City Research Online

Abstract

Macular pigment (MP) at the centre of the retina is thought to serve a protective function shielding the photoreceptors from damaging effects of blue light. The amount of MP and its spatial density distribution across the macula i.e. its spatial profile varies among individuals. Lower levels of MP and certain MP spatial profile phenotypes are believed to be associated with increased risk of age-related macular degeneration (AMD). There is suggestion that MP spatial profiles differ between ethnicities, with non-exponential profiles occurring more frequently in non-whites. This may explain some of the ethnic variations seen in AMD prevalence. However, previous investigations have used several methodologies to measure MP. In addition, inconsistent MP spatial profile definitions have been used; thus comparing data between studies is difficult. Nevertheless, it has been hypothesised that variations in MP spatial distribution could be due to differences in foveal architecture, in particular at the foveal centre where MP levels peak.

A study was designed to investigate the effect of ethnicity on MP spatial density distribution and its relation to foveal architecture. The influence of known risk factors for AMD was also considered. Young (18 to 39 years), healthy volunteers of white (n = 76), South Asian (n = 80) and black (n = 70) ethnic origin were recruited to take part. MP measurements were obtained using a method based on heterochromatic flicker photometry (HFP) and foveal morphology measurements were taken from optical coherence tomography (OCT) scans. The coefficients of repeatability of each of these were confirmed in a sub-study. A systematic objective MP spatial profile classification technique was implemented throughout. The feasibility of applying this to MP measurements obtained with different techniques such as HFP and fundus autofluorescence (FAF) was also explored in a sub-study.

The results showed that measures of MP optical density (MPOD) over the central retinal area were statistically significantly increased in South Asian and black compared to white subjects, whereby ethnicity explained around 10% of the variation (P < 0.0005). Non-exponential MP spatial profiles (ring-like and central dip respectively) were significantly more prevalent in South Asian and black compared with white subjects (χ2 (4, n = 226) = 13.4, P = 0.009). Integrated MPOD up to 1.8º was significantly increased in ring-like and central dip compared to exponential profiles (P < 0.0005) irrespective of ethnicity. South Asian and black individuals presented thinner central retinas and wider foveas compared to white individuals (P < 0.0005). However, while accounting for these ethnic variations, foveal architecture provided no predictive values for the MP spatial profile phenotype.

Publication Type:	Thesis (Doctoral)
Subjects:	R Medicine > RE Ophthalmology
Departments:	Doctoral Theses School of Health & Psychological Sciences > Optometry & Visual Sciences School of Health & Psychological Sciences > School of Health & Psychological Sciences Doctoral Theses

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