Q. What happens in Age-related Macular Degeneration?

A. The cause of AMD is obscure and probably multi- factorial. Age-associated change typically occurs in the area of the macula, specifically in its outer 2 layers (the photoreceptor and retinal pigment epithelium -RPE) and on a thin membrane (Bruch's membrane) that separates the retina layer from the choroidal layer. All these layers, especially the photoreceptor, aid in the function of the retina to form images. The function of the RPE is to digest the waste product of the photoreceptors and eventually, aid in its transport to the choroidal layer where it is eventually eliminated from the eye. Over a person's lifetime, there is considerable stress on the ability of the RPE to digest the volume of material coming from the photoreceptors. Waste . accumulates in the RPE with increasing age. The ...' Bruch's membrane, the membrane that the waste product has to cross from the retina to the choroid, on the other hand thickens with age especially within the macular area. In time, transport of waste products from the RPE to the choroid is slowed down by these changes in the Bruch's membrane, leading to Drusen formation.

Drusen are the initial clinical fmdings in AMD and are found beneath the RPE. Drusen represent focal metabolic abnormalities of the RPE. With time, the photoreceptor and RPE overlying the Drusen atrophy. The area of atrophy clinically is well- demarcated and allows an enhanced view of the underlying choroidal vessels. This area represents loss of the RPE -photoreceptor complex (DRY TYPE / NON-EXUDATIVE AMD). Occasionally, thickening appears to weaken the Bruch's membrane, predisposing it to breaks and consequently allowing growth of abnormal blood vessels from the choroid onto the macular area (choroidal neovascularization -CNV), and eventually leads to scarring (WET TYPE/ EXUDATIVE AMD).

In DRY AMD, patients have severe, gradual diminution of central vision. In WET AMD, there is a sudden onset of decreased vision, and metamorphopsia (bending of straight line) or miscropsia (objects appear smaller). Symptoms are caused by growth of these abmormal vessels (CNV) appearing as a greenish pigmentation deep to the RPE. Eventual scarring is the main cause of such severe decline in vision for this type of AMD.

Q. Who is at risk in developing Age-related Macular Degeneration? What are the risk factors?

A. The increasing number of patients afflicted with AMD, as well as the difficulty in its treatment, has led to a search for factors that might alter the prognosis if they could be somehow modified. . Several risk factors have been considered in many "- , studies suggesting that AMD is truly of multifactorial etiology. Age, as the name of the disease implies, is one of the risk factors. Aging is a fundamental biological phenomenon that occurs even in the absence of disease. The longer one survives, th~ higher the risk of acquiring the condition. However, it is said that AMD is not inevitable with advancing age. Sex has likewise been incriminated. Some studies say females outnumber males but this just largely reflected the increased proportion of females in the older age groups. Systemic conditions, such as cardiovascular disease and hypertension, have also been implicated. Environmental factors are also widely mentioned. Cigarette smokers are said to have almost three times the risk of non-smokers. There is little evidence that indirect exposure of the eyes to sunlight is related to AMD. Lastly, nutritional factors are also being given significant attention. Antioxidants and zinc are being thought of as agents that appear to retard progression of AMD.

Q. What are the treatment options? Can vision be restored?

A. The severe decline in vision in AMD is primarily related to the development of CNV with outright or subsequent involvement of the clinical fovea. Currently, the only treatment that has been shown to be beneficial based on studies is photocoagulation. However, only a small number of patients with CNV can be effectively treated by such modality. Majority of patients do not meet the criteria set to make laser treatment beneficial at reducing severe visual loss. New treatment strategies are aimed at limiting the degree and extent of destruction of retinal tissue overlying the CNV ~ especially the clinical fovea.

Surgical removal of the CNV (submacular surgery)~ selective destruction of CNV via low- intensity light exposure of tissues treated with photosensitizers to produce photochemical effects . with subsequent preservation of the overlying neurosensory retina (Photodynamic Therapy - PDT)~ radiation therapy ~ and the use of pharmacologic intervention with the advantage of avoiding laser-induced retinal damage~ are all ' options still presently under study with regard to the efficacy in treating AMD~ especially the exudative type. There is no current treatment that restores visual function within areas of geographic atrophy (nonexudative AMD)~ disciform scarring (exudative AMD)~ or photocoagulation (present treatment for CNV).

Q. What assurance / advice can we give patients with Age-related Macular Degeneration?

A. Presently ~ the most important aspect of patient management remains education. Every patient with AMD should be informed that peripheral vision is almost always ret8jned and that the loss of central vision will not result in total physical dependence. Some patients obtain useful vision with telescopic lenses~ special magnirying lenses~ and similar optic aids. Although the proportion of patients who achieve satisfaction is disappointingly small~ every patient should be advised to try these low vision aids before concluding their relative unusefulness. Consultation with low-vision specialists is of the utmost importance in maximizing a patient's ability to use the visual function that he currently retains~ consequently minimizing the associated disability.

For patients with currently monocular involvement~ they should be taught to monitor other eye~s central vision on a regular basis to detect symptoms that may herald the development of the same disease condition. Emphasis on immediate visit to the ophthalmologist must be made once such changes are noted. As some patients may not appreciate such symptoms, bi-annual visit for examinations should be suggested, if not imposed.