Lower nasal distribution of cortical cataract: The Blue Mountains Eye Study

Previous reports have indicated that cortical cataract commences in the low er nasal lens, possibly due to sunlight exposure because of the shallow bro w temporally. The present study aimed to assess the lens sector distributio n of cortical cataract in a population. The Blue Mountains Eye Study assess ed 3654 residents aged 49-97years; 3270 phakic subjects had retroilluminati on lens photographs graded using the Wisconsin method, which divides the le ns into eight radial sectors with a grid overlay. Graders estimated percent age of cortical opacity in each sector. The lower nasal area consistently h ad the greatest opacity, a pattern present at each age and similar in both sexes, despite the 20% greater cortical cataract in women. The mean area of lens cortex involved by opacities in the lower nasal hemisphere was four f old greater than in the upper temporal hemisphere at each age. The lower na sal distribution was highly symmetrical when both eyes were affected. When > 20% of the lower nasal lens quadrant had cortical opacity, 88% of bilater ally affected subjects had cortical cataract in the same quadrant of the fe llow eye. The lower nasal distribution may indicate a role for sunlight in the aetiology of cortical cataract, which could be considered when examinin g other cortical cataract risk factors, such as diabetes, vascular disease and hormonal factors in women.