5.3  Visual Changes in Patients with Advanced Macular Degeneration

Unlike RP, patients with macular disease experience visual loss within the central field of vision, and generally have preserved peripheral vision throughout the course of the disease. The most common type of advanced macular degeneration is that associated with age-related macular degeneration (AMD). Two types of advanced AMD lead to loss of central vision, and are commonly referred to as the wet and dry forms of AMD. In patients with advanced AMD, about two-thirds have the wet form.

5.3.1  Changes Due to Wet AMD or Choroidal Neovascularization

Wet AMD (or choroidal neovascularization) is characterized by the growth of abnormal new blood vessels underneath the retina, with a predilection for development in the foveal region (i.e. the very center of the vision, specialized and required for fine vision such as reading). These new blood vessels leak, bleed, and scar, leading to an acute drop of vision and severe visual acuity loss with progression [7]. Despite a variety of treatments (including various types of laser and photodynamic therapy), until 2005 most patients with wet AMD eventually lost vision to the 20/200 or worse level, because of recurrence of the new blood vessels. Only in this decade have there been treatments developed that address the root cause of the development of new blood vessels. Vascular endothelial growth factor (VEGF) has been identified as one of the factors stimulating new blood vessel growth. Several anti-VEGF medications have been developed. These require injection into the eye, on a monthly basis. Clinical trials using Ranibizumab (Lucentis) have shown that about 90% of patients achieve stabilization of their visual acuity, and 35% improve their visual acuity [42]. Thus, while wet AMD has been the leading cause of severe visual loss in the population over age 60, the frequency of severe visual loss from this condition should decrease markedly in the future. Patients may still be left with scotomas, with features similar to those described below.

5.3.2  Changes Due to Dry AMD or Geographic Atrophy

The second type of advanced AMD is known as the dry AMD form or geographic atrophy (GA). In this condition, there is gradual death of the retinal pigment epithelium, the layer of cells beneath the retina, with consequent death of the overlying photoreceptors and scotoma development. These areas of atrophy and scotoma may

Fig. 5.3  Progression of advanced dry age-related macular degeneration (geographic atrophy) over a 5-year period. The black outline shows the border of the atrophy and the presence of spared areas within it. (a) Baseline: there were two areas of geographic atrophy, partly surrounding the fovea. Visual acuity was 20/40. (b) One-year follow-up: the atrophy enlarged and coalesced into a horseshoe-shaped area of atrophy and corresponding dense scotoma. The fovea was spared, as was the area immediately above the fovea. Visual acuity was still 20/40, but the reading rate dropped by more than 50%. (c) Two-year follow-up: the atrophy has enlarged and the spared vertical region has gotten narrower. The fovea is still spared. Visual acuity was 20/60. (d) Threeyear follow-up: the atrophy has enlarged and coalesced superiorly, so that there is a ring of atrophy, with two small spared areas within it. Visual acuity was still 20/60. (e) Five-year follow-up: the atrophy has enlarged further, and there is only a tiny slit of fovea spared within the atrophy. Visual acuity was 20/200. The patient now used eccentric retina for reading text that was 20/600 or greater in size

first develop in areas near, but not involving, the fovea (Fig. 5.3a). As these atrophic areas enlarge and coalesce, the patient may develop a horseshoe of blind area around the fovea, and then a ring of scotoma surrounding the fovea (Fig. 5.3b) [45]. These patients may have good visual acuity, but they have difficulty reading and recognizing faces because the whole word or face does not “fit” in the spared seeing area that is surrounded by scotoma (Fig. 5.3c and 5.3d) [52]. Eventually, the fovea itself becomes atrophic and severe visual acuity loss occurs (Fig. 5.3e). Unlike wet AMD, there are no treatments available to slow or prevent vision loss in GA at the present time. Once an area becomes atrophic, the photoreceptor cells die, so that a potential treatment that prevents cell death will not restore vision to an atrophic area.

Patients with GA and other forms of advanced AMD have profound reductions in vision in dim illumination due to reduced contrast sensitivity, and require increased lighting in order to read [53]. They are also more sensitive to the effects