Corneal anthropology: Ethnicity-based central corneal thickness measurements in managing corneal disorders

Dear Editor, Ethnicity is known to affect the ocular and periocular measurements.1 Central corneal thickness (CCT) is the most heritable trait in the human body.2 Genome-wide association analysis in multiethnic Asian groups has shown genes that affect CCT and its variation between ethnic groups.3 The difference in baseline CCT suggests that ethnicity may affect the prevalence and severity of certain corneal disorders. Asian ethnic groups have a fourfold more incidence of keratoconus and these patients present at a younger age and progress faster as compared to the Whites.4 Therefore, the treatment options for keratoconus may be customized on the basis of the ethnic origin of the individual. Population groups of African origin have been reported to have thinner corneas compared to the whites.5 Apart from African Americans, the Japanese have been reported to have thinner corneas compared to other ethnicities.6 CCT has been shown to be the strongest predictive factor for glaucoma progression, independent of intraocular pressure (IOP).7 Pachymetry-adjusted IOP values play a significant role in glaucoma management.8 In the Chennai Glaucoma study from South India, the urban group had a mean CCT of 520.7 ± 33.4 μm and significantly lower in the rural group with glaucoma (505.9 ± 31.1 mm).9 Another study from a nearby urban region (Bangalore, Karnataka) found similar CCT values and significantly lower than the internationally accepted CCT value (545 mm).10 The authors suggested the use of local ethnic group CCT to ascertain the pachymetry-corrected IOP. Patient selection for refractive laser eye surgery and choice of surgical procedure (photorefractive keratectomy, laser in-situ keratomileusis, small incision lenticule extraction) should also be based on local ethnic CCT rather than the international accepted value.11 Endothelial cell density (ECD) has also been seen to vary between various groups. In a study, the Iranian population had lower ECD as compared to Indian and American groups.12 According to the authors, this may have a role to play in the lower incidence of pseudophakic bullous keratopathy in groups like the Japanese, who have higher ECD values.13 Ethnicity-based clinical, genetic, and molecular research is still in infancy. Research on genes responsible for normal CCT variation is being done by candidate gene approach, familial linkage analysis, and genome-wide association studies.2 It has a great potential in the diagnosis, monitoring, and optimizing treatment options for corneal disorders. The term “corneal anthropology” should be used for ethnicity-based corneal research. Financial support and sponsorship Nil. Conflicts of interest There are no conflicts of interest.