Aqueous, Vitreous and Retina Flashcards
Aqueous Humour Functions
3 points
Maintains IOP
Supplies nutrients, removes waste from avascular tissue
Optical clarity
Causes of Glaucoma
- Obstructed aq humour outflow
- Increased IOP too high for optic axoplasmic flow
- Increased vitreous glutamate
- Retinal ganglion cell dysfunction -> optic nerve degen and atrophy
- Luxated lens
Types of Glaucoma
- 2° glaucoma**
- 1° Angle Closure Glaucoma
(PACG) > 1° Open Angle
Glaucoma (POAG) - PACG = F dogs**
What is PACG?
Predisposed breeds
- Bilateral, unilateral1st
Predisposed: - Cocker Spaniel,
- W+E Springer Spaniel,
- Basset,
- Labrador,
- Golden Retriever,
- Husky.
What is POAG?
Predisposed breeds
- Gradual increase in IOP;
simultaneous in both eyes.
Predisposed: - Norwegian Elkhound,
- Beagle,
- Petit Basset
- Griffon Vendeen
Causes of 2° Glaucoma:
- Vitreous prolapse
- Lens luxation
- Intumescent cataracts
- Neoplasia
- Uveitis
- Hyphema
- Pigment deposits
- Phacolytic
- Aphacic
Effects of Increased IOP:
- Buphthalmos
- Haab’s striae = Ruptures
Descemet’s membrane - Corneal oedema (IOP > 40mmHg) * Exposure keratitis
- Mydriasis (Iris sphincter muscle
damage) - Pigment release from
iris - Pars plicata and individual ciliary
processes atrophy
*Closure of the Iridocorneal angle and collapse of the sclerociliary cleft (anterior peripheral senechiae can form)
*Cataracts and lens luxation - Pressure on retina & optic nerve
head - Build up of vitreal glutamate
- Impact on perfusion and axoplasmic flow of optic
nerve axons & retinal ganglion cells
Signs of Acute Glaucoma
- Pain
- Episcleral congestion
- Corneal oedema
- Corneal vascularisation (deep ‘brush-border’ advance ~1mm/day)
- Mydriasis (mid-dilated, unresponsive pupil)
- Optic nerve head swelling +/- h+
- Normal ERG
- Vision loss
Signs of Chronic Glaucoma
*Pain less evident
*Haab’s striae
*Corneal oedema
*Buphthalmos
*Iris atrophy
*Ciliary body atrophy
*Lens luxation /subluxation
*Optic nerve atrophy
*Retinal atrophy
*ERG absent
Glaucoma - Diagnostics
*Ocular exam
*Tonometry
- (Digital)
- Indentation
- Applanation
- Rebound
*Fundoscopy
*Gonioscopy
*ERG
Medical Management of Glaucoma - Dogs
- Xalatan (Latanoprost) - prostaglandin analogue; a powerful antiglaucoma; use as first line treatment (1 drop 3x within the first hour) in acute glaucoma whilst awaiting urgent referral appointment to a veterinary ophthalmologist. (Avoid using in cases with concurrent lens luxation or uveitis, cats)
- Brinzolamide (Azopt) or Dorzolomide (Trusopt) - carbonic anhydrase inhibitors; give even in the case of concurrent lens luxation and cats
- Timolol 0.5% drops - beta-adrenergic blocker. Side effects = miosis, conjunctival hyperaemia, local irritation, bradycardia, hypotension. (Avoid uveitis, anterior lens luxation and heart failure).
- Osmotic diuretics (e.g. Mannitol) - rarely used due to risks, contraindications and practical difficulties.
Medical Management of Glaucoma - Cats
Carbonic anhydrase inhibitors - trusopt
Glaucoma Surgery
- Cyclocryotherapy
- Cyclophotocoagulation
- Enucleation
Vitreal Opacities
Hyalitis - inflam exudates
Synchisis scintillans - liquified vitreous, golden refractile bodies, settle if head is shaken
Asteroid hyalosis - degen disorder - older animals, white refractile bodies, dont settle
Retinal Vasculature - Dog
*Usually 3 or 4 major venules which form a circle (not always complete) on the optic disk surface
*Up to 20 arterioles which may be tortuous
Optic Disc - Dog
*Variable amount of myelin
*Pale pink in colour
*Physiologic pit
*+/- Pigmented ring
Retinal Vasculature and Optic Disc - Cat
*Circular optic disk lacks myelin
*3 major venules leave the disc edge with 3 major arterioles *Tapetum is usually yellow or green in colour
Progressive Retinal Atrophy (PRA) - What
- Hereditary neuroretinal degen
- Autosomal recessive
- Early Onset – dysplasia (rods and
cones)- Irish Setters
- 6-8wks
- Late onset – degeneration (rods and cones)
- Poodles, Spaniels, Labradors
- 3-5yrs
- Poor outer segment
regeneration
Progressive Retinal Atrophy (PRA) - Features
- Tapetal hyperreflectivity
- Pigmentary changes
- Blood vessel attenuation
- Optic nerve atrophy
Progressive Retinal Atrophy (PRA) - Diagnosis
- Thoroughhistory–nyctalopia
- Progressive loss of vision
- Pupillary light reflexes poor
- Fundus examination
- Tapetalhyperreflectivity
- Nontapetalhyporeflectivity * Pigmentary changes
- Bloodvesselattenuation
- Optic nerve atrophy
Progressive Retinal Atrophy (PRA) - Tx
- No true treatment available – genetic disease
- {Antioxidant medication [lutein, xeazanthin, grape seed extract,
lycopene, Ocuglo] sometimes used} - {New technologies – subretinal stem cell implants}
- Homemanagement
- Prevention: BVA/KC Eye Testing Scheme
- Gene mapping–blood testing
Retinal Detachments - Causes
Traumatic - “knocks it off”
Vitreal traction bands - “pulls it off” Serous effusions - “pushes it off”
Retinal Detachment - Types
Non-rhegmatogenous
(Subretinal exudate; No retinal tear present)
Rhegmatogenous = tear in retina
(Hole in the retina through which the vitreous can move)
Retinal Detachment - Diagnosis
- Ophthalmoscopy
- Sometimes it is visible in the pupil w/o ophthalmoscopy
- Ultrasound
