7.2 Common eye diseases Flashcards
Define visual impairment
Any diagnosed condition of the eye or visual system that cannot be corrected to within normal limits
What are the most common causes of reading difficulty?
Refractive error
Cataract
Macular degeneration
Glaucoma
What is the most common eye disease in Australia?
Cataracts
What is cataracts?
a loss of transparency of the lens
What is a nuclear cataract and what will it cause?
Hardening of the core of the lens that expands through the layers
Causes reduced transmittance of light (esp blue), increased scatter and increased fluorescence. Things will appear more red and blurry
What are cortical cataracts?
Changes to the lens proteins that start at the margin of the lens, and spread through the more superficial layers towards the optic axis
What are capsular cataracts?
Modification of the lens capsule anteriorly or posteriorly which can occur subsequent to eye surgery
Who is more likely to have cataracts and why?
ATSI people (3 x more likely) Barriers to treatment, lack of health service, ignorance of cause, fear of surgery, difficult to access treatment as a public patient
What is glaucoma?
A collection of disorders characterised by progressive loss of ganglion cells (GCs) and their axons (optic nerve)
What is the second leading cause of blindness in the world?
Glaucoma
What happens in increased IOP glaucoma?
The increased IOP in the anterior segment is transferred posteriorly through the vitreous. Pressure distorts the sclera at the lamina cribrosa, compressing the ganglion cell axons leading to GC death
What causes GC loss in glaucoma?
Decline in the retrograde supply of neurotrophins to GC from their axon terminals
Release of excitotoxic amino acids by damaged GC cells
Apoptotic cell death
Why does glaucoma present late
Tends to first affect peripheral vision ad these losses are compensated for by eye movements so go unnoticed
What will be the appearance of the optic disc in glaucoma?
The margin appears eroded, often inferiorly
The disc appears enlarged and the area of pallor increases
The normal hallow cupping of the disc increases over time with progression of the disease
What is closed angle glaucoma?
Pressure on the posterior aspect of the iris causes the iris to buckle, compressing the trabecular meshwork and restricting the drainage of the aqueous humour
What is open angle glaucoma?
The trabecular meshwork and drainage network can become clogged and restrict the passage of aqueous humour
What causes the changes on the disc and fundus?
Associated with progressive visual field loss, due to death of ganglion cells, resulting from compression of their axons
What happens in macular degeneration?
There is a loss of central vision due to degeneration of the photoreceptors, specifically those in the macular region
What will you see in dry AMD?
Drusen/white spots
Areas of cell loss, centred on the macula
What are the principle cell types affected in AMD?
Light sensitive photoreceptors and their supporting pigmented epithelial cells
What are the signs of emergent AMD?
Sub retinal deposits which prevents oxygen filtration to the photo receptors
Pigmentary disturbance
Drusen
what is the histopathology in dry/non-exudative AMD?
Loss of photoreceptors and RPE cells in the macular regions
Accumulation of leucocytes in the choriocapillaries
Sharp transition into histologically normal photoreceptors
What is the histopathology of wet/exudative AMD?
Breakdown of Bruch’s membrane by phagocytic cells
Sprouting of choroidal vessels which breach Bruch’s membrane and often the RPE
Choroidal neovascularisation of the retina
New choroidal vessels leak serum constituents and blood cells into outer retina promoting retinal dysfunction and loss of vision
Bleeding into retina proper
What increases the risk of AMD?
Smoking
High fat and cholesterol
What decreases the risk of AMD?
Hight fatty acid intake
Eating fish 1/wk
What are the 2 genetic loci associated with AMD?
1q32 complement factor H
10q26
What is the clinical diagnosis of AMD?
Recognition of end state degeneration of neural tissue
