The Blind Eye Flashcards
What order are layers of the retina passed through by light, and which direction does the neural stimulus travel?
> Light travels…
- Ganglion cells (ganglion cell axons form optic nerve, layers 8-10)
- Cells in inner retina (layer 5-7)
- Photoreceptors (rods and cones) in outer retina layer 2-4
- RPE outmost layer number 1
neural stimulus travels opposite direction then on to
- optic nerves
- optic chiasm (more decussation in dogs than in cats)
- optic tract
- optic radiation
- occipital lobe of cerebral cortex
What do the outermost and innermost layers of the retina lie next to?
- outtermost next to choroid
- innermost next to vitreous
Which layer is the only non-neural layer?
Number 1 RPE 9retinal pigment epitherluim)
- nurturing layer
Which layer of the retina does glaucoma damage?
Ganglion cells
How may eyelid disease -> blindness?
- severe drooping eg. in sniffer dogs w/heavy ears and foreheads
Tx drooping facial skin -> blindness?
- Stades procedures of the upper eyelid
- reduction palpebral aperture
- facelift (“rhitydectomy”)
Why may severe drooping face not be noticed by owner?
Slips back into place when dog look dorsally
What corneal problems may -> blindness?
> chronic corneal pathology -> - scarring - vascularisation - pigment deposition - KCS - LPI/pannus/EK - sequestra (cats>horses>dogs) - pigmentary keratitis (PUGS) > severe acute disease -> - scarring -ulcerative - KCS related - Traumatic in origin - melting progression d/t severe inflam or infection
What is symblepharon and when is it commonly seen?
corneal problem
> adhesion of conjunctiva onto itself and cornea
- Kittens affected with cat flu esp if when v young (FHV, Bordatella, Calicivirus)
- FHV epithelial tropism -> corneal epithelial depletion and destruction of limbal stem cells -> conjunctiva advancement over cornea
- permenant focal/diffuse scar
- If infected
Tx symblepharon?
Stem cells transplant!!
What is pigmentary keratitis and when is it commonly seen?
corneal problem
> pigment and chronic corneal irritation
- specifically seen in pugs w/entropion (d/t limbus pigmentation)
- lower medial eyelid and medial canthus
- can -> blindness
What are PPMs? Ddx?
Uveal problem
> persistent pupillary membranes arising at iris collarette
- failire of regession foetal BVs
- congenital problem
- strands may span iris-iris, iris-cornea (LEUKOMA) slowly pregressive, iris-lens(CATARACT) usually progressive
- can worsen with age
> Ddx posterior/anterior synechia affecting PUPILLARY iris not iris colarettte
What does the uvea consist of?
- iris: pupil motion, in contact with anterior lens and ICA [iridocorneal angle]
- ciliary body: muscle and epithelium, produces AH and focuses lens
- choroid + tapetum: eeds outer retina that lies on top of it
Which uveal problems may occour?
uveitis
> inflammation -> leakage plasma/blood
- turbid AH (flare) and ventral keratic precipitates
- hypopion (accumulation WBCs ventrally)
- hyphema
- clots in AC +- Vitreous
> muscle contraction
- pain (iris and ciliary body spasm)
- photophobia/miosis
> damaged endothelium -> corneal oedema
> iris adhesions (posterior synechia, anteria synechia and closure of the ICA)
> Development of PIFMs can also clog ICA
> Low IOP (helps distinguish from glaucoma)
What is a potential cause of sudden onset blindness in the cat?
- renal disease -> ^ BP -> glaucoma, hyphema and retinal detachment
- may occour in hours
What are PIFMs?
- preiridial fibrovascular membrane - grows like ivy within eye
- microscopic vascularisation
- d/t chronic uveitis
Can posterior synechia affect vision?
yes cloud the pupil
Which species are most likely to develop 2* cataracts
Cats and horse , less common in dogs
Where do leaks occour w/ retinal detachment ?
between layers 1 + 2
How are cataracts and uveitis related?
> uveitis -> 2* cataracts
- slowly progressive, can beome mature over time
- in cats (sometimes horses and dogs) can -> lens luxation
cataracts -> phacolytic uveitis
- leakage of lens proteins (crystallines) -> aqueous humour
- loss of immune tolerance to naturally encapsulated protein
What is phagoclastic uveitis?
- lens ruptures/breaks
- commonly seen with diabetic cataracts d/t being made of sorbitol which keeps absorbing water
- may be d/t trauma
What type of uveitis are cats and horses commonly affected by?
> recurrent uveitis (ERU/moon blindness/periodic ophthalmia)
- 1* insult eg. Leptospira horses, Toxo/viruses in cats
- breakdown of BOB (blood ocular barrier)
- anamnestic response triggered by epitopes of self antigen
- most recurrent uveitis considered IDIOPATHIC as @ time of investigation 1* cause is no longer present
cataracts and glaucoma
chronic nature
Tx uveitis?
- treat cuase if known
- generally tx symptomatically (Anti-inflammatories)
> Topical (affect ulcer healing and diabetes, but effective) start ^ freq application - prednisolone acetate [god penetration, harsh on ocular surface]
- dexamethasone phosphate [less penetrating, kind to o surface]
- NSAIDs [ do not affect diabetic control but ? efficacy] ketorolac, diclofenac etc.
> Systemic (do not affect ulcer healing provided it is avascular) Antiinflammatory dose, immune mediated may require immunosuppressive dose - posterior uveitis and severe anterior uveitis where topical would be ineffective
- steroid: Pred tablets
- NSAID: Meloxicam, carprofen, flunixin meglumine
Are use of topical steroids in a diabetic post-cataract surgery indicated?
- theoretically no as affect pituitary-hypothalamic-adrenocortical axis
- in practice not that relevant as high doses rarely necessary and taper off quickly
