We chose cases with only the late forms of AMD—namely, GA and CNV with photographic grading confirmation. Smoking is a well established risk factor for AMD and therefore a potential confounder in studies such as this. From a detailed analysis of smoking parameters, which we report elsewhere, we have shown that pack years of smoking cigarettes is the measure most strongly associated with risk of AMD and we incorporated this in our logistic regression model. We used a validated iris grading method and the kappa statistic for agreement between different observers was high, comparable with the value of 0.76 reported by Seddon et al
We were unable to demonstrate an association of AMD with iris colour or a change in iris colour. This is in agreement with the larger case‐control studies and population studies that found no association between iris colour and AMD.3,6,7,11,12,13,14,15
Three case‐control studies have demonstrated an association between light iris colour and macular degeneration.16,17,18
Unlike the present investigation, these studies looked at cases with a broad definition of macular degeneration, which included cases of ARM as well as AMD. The control groups are not clearly defined in two of the studies.17,18
Holz et al19
demonstrated that although light iris colour appeared to be a risk factor for ARM, there was no increased risk when considering the patients' own perception of their eye colour at age 20 and from this the authors surmised that the increased risk was actually associated with a lightening in iris colour. In the Blue Mountains Eye Study4
an association was detected for blue iris colour alone when compared with all other iris colours in late AMD using multiple logistic regression adjusting for smoking, age, and sex. In this study, combining all other iris grades and comparing with blue we were unable to detect any such association (data not shown).
No differences in reported hair colour at age 20 were found between cases and controls; this is consistent with the findings of Mitchell et al
in the Blue Mountains Eye Study.4
In a case‐control study, Darzins et al1
reported significantly poorer tanning ability (skin types I or II) in cases with AMD using a univariate analysis. Using the same method of analysis we too were able to demonstrate this association (χ2
4.4, df 1, p
0.04, data not shown), but this ignores possible confounding factors.
This study shows a possible association between poorer tanning ability and GA but with borderline significance in the context of several risk factors being tested. Data from the Blue Mountains Eye Study4
indicated increased risk of AMD in those with both greater skin sun sensitivity and in those with reduced skin sun sensitivity; possibly explained by increased biological risk in those with sensitive skin but increased sun exposure in the darker skin category.
We were unable to demonstrate a link between estimated lifetime sun exposure and late AMD and this result is consistent with the findings from other studies.1,2,3
Data from the Beaver Dam Eye Study demonstrated an association with early ARM in men but no association with AMD.2
Estimates of sun exposure are notoriously difficult to make. Some authors have used detailed questionnaires to calculate average yearly sunlight hours and combined this with measurements of ambient ultraviolet B.20
We were unable to achieve this level of detail because, in contrast with these population studies, the participants in this study were elderly and unable to recall such information with accuracy. Since our estimates of sun exposure were necessarily crude we assessed the incidence of skin cancers as a proxy measure of sun exposure but this also showed no association with AMD.