Macular degeneration is an eye disorder characterized by a number of conditions negatively affecting the macula.
The macula is also known as the ‘yellow spot’ - a miniscule, specialized region of the retina containing photoreceptor cells (cone cells) responsible for central sight in conditions of bright lighting in order to distinguish fine detail and color.
Flanking the central macula is the peripheral macula which is composed of other photoreceptor cells (rod cells) responsible for sight in dim lighting outside the main line of sight.
The major result of AMD is the loss of central vision, the consequences of which are:
- Decreased visual acuity – the loss of fine detail make reading and driving difficult.
- Decreased contrast sensitivity – distinguishing between objects is harder.
- Visual distortion – this makes recognizing facial features difficult and straight lines appear wavy.
- Night glare – this is sensitivity to bright lights at night.
- Blind spots – these appear in a person’s central field of vision, progressively increasing in size if left untreated.
Two forms of AMD have been categorized:
Dry (non-neovascular)
This is the most common form of AMD. It appears to occur due to the specific breakdown, thinning and aging of retinal epithelial cells of a specialized region of the retina called the macula.
This form of AMD occurs gradually over time and is also called atrophic MD because it is characterized by the death (atrophy) of macular cells.
Wet (neovascular or exudative)
While rarer than dry AMD, this form is both more rapid and severe. In fact, a person’s central vision can deteriorate in a matter of days if left untreated.
In this form of AMD, the retinal pigment cells degenerate and new blood vessels grow from those in the choroid (choroidal neovascularization) in order to resolve the problem. However, these newly-formed vessels grow in the wrong place are fragile and tend to leak blood and fluid which can cause scarring in the macula eventually.
Treatments
Treatments have been developed to prevent the progression of wet but not dry AMD. These treatments include:
Photodynamic therapy
This involves the injection of a medication (Verteporfin) into the bloodstream and the shining of a low-power laser to the center of the macula which activates the compound. The medication then detects and attaches itself to the newly-formed (and abnormal) blood vessels to destroy them without damaging the surrounding macular tissue. Repeated treatment might be necessary if the abnormal blood vessels reopen with time.
Anti-VEGF therapy
This involves the intraocular administration of anti-VEGF medication (eg. Ranibizumab, Bevacizumab). Anti-VEGF medication prevents the formation of the new abnormal blood vessels which is normally induced by VEGF (vascular endothelial growth factor) by blocking its vessel-formation action. Repeated treatment may be suggested for prolonged benefits to be achieved.
Laser Treatment
This is less commonly performed than the aforementioned treatment methods. It utilizes a high energy laser beam focused on the retinal area with the newly-formed abnormal blood vessels. This isn’t always effective and repeated laser treatment may even be required again after 3-5 years.
Regular monitoring of patient vision is also suggested - the Amsler Grid test can indicate if you see straight lines as wavy or if you do not even see them (both of which are indications of AMD).
References:
Further Reading
Advanced imaging reveals hidden vision loss in AMD