Ophthalmology: Fundus Orbit Globe Flashcards
What are the two layers of the retina?
Neuroretina and Retinal pigment epithelium
What is the function of the retinal pigment epithelium?
- Lies outside the neuroretina
- Pigmented monolayer
- Responsible for phyagocytosis of discarded discs from rods
- Delivery of nutrients to photoreceptors
- Lacks pigment where it overlies the tapetum- allowing light passage
What is the choroid?
What is the tapetum?
Choroid- Very vascular pigmented later between the RPE and sclera
Tapetum- highly light-reflective layer which aids vision in low light conditions
What is the sclera?
The outer fibrous ‘coat’ continuous with the cornea
Consists of mostly collagen
‘Perforated’ at the most posterior pole- optic nerve axons
- What is the function of the tapetum?
- How does the tapetal fundus apear ophthalmically?
- Reflects light which has passed through the retina back onto the photoreceptors for additional stimulation
- Roughly triangular, dorsal to the optic disc. (yellow/green/orange/blue)
Grey in puppies (underdeveloped)
Retinal blood vessels against a background of tapetum (RPE lacking pigment)
How does the non-tapetal fundus appear ophthalmically?
- Varies in colour grey to dark brown
- No tapetum, RPE pigmented
- Retinal blood vessels against a background of RPE and choroidal pigment
- If RPE unpigmented then retinal vessels are against choroidal vessels- orange
How does the optic disc appear ophthalmically?
- Circular but varies because of variable myelination
- 3-5 major veins at the edge
- Some dogs have hyper-reflective crescent around the disc where retina is thinner
What are ophthalmoscopic abnormalities?
- Tapetal hypereflectivity
- Acquired pigment in the tapetal fundus
- Vasculat attenuation
- Haemorrhage
- Retinal detachement
- What causes tapetal hyperreflectivity?
- What causes acquired pigment in tapetal fundus?
- What does vascular attentuation occur secondary to?
- Retina is atrophic the tapetum is seen through a thinner layer then normal- brighter
- Melanocyte proliferation and migration- non-specific changes (inflammation etc)
- Secondary to retinal degeneration- metabolic demands has mass decline
How does haemorrhage of the retina appear ophthalmically?
- Sub-retinal haemorrhage appears as small dark round spots
- Superficial retinal haemorrhage is streaky and radial- follows nerve fibre later
- Pre-retinal haemorrhage settles under gravity and assumed a boat shape
- Where is the neuro-retina ‘firmly’ attached?
- Where does retinal detachment occur?
Optic disc and ora ciliaris
What is the BVA/KC/ISDS eye scheme?
Certify pedegree dogs free of hereditary eye disease
- What is usually the first sign of generalised progressive retinal atrophy?
- What are the later stages?
- What is the earliest ophthalmic stage?
- Night-blindness, fear of the dark
- Cataracts, total blindness
- Hyperreflectivity followed by vascular attenutation
Ultimately no functional retina persists
What is collie eye anomaly?
- Common congenital lesion
- Hypoplasia and hypopigmentation of the RPE and choroid
- Area lateral to the optic disc
- Pale patch with abnormal choroidal vessels against the white of the sclera
Very few dogs blind
Some flat detachment, others extensive retinal detachments which interfere
Non-progressive
What diseases casue retino-choroiditis?
How does it appear?
- Distemper
- Toxoplasmosis
Circumscribed grey dull areas as a result of oedema and inflammation
In time the retina is destroyed giving circumscribed areas of hyper-reflectivity
What conditions can cause retinal haemorrhage?
- Coagulopathies
- Hypertension
- Septicaemia
- Hyperviscosity
- Leukaemia
- Trauma
- Sometimes in associated with retinitis
- Retinal detachment
What are the DDX for retinal detachment?
- Idiopathic/steroid
- Retinal dysplasia
- Hypertension
- Collie eye anomaly
- Loss of vitreous support
- Trauma
- Traction detechments
- Rhegmatogenous
What is SARD?
Sudden acquired retinal degeneration
* sudden total loss of retinal function
* Cause assumed to be toxic
No treatment
Total blindness
What disease causes a small dark disk with usually normal calibre blood vessels and a normal retina?
Optic nerve hypoplasia
Congenital blindness- rare
What disease casues oedmatous swelling of the optical disc as a result of raised intracranial pressure, hypertension or pressure due to a tumour?
Papilloedema
* Disc appears swollen with an indistinct outline
What is optic neuritis?
How is it treated?
Inflammation of the optic nerve- appears similar to papilloedema
* Sudden loss of vision with fixed dilated pupils
Tx- high doses of systemic steroids for several weeks- only effective if started early
What causes optic atrophy?
Advanced retinal degeneration or sustained glaucoma
Disc appears small and pale or dark
What does the orbit contain?
- Eye
- Optic nerve
- Lacrimal gland
- Extraocular muscles with associated nerves and BVs
- What makes up the rostral margin of the canine orbit?
- What enclose the optic nerve in the orbit?
- bone (zygomatic arch/frontal) for 3/4, completed by the orbital ligament
- Extraocular muscles enclose the optic nerve and form a cone
What are the clinical signs of orbital disease?
- Exophthalmos
- Protrusion of the nicitating membrane
- Strabismus
- Orbital swelling
- Cojunctivitis/chemosis
- Lagophlathalmos
- Pain of difficulty opening mouth
What are differentials for retrobulbar swellings?
- Retrobulbar abscess/cellutitis
- Retrobulbar neoplasia
- Masticatory myositis
How should orbital disease cases be clinically examined?
- Examine eyes in front and above
- Exophthalmos is more striking from above than infront
- Retropulsion gently
- Radiography- bony involvement
Exophthamos with deviation of the globe indicated a focal mass such as a tumour
- What causes retrobulbar abscess
- What is the usual history and clinical signs?
- How is it treated?
- Orbital infection- penetration to skin (FB) or extension from tooth root infection/sinus- idiopathic also
- Sudden onset of pain, swelling, exophthalmos, pain and difficulty in opening the mouth and reluctance to eat- globe signs are secondary
- High doses of broad spectrum ABs and maintain for 3-4 weeks- cornea may well need lubrication
What are the clinical signs of retrobulbar neoplasia?
Exophthalmos with deviation of the globe
Always check nasal air-flow for evidence of nasal neoplasia extending
CT for definitive diagnosis
How should enophthalmos be treated?
No treatment required
Could be horners
What is phthisis bulbi?
How is it treated?
- Refers to an acquired atrophic end-stage eye
- Severe intra-ocular pathology is always implied
- Changes are irreversible and untreatable
- What can cause prolapse of the globe?
- What happens to the eye after prolapse?
- How should it be treated?
- RTA, trauma
- Tractino on optic nerve, immediate oedema of conjunctiva and blobe, lids go into spasm
- Attempt should be made to replace immediately (gentle pressure, wet cottong wool)
Cornea with copious lubrication
If cannot replace- surgery
How should a globe be replaced surgically?
- Lateral canthotomy or use of allis tissue forceps on the lid margin
- Once reduced suture eye lids for 14 days
- Suture material not in contact with cornea
Prognosis of eye guarded
What is meant by buphthalmos?
Pathologically enlarged eye as a result of glaucoma
Implies severe irreversible damage and a blind eye
Describe the process of enucleation
- Clamp/suture lids
- Manoevre eye- do not pull
- Make an encircling incision through the full thickness of the skin
- Cut the canthal ligaments at an early stage
- Work close to the sclera- cut attachments
- Unusual to see the optic nerve
- Place a secure continuous suture in the tissue deep to the lids
