AMD and retinal dystophys Flashcards
Name RFs for Dry AMD
- Age
- HTN
- Smoking
- Female
- High fat and cholesterol intake
- Blue iris and abnormal skin sensitivity
Where are drusen located?
Between cell basement membrane and Bruch’s membrane
How do Hard drusen appear?
Small and well defined
How do soft drusen appear?
Larger than 63um and ill defined borders
- Can increase in size and number with age
Are hard drusen or soft drusen a risk factor for Advanced AMD?
Soft drusen
What is geographic atrophy?
Atrophy of the RPE
What is seen in histology of the macula in dry AMD?
- Atrophy of photoreceptors over well defined eosiniophillic mounds in the RPE (hard drusen) and more linear bands in diffuse drusen
- Bruch’s membrane thickened or calcified
- Choriocapilaries occasionally replaced by degenerative fibrosis
What is a basal linear deposit?
Deposits between the RPE cell membrane and its basement membrane
- Linked with Start of neovascularisation or wet AMD
What are basal linear deposits associated with?
Start of neovascularisation or wet AMD
What is disciform degeneration?
The RPE undergoes fibrous metaplasia with deposition of collagen - causes a disc shaped mass beneath the macula
What is the normal age of onset of retinitis pigmentosa?
Early adult life
What are the possible modes of inheritance of Retinitis pigmentosa (in order of commonness)
- AD: most common
- AR: less common
- X-linked recessive: least common
What mutations are associated with the AD form of Retinitis pigmentosa?
- Gene coding for rhodopsin - on long arm of Chromosome 3q
- Peripherin: On chromosome 6p
Which forms of Retinitis pigmentosa has the best and worst prognosis?
AD - best
X-linked - worst, may result in complete blindness by 3rd or 4th decades
Name symptoms of Retinitis pigmentosa
- Night blindness
- Progressive visual field loss from periphery towards posterior pole
- At endstage - retinal function is limited to central macula –> ‘tunnel vision’
What is seen on fundoscopy in Retinitis pigmentosa?
- Retinal atrophy
- Narrowing and opacification of retinal vessels
- Mixed, coarse strands of pigmentation
What is seen histologically in Retinitis pigmentosa?
- Outer nuclear layer at the fovea appears as a single layer of cells with stunted photoreceptors
- Towards the periphery, the outer nuclear layer is replaced by Muller cells, which fuse with RPE
- RPE cells react by proliferation and migration into the retina to become distributed around the hyalinized vessels –> giving bone spicule appearance
How is Best’s disease inherited?
AD
What is seen on examination in Best’s disease?
Disc of yellow tissue at the macula
Loss of central visual acuity
What is seen histologically in Best’s disease?
Lipofuscin accumulation in RPE cells
Atrophy of photoreceptor layer
What is the inheritance of Stargardt’s disease?
AR
Which gene mutation is associated with Stargardt’s disease?
ABCA4 or ATP binding cassete (also known as STGD1) on chromosome 1p21
Describe the pathophysiology of Stargardt’s disease?
ABCA4 gene mutation leads to abnormal transport of metabolites across the photoreceptor disc membrane –>accumulation of lipofuscin in rod and cone disc spaces
–> RPE and photoreceptor destruction
What % of ARMD patients also have ABCA4 mutations?
18.7%
