Researchers based at the Centre for Vision Research, Westmead Institute, University of Sydney, have reported their findings using three population-based cohorts to show the proportion of patients progressing from unilateral AMD to bilateral involvement. The Three Continent AMD Consortium (3CC) investigated progression of the disease in relation to risk factors and early AMD lesion characteristics. The study found that between one in four and one in five unilateral “any AMD cases”, and up to one in two unilateral “late AMD cases”, progressed to bilateral in 5 years.  The authors concluded that several AMD risk factors, including smoking, appear to be significantly associated with the progression to bilateral involvement.

Clearly, AMD in one eye can be significantly debilitating however, vision loss and blindness in both eyes carries severe consequences and, as such, accurate prognoses on progression to bilateral AMD are critical to improving clinical care and management.   Previous studies on similar patient populations had reported the development of late AMD in the bilateral eye to be 20–50% over 5–10 years however, less well described has been the progression from unilateral early AMD to bilateral early or any (early and late) AMD, and the progression of same in the context of risk factors. To assess this question in more detail the researchers pooled data analyses of three prospective population-based cohorts: the Blue Mountains Eye Study, the Beaver Dam Eye Study and the Rotterdam Study.

In performing the study the researchers analyzed retinal images and conducted interviews with comprehensive questionnaires and found that in any 5-year duration, 19–28% of unilateral any AMD cases developed into bilateral disease, while 27–68% of unilateral late AMD became bilateral. Several factors were recorded in association with the progression to bilateral disease including age (per year increase, adjusted OR 1.07), carrying risk alleles of the complement factor H (CFH) and age-related maculopathy susceptibility 2 genes (compared with none, OR 1.76 for 1 risk allele and OR 3.34 for 2+ risk alleles). In addition, smoking and the presence of large drusen area or retinal pigmentary abnormalities in the first eye, also associated with disease progression. In respect of smolking, when compared with non-smokers, there was an OR for progression of 1.64 for past and an OR of 1.67 for current smokers, leading the researchers to comment that, “of risk factors associated with the progression to bilateral involvement, only smoking is modifiable.”