Seminar: Abnormal Size/Position of the Eye Flashcards
What 3 sources of space occupying lesion may -> exopthalmus?
- infection/iniflammation/abscess/cellulitis
- neoplasia
- specific t issue inflam (eg. myositis)
3 clinical signs assocciated with space occupying lesions in the orbit?
- globe displacement (usually dorsolaterally) + exopthalmus
- protrusion of the TE
- change in facial symmetry
What specific tissue inflammation may -> exopthalmus? What other CSs may be seen concurrently?
extraocular muscle polymyositis
- acute 1* inflam (autoimmune)
- thickening of muscles presses on optic nerve -> abnormal PLR
Causes of micropthalmus?
- congenital (from birth, usually bilateral, +- other ocular defects eg. cataracts, rarely very sriking)
- destruction of the ciliary body (cyclodestruction)
> as a sequalae of inflammation, called psthisis Bulbi (severe uveitis), targetted surgical destruction (excessive laser cytoablation) or chemical ablation (gentamycin -> vitreous cavity, not nice!)
Which segment of the eye determines IOP?
Anterior chamber despite being much smaller
What is bupthalmia? Cilnical signs?
= hydropthalmia
- enlarged globe d/t glaucoma (1/2) streatching globe
- conjunctival and episcleral hyperaemia/congestion
- corneal oedema (dmaage to endothelium)
- Haab’s Striae (stretch marks d/t breaks in Descemet’s membrane)
- Zonular tears (overstretching of fibres - lens displacement) - Visable lens equator through pupil (Aphakic crescent = “no lens” crescent)
- Corneal ulcer d/t mild/moderate corneal overexposure
How may glaucoma affect the retina?
- damage to neural retina and optic nerve head
What types of glycoma are possible?
1*
> inherited
- breeding advice?
- very complex (cf. GPRA simple recessive allele)
> Goniodysgenesis
- abnormal formation of the iridocorneal angle
> 2 forms:Closed angle (rapid onset, most common in dogs), Open angle (insiduous onset, most common people)
2*
> anything blocking ICA
- uveitis/t cataracts/infectious caues eg. FIP, Leishmania etc. (protein - ICA synechia, iris thickened)
- Hyphema
- PIFMs
- Neoplasia
- Trauma
- lens luxation
How does closed angle goniodysgenesis present?
1 eye affected initially, within 6 months other one will be too
- IOP >40
- tx prophylactically?
What is visualisation of the iridocorneal angl called?
gonioscopy
How does glaucoma present?
- episcleral and conjunctival hyperaemia
- corneal oedema (d/t endothelial/epithelial causes: fluorocin and IOP to differentiate )
- Anisocoria (d/t likely slightly differnet pressures) and fixed, mid dilated pupil d/t pressure crushing optic nerve etc.
- ^ IOP -> Haab’s Striae if IOP >60ish
+- vision problems (menace/vision maze test) - corneal ulcer d/t exposure
- cupping of optic nerve head
- lens displacement -> overstratching and tearing of zonules, Aphakic cresent formation
What causes glaucoma in cats most commonly?
> 2* to uveitis - FFFT
- FIV, FeLV, FIP, Toxoplasma
- idiopathic
1* form exists in Burmese but much less common
How does differentiating 1* v 2* affect prognosis or decision making?
> if 2, possible only ne eye will be affected
- might lose affected eye/treat and prevent re-occurence
- no need to worry about breeding (unless caused by lens luxation)
1 glaucoma will affect both eyes over time FO SHO
- long term monitoring and tx of 2nd eye necessary- breeding advice necessary
Treatment of glaucoma? MEMORISE!!
- control IOP
> B-blockers
> Carbonic anhydrase inhibitors (active production of aqueous humour in ciliary body epithelium)
> PG analogues (inflame the eyes to cause v pressure, v. low conc needed to prevent iris spasm, also causes eyelash growth and hyperpigmentation) - If 2*, remove cause if poss
> treat inflam
> surgically remove lens from anterior chamber
> remove eye if neoplastic
Why are b-blockers used to control glaucoma? Eg. drug?
> eg. timolol
- reduce production of aquous
- weak but cardiac and resp effec in smallies
Why are carbonic anhydrase inhibitors used to control glaucoma? egs.? What can they be given in combo with?
- eg. dorzolamide- v productin of aqeous
- strong and work well in combo with b blockers
- work well in cats and horses
Why are PG analogues given to control glaucoma? eg.? What conc is needed? Which species are not affected?
> eg latanoprost
- ^ outflow of humour
- strongest, need v low conc (can cause inflammation!)
- Does not work in cats
- WOrks in horses
What are IOP curves? How regularly should they be tested?
Remember IOP changes over time so may be some periods of high and low pressure
- test q3hours
What are phacodonesis and iridodonesis?
- phacodonesis = lens luxation
- iridodonesis = iris movement
> often occour together d/t zonule breakdown and lens subluxation (1* stage of lens luxation)
> seen as wobbly iris when eye moves (video of black and tan dog in lect)
In which breeds is lens luxation inherited?
Terrier + others (lancashire heeler, chinese crested, australan cattle dog, volpino italiano)
- genetic mutation recently identified
- test developed by AHT
> other breeds = spontaneous
What is anterior presentation of the vitreous and when does it occour?
lens luxation allows vitreous to leak forward
- appears as mucous like strand floating in AC
- can block ICA and ^ OP -> glaucoma
= PUPIL BLOCK GLAUCOMA
- v. quick onset (mins/hours)
Which directions may the lens luxate? Which is better prognosis - outcomes? How woul this be seen clinically?
- anterior and posterior
> posterior better - seen as a “deep” AC as lens is no longer holding iris forward
- can lead to cataract formation, lens induced uveitis, lens adhesions to the retina (as it floats around the vitreous)
> anterior - causes pupil block glaucoma
- whole lens visable in AC with pupil seen behind, distorted
- cornea also damaged
What may pupil block glaucoma and other acute ^IOP cause?
- retinal ganglion cells (axons form optic nerve)
- optic nerve head (axoplasmic flow)
- damage to BVs
Tx pupil block glaucoma or any other rapid ^ IOP?
> anterior luxation
- immediate removal of the lens
rarely luxates posteriorly on its own
subluxation can be treated medically/surgically
medical tx necessary to control future IOP spikes
