma?
Control of IOP using anti-hypertensive drops
If secondary treat inflammation, remove the lens from the anterior chamber surgically, remove the eye with problem tumours
What are the different anti-hypertensive drops that can be given?
Beta-blockers = Timolol
Carbonic anhydrase inhibitors = Dorzolamide
Prostaglandin analogue = Latanoprost
What is the rationale behind using beta-blockers to treat glaucoma?
Reduce production of aqueous
Give BID
Weak but cardiac and respiratory effect
What is the rationale behind using carbonic anhydrase inhibitors to treat glaucoma?
Reduce the production of aqueous
Block CA enzyme in the ciliary body epithelium
Given BID to TID
Strong, work well in combination with beta-blocker (Cosopt)
Works in cats and horses
What is the rationale behind using prostaglandin analogues to treat glaucoma?
Increases the outflow of humour
Given SID in the evenings or BID
Strongest but can cause inflammation
Doesn’t work in cats, works in horses
How is glaucoma managed?
Hospitalisation with serial measurement of IOP every 3 hours to plot a curve
What are the clinical signs of lens luxation?
Phacodeonesis-Iridonesis - lens and iris wobbling Anterior presentation of vitreous Deep anterior chamber Anterior or posterior luxation An increase in IOP
What are the causes of posterior luxation?
Cataract formation
Lens induced uveitis
Lens adhesion to the retina
What are the consequences to anterior lens luxation?
Pupil block glaucoma
Damage to the corneal endothelium - central corneal oedema
Which breeds are affected by inherited lens luxation?
Terrier breeds
Lancanshire heelers, Chinese crested, Australian Cattle Dog, Volpino Italiano
What pathology does pupil block glaucoma and other acute increase in IOP cause?
Damage to retinal ganglion cells
Damage to optic nerve head
Damage to blood vessels possible
What is the treatment for pupil block glaucoma and other acute increases in IOP?
Immediate removal of the lens in anterior luxation
Medical therapy to control future IOP spikes
What is used in the medical management of lens luxation?
Xalatoan - PG analogue (causes marked miosis)
What is the name of the surgical treatment for lens luxation?
Endolaser cyclophtocoagulation
What are the three typical signs of retrobulbar disease?
Displacement of globe, 3rd eyelid protrusion, change in facial symmetry, corneal ulcer
What causes aphakic crescent?
Increased IOP, zonules break, lens displaces, see equator
What test would confirm high IOP?
Tonometry
Is glaucoma painful?
Yes
Does glaucoma affect vision?
Yes as it damages the retina and optic nerve head
What is an IOP curve?
Measurement of the IOP every 3 hours and plotted on a graph to see when it spikes
