Fundus: Macular Degeneration Flashcards
What are the two classifications of macular degeneration?
- ‘Dry’ (non-exudative): slowly progressive deterioration in visual function.
- ‘Wet’ (exudative): when growth of new, abnormally located blood vessels (a choroidal neovascular membrane, or CNVM) underneath (and towards) the retina causes sudden loss of vision, by leakage of fluid or by haemorrhage.
Dry may progress to wet.
What sort of blindness does macular degeneration cause, and what are some other names of macular degeneration?
Loss of central vision only (central scotoma), with difficulty reading and with recognising distant objects. Thus peripheral vision, important for navigation, is retained. For this reason, sufferers are generally able to maintain an independent lifestyle. Bilateral, may be asymmetric.
The condition is also known as ‘SMD’ - senile macular degenerstion, or ‘AMD/ARMD’: age-related macular degeneration.
What is the principle pathological feature of dry macular degeneration, and where is it deposited?
The presence of drusen, deposited between the retinal pigment epithelium (RPE) and the underlying Bruch’s membrane.
Order of layers: choroid, Bruch’s membrane, (Drusen), RPE, rods and cones.
What are two other pathological features occurring in dry macular degeneration?
- Atrophy of retinal pigment epithelial (RPE) cells
- Degenerative change in photoreceptor outer segments.
These changes (along with drusen deposition) are concentrated at the mscula, hence the name of macular degeneration.
What is the visual disturbance in wet macular degeneration?
An often sudden, profound central visual loss.
Or, if retinal function is maintained, central distortion of straight lines instead of visual loss: doorways and reading print seem to bend.
Ergo: If the process occurs eccentric to the fovea, these symptoms may be appreciated as off-centre (this ‘distortion’ loss of vision is the only type of ARMD which may be amenable to treatment by laser).
How do drusen appear on fundoscopy?
Drusen are small, discrete yellowish deposits commonly seen at the macula after the age of 45 years, but they are usually asymptomatic. With increasing age, their size and number increase. The macula becomes mottled due to atrophic pallor and reactive hyperpigmentation. Even at this advanced stage, clinical appearances correlate poorly with measured visual acuity.
How would a choroidal neovascular membrane (CNVM) appear on fundoscopy compared to drusen?
A CRVM may appear similar, but is often accompanied by haemorrhage and leakage of serum, seen as exudate.
Since this process usually occurs in a centrifugal fashion, the result is often a disc-like lesion with haemorrhage, drusen and RPE atrophy/hyperplasia at the centre, and exudate and haemorrhage at the periphery. Later, spontaneous involution occurs, leaving a large scar and severely impaired function.
Which four main symptoms should be verified on history in macular degeneration?
- Blurred central vision
- Preservation of peripheral vision
- Distortion of straight lines (Amsler grid test)
- Near vision more impaired than distant vision
Examination of macular degeneration? Three main points.
- Visual acuity (near and far); Amsler chart
- Testing pupil reactions (usually normal)
- Dilated fundoscopy
Main investigation of macular degeneration?
Fundus fluorescein angiography is imperative when treatable choroidal neovascularisation is suspected. FFA may demonstrate abnormal fibrovascular tissue, leakage or pooling of dye.
Treatment of macular degeneration?
Active medical intervention is rarely possible.
Counselling - emphasise peripheral vision is retained.
Refraction - incl. low vision aids to maximise remaining functiin.
Registration as blind or partially sighted may be appropriate.
Laser photocoagulation of neovascular membranes is useful in selected cases, particular when the site is away from the centre (fovea) of the macula.
