Definition:
AMD is a triad of :
1. Decreased visual acuity
2. Stereotyped findings on ophthalmoscopy: Drusens +/- geographic atrophy of the RPE
3. Age > 50 years
The finding of drusens alone with no decrease in vision might be a sign of aging and is not
considered as AMD
Epidemiology:
It is the leading cause of irreversible severe visual loss in people above the age of 60 in 
the western hemisphere.
Prevelance: It affect 11% of patients who are between 65 and 75 years of age, 
and 30% of people older than 75 years.
It is usually bilateral, but may not be symmetrical.
Pathophysiology:
Drusens are thought to be by-products of the Retinal Pigment Epithelium (RPE) which
couldn't be cleared and recycled. They accumulate in the Bruchs membrane just underneath the RPE.
They appear as yellow excrescences in the posterior pole on ophthalmoscopy.
Drusens are rarely seen clinically before 45 years, but they are universal after age 60.
Drusens can be classified according to their consistency into hard, soft, mixed, nodular, and calcified.
Hard drusens are sharply demarcated yellow excrescences whereas soft ones are confluent and have
fluffy borders.

Fig. 1: Drusens in the posterior pole

Drusens can lead to atrophy of the overlying RPE and photoreceptors subsequently.
It also produce "cracks" in the Bruchs membrane that allow choroidal vessels to grow in the
sub-retinal and sub-RPE space: the so called Choroidal Neo-Vascular Membrane(CNVM)

Fig. 2: CNVM causing a macular scar

Classification:
1. Non-exudative: 90%
2. Exudative: 10%
        -Defined by the presence of a CNVM
        -88% of legally blind AMD patients
        -CNVM can sometimes be suspected by the Amsler grid test
Natural History:
Non exudative AMD follows usually a relatively benign course.
Exudative AMD entails an aggressive course. 60% of patients with an  occult type of CNVM
might lose 6 lines or more within a year.
Treatment:
Many modalities of treatment have emerged in the past decade.
1. Observation
2. Photocoagulation of the CNVM.
         -This procedure is mainly performed for extra or juxta-foveal CNVM and not for foveal,
because it produces a retinal scar.
3. Photodynamic Therapy
         -Consists of injecting a dye that concentrates in the CNVM, and can be activated at a certain 
wavelength, releasing free radicals that wound scavenge the CNVM without harming the overlying 
retina. The problem with this newly emerging technique is  a high degree of recurrences.
4. Transpupillary Thermal Therapy
         -A known technique that used to be applied for choroidal melanoma, newly introduced in 
the treatment of CNVM. The principle behind it is to deliver thermal energy absorbed by the 
choroidal vasculature, but not high enough to be absorbed by the retinal structures.
         -This fascinating low-cost modality is currently under scrutiny. Large randomized studies 
should be undertaken to verify its effectiveness and safety.