Optometrists have become well versed in the presentations of age-related macular degeneration (AMD), given its prevalence. Once that's been firmly entrenched in your clinical skillset, to take it to the next level you'll want to make sure that you're inclusive of the non-AMD macular problems that present in your practice. By doing so, you'll be able to isolate and differentially diagnose these conditions to better counsel and manage your patients.
The list of AMD masqueraders is lengthy and variable, including conditions that are degenerative, infectious, inflammatory, toxic, vascular, traumatic, neoplastic and paraneoplastic. Any condition that affects the retinal pigment epithelium (RPE) and outer retina may lead to drusenoid or lipofuscin deposition and/or pigmentary alteration that can mimic AMD. (1) In this article, we will focus only on the non-AMD dystrophies and degenerations that affect the macula--a list that is already quite diverse and extensive.
What Stresses the Macula?
As it turns out, the lifelong responsibility of converting light energy into electrical potential to initiate the process of sight is a very stressful job. The photoreceptors, RPE and choroid must constantly work in sync to maintain the visual cycle, regenerate photoreceptor outer segments and remove and phagocytize metabolic waste products. Environmental factors such as UV light exposure and tobacco smoke put strain on this delicate balance, as do systemic conditions such as vascular disease. In addition, numerous faulty pathways can disrupt this system through various mechanisms. (2,3)
Phenotypical outcomes of various stressors can present similarly. Different pathways of damage may lead to clinically similar presentations that are difficult to distinguish from each other. Diagnostic imaging such as optical coherence tomography (OCT), fundus autofluorescence (FAF), fluorescein angiography (FA) and OCT angiography (OCT-A) alongside evaluation of retinal function with tools such as electrodiagnostics may help to narrow down a diagnosis. Additional factors such as age of onset, presenting symptoms and family history are also important, as these vary among different conditions.
The most commonly encountered inherited macular dystrophy, Stargardt's, affects one in 8,000 to 10,000 individuals. (4) Stargardt's disease is most commonly inherited in an autosomal recessive fashion primarily by disease-causing variants of the ABCA4 gene.
This condition typically presents between the ages of 10 and 20, with a resultant visual acuity around 20/200. (5,6) Presentation later in life usually results in better visual acuity outcomes. Patients often present with classic pisiform-shaped, yellow lesions or fleck-like lesions as well as macular atrophy with a "beaten bronze" appearance (Figure 1). (6) Presentation of pisiform lesions without evidence of macular atrophy was initially termed fundus flavimaculatus, but is now recognized as a phenotypic variant of Stargardt's disease. (7)
Diagnostic imaging is very useful in identifying and differentiating patients with Stargardt's. Presentation is often subtle at first with visual symptoms being more severe than clinical signs. (8) Care must be taken to identify these patients as to not misdiagnose them or perform unnecessary testing or procedures. OCT may show early thicken ing of the external limiting membrane. FAF may uncover early alterations and lipofuscin...