My 60-year-old white patient has a large, raised lesion in the posterior pole. It is mostly nonpigmented, with a small area on the nasal border that is grey. I didn’t see any vascular abnormality on or near it, and there weren’t drusen overlying it. I don’t have a camera and want to accurately document the lesion in the clinical records. How can I accurately note it’s size and location in millimetres?

Because one of the most critical aspects in describing any posterior segment lesion is its size, it’s useful to remember that the diameter of the optic disc is just about 1.5 mm, on average. I have become accustomed to estimating the size of retinal findings in disc diameters (DD), but it’s more clinically accurate to estimate, or, better yet, measure and record the size of suspicious areas in millimetres, in at least two dimensions.

The disc is a handy estimation tool, but it’s not a precisely accurate ‘ruler’ for measuring lesion size. For example, a pigmented lesion that’s roughly 1DD long by roughly 2DD wide would be better recorded as ‘approximately 1.5mm vertical x 3mm horizontal.’ This will help in monitoring retinal pigmented lesions and enable earlier detection of any change in size. A change in size can indicate a change from benign to malignant. If all the practitioners in the practice adopt this system a change in size is less likely to be missed if the patient is examined by different clinicians.