“How soon will my good eye go bad?”

This is commonly-asked by people affected with unilateral age-related macular degeneration (AMD). AMD is a chronic and progressive disease, and the chances are good that it will eventually affect both eyes. The question about when that will happen has been addressed by a three-continent study published in January 2017 by the British Journal of Ophthalmology.
Researchers analyzed data from participants in three past studies: the Blue Mountains Eye Study, the Beaver Dam Eye Study and the Rotterdam Study. Subjects with unilateral AMD were examined and interviewed over five years, and each individual’s risk factors were also taken into account. This included age, genetic risk, history of smoking, and presence of large drusen or retinal abnormalities in the first eye.
The researchers found that after five years, 19-28% of  cases with all stages of AMD became bilateral, and 27-68% of those specifically with late AMD (geographic atrophy or neovascularization) became bilateral. In other words, about one in four (25%) people with any stage of AMD in one eye can expect it to progress to both eyes within about five years. If, however, a person has late AMD in one eye, the chance increases to one in two (50%).
In addition to identifying the time element, this study has reconfirmed the known risk factors significantly associated with progression to both eyes, with tobacco smoking being the only risk that can currently be eliminated or reduced.
Five-year progression of unilateral age-related macular degeneration to bilateral involvement: the Three Continent AMD Consortium report. Nichole Joachim et al (Br J Ophthalmol, doi:10.1136/bjophthalmol-2016-309729