The vitreous and fundus Flashcards
What is the vitreous
The vitreous is an elastic hydrogel that occupies the posterior segment of the globe
- it is composed of 99% of water with the remaining 1% largely mage up of collagen fibers, hyalocytes and hyaluronic acid
What are the role of the vitreous
The vitreous is transparent to enable transmission of light and it provides support to the globe and intraocular tissues
- the anterior vitreous supports the lens
- the posterior vitreous helps maintain close contact of the neurosensory retina with the retinal pigment epithelium
What is the fundus
The fundus can be defined as the posterior region of the eye that is viewed via the pupil during ophtalmoscopy
It always includes:
- the retina
- optic nerve
- choroid
What is the anatomy of the retina
The retina is composed of ten layers and is divided into the inner, sensory retina and the outer, nonsensory retina
The inner retina is composed of nine layers with the photoreceptors (rods and cones) located outermost
The retinal pigment epithelium is the outermost layer of the retina, is nonsensory and is immediately adjacent to the choroid
What is the role of cones
Cones are responsible for visual acuity and color detection
What are the main causes for retinal dysplasia
Retinal dysplasia is uncommon but can have a number of causes
The most commonly cited cause in cats is intrauterine infection with feline leukemia virus or feline panleukopenia virus
Inherited retinal dysplasia is not well characterized in cats but is seen occasionally
- a rod-cone photoreceptor dysplasia leading to retinal degeneration has been documented in the Abyssinian
- optic disc hypoplasia and optic disc aplasia are uncommon
What are the earliest clinical signs detectable on fundoscopy indicating hypertensive retionpathy
The earliest detectable signs of hypertension on fundoscopy are tortuosity of the retinal arterioles and retinal edema with focal bullae
What fundic modification accompanies severe hypertensive retinopathy
More severe disease is associated with hemorrhage and, depending on which vessels are involved, focal hemorrhages may be:
- subretinal
- intraretinal
- preretinal
What is the typical presentation of a cat with hypertensive retinopathy
Acute blindness associated with total retinal detachment with varying extents of anterior and posterior segment hemorrhage
What is the prognosis for retinal detachment
If treatment is instigated early, then even very large retinal detachments can resolve and vision be restored, but this does depend on the extent of the initial damage to the retina
What are the characteristics of diabetic and megestrol acetate retinopathy
Diabetic retinopathy is not well characterized in the cat
The ophtalmoscopic signs are identical to those of hypertensive retinopathy and thus are more likely explained by systemic hypertension rather than glycemic status per se
What are the characteristic of anemic retinopathy
In its mildest form, anemic retinopathy appears as a relative pallor of the retinal vessels
Profound anemia, with hematocrit less than 10% and hemoglobin concentrations less than 5g/dL, is associated with retinal hemorrhages
- it is thought that anemia leads to hypoxic damage of the vascular endothelium with resultant fragility of the vascular walls
What are the fundoscopic signs of active chorioretinitis
Fundoscopic signs of active chorioretinitis include:
- edema
- exudates
- cellular infiltrate
- hemorrhages
- when inflammation is severe, retinal detachment often ensues
What are the documented causes of feline retinal degeneration
Documented causes of feline retinal degeneration include:
- inherited dysplasias and dystrophies
- nutritional imbalances
- drug toxicities
- inflammation
What are the key features for photoreceptor dysplasia
An inherited abnormality of rod and cone development which leads to their degeneration prior to maturation has been reported in the Abyssinian
- this cone-rod dysplasia is inherited in an autosomal dominant fashion
- it is caused by a single base pair deletion in the CRX gene
The disease is very early in onset and the cones appear to be affected before the rods
- the tapetum appears dull with lack of detail from approximately eight weeks of age
- more advanced signs of retinal degeneration progress rapidly
- tapetal hyperreflectivity
- nontapetal depigmentation
- vascular attenuation
What is photoreceptor degeneration
This is a later onset photoreceptor degeneration which is inherited in an autosomal recessive fashion in the Abyssinian
the disease is also described in Somalis, Persian and Siamese
Disease onset occurs from around 18 months of age
- typical signs of advanced degeneration are usually present by 4-6 years of age
