CCT emerges as data point in care

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Data from the Ocular Hypertension Treatment Study and other research show that central corneal thickness varies by race/ethnicity and predicts glaucoma risk.

By Cheryl Guttman Krader; Reviewed by James D. Brandt, MD

Sacramento, CA-Central corneal thickness (CCT) likely represents a biomarker of underlying glaucoma risk.

Results from accumulating data indicate that CCT varies by race/ethnicity and is the largest artifact affecting tonometry. While the balance between the role of CCT as tonometry artifact and biomarker in individuals and populations is not yet fully understood, current knowledge supports using information on CCT in glaucoma screening and management, according to James D. Brandt, MD.

“I would argue that we should use CCT in population screening strategies, [because] there is good evidence that CCT alone identifies high-risk individuals,” said Dr. Brandt, professor of ophthalmology and vision science and director, Glaucoma Service UC Davis Eye Center, University of California-Davis, Sacramento. “In addition, it helps to identify people at much lower risk and thereby helps avoid their over-treatment.

“In fact, in a study we reported at the 2012 meeting of the American Glaucoma Society, we showed that looking at just CCT and cup-to-disc ratio might be a very effective and efficient [strategy for] glaucoma screening,” he said.

Patient management

Regarding patient management, Dr. Brandt recommended that clinicians use the glaucoma risk calculators that incorporate CCT.

“These have been validated in multiple populations and represent the highest level of evidence-based medical practice,” he said. “Additionally, clinicians should pay attention to patients with thin corneas by obtaining good baseline data, especially disc photographs, performing increased surveillance, and shooting for a lower IOP target when appropriate.”

Dr. Brandt discussed CCT associations with race/ethnicity and how CCT might influence clinical practice as he addressed ethnic variations in glaucoma prevalence, detection, and treatment outcomes.

He noted that it was the Ocular Hypertension Treatment Study (OHTS) that brought the role of CCT in glaucoma susceptibility to the fore. OHTS data showed CCT was lower in African-American patients on average than in their Caucasian counterparts. Results of multivariate modeling of OHTS data showed that thinner CCT and a larger cup:disc ratio among patients with African-American heritage helped to explain their increased risk for developing glaucoma.

“The risk relationship with CCT was externally validated by the European Glaucoma Prevention Study, and now we believe that thinner CCT confers an almost two-fold increased risk of open-angle glaucoma,” Dr. Brandt said.

Other studies on CCT variation

Until OHTS, information on CCT variation by race/ethnicity was mostly derived from studies done in Scandinavia and Greenland. Beyond OHTS, findings from the longitudinal Barbados Eye Survey involving an Afro-Caribbean population showed that thin CCT significantly influenced glaucoma risk independent of IOP. Similarly in the Los Angeles Latino Eye Survey (LALES), CCT had a substantial impact on glaucoma risk among Hispanics that was also independent of IOP.

“Looking at the LALES cohort over time, the relationship between CCT and eventual glaucoma risk remained a powerful one,” said Dr. Brandt, referring to a recent publication in Ophthalmology.¹

Analyses of more than 30,000 data points in population-based studies that carefully characterized normal subjects and CCT also showed variations across different ethnic groups. Interestingly, Australian aboriginals had the thinnest corneas of all populations studied, but they also appear to have the lowest rate of glaucoma of any population yet studied.

“This information indicates the relationship between corneal thickness and glaucoma risk is a complex one that we still do not fully understand,” Dr. Brandt said.

As reported by Dimasi et al., who studied both humans and animals, there is also a significant relationship between skin pigmentation phenotype and CCT. Based on their findings, the investigators suggested that some of the genes controlling corneal thickness are probably closely linked to those determining pigmentation.

Reference

1. Jiang X, Varma R, Wu S, Torres M, Azen SP, Francis BA, Chopra V, Nguyen BB, Los Angeles Latino Eye Study Group. Baseline risk factors that predict the development of open-angle glaucoma in a population: the Los Angeles Latino Eye Study. Ophthalmology. 2012;119:2245-2253.

Fyi

James D. Brandt, MD

E: jdbrandt@ucdavis.edu

Dr. Brandt declares no financial interests relevant to the subject matter. The article is based on Dr. Brandt’s presentation at the 2012 annual meeting of the American Academy of Ophthalmology.