Age-Related Macular Degeneration (Lecture) Flashcards
What drug is used to dilate the pupil? How does it act? Why is it used?
Tropicamide - a short acting muscarinic antagonist.
It blocks the parasympathetic NS which normally constricts the pupil.
Used to make it easier to see the back of the eye with an opthalmascope.
How does the sympathetic NS act on the pupil?
The adrenergic sympathetic NS dilates the pupil.
Define metamorphosia?
Distortion of vision - straight lines appear wavy and areas may be missing.
What is the fovea?
An area in the centre of the macula which has fewer layers as it doesnt have bipolar and ganglion cells. Here light falls directly on photoreceptors and there are no vessels - so vision is very clear.
How does the fovea receive O2 and nutrients?
Gets everything it needs from the underlying well vascularised choroid.
Where is the retinal pigment epithelium found?
Between the choroid and retina.
What is the function of the RPE?
Keeps the retina attached.
‘Renews’ the photoreceptors as they phagocytose the photosensitive pigment when it is worn out and decaying.
Name the 2 types of Macular Degeneration?
Exudative
Atrophic
Describe atrophic macular degeneration?
Atrophy of the RPE occurs and photoreceptors can no longer function.
Slower onset.
Blurred vision.
Describe exudative macular degeneration?
Photoreceptors produce photo-sensitive pigment and when it becomes old it is removed by the RPE.
The RPE isn’t 100% effective and end-products accumulate between the RPE and Bruchs membrane and becomes ‘Drusen’.
Drusen breaks through Bruch’s membrane and new blood vessels grow from the choroid, but they do not have tight junction in their endothelium and are fragile. Vessels rupture and release fluid and fatty exudates. The oedema causes the retina to be deprived of oxygen and nutrients.
New vessels growth is accompanied by fibroblasts which eventually form a fibrovascular scar under the retina.
Rapid onset.
Get metamorphosia.
Why does metamorphosia occur?
Caused by fluid from leaking vessels bursting through Bruch’s membrane and pushing photoreceptors so they are not aligned and the brain produces a distorted image.
What is visual acuity?
Distance in metres at which chart is read/Distance which it should be read.
What is normal visual acuity?
6/6
What is the minimum visual acuity required for driving?
6/12
How do you measure visual acuity?
Check if they need glasses for distance.
Test one eye at a time by covering the other eye.
If vision not perfect, use pinhole. If pinhole helps, the issue is just that they need glasses.
If vision is less than 6/60, stand closer to the chart (5/60, 3/60 etc).
If still cant see top letter on chart at 1/60, count fingers, hand motions, response to light.