Corneal sensitivity influenced by iris pigmentation

FORT LAUDERDALE, Fla. — As iris pigmentation increases, corneal sensitivity decreases, according to the results of a study.

Anna M. Ntola and colleagues set out to assess the effect of iris pigmentation and ethnicity on corneal sensitivity, skin sensitivity, tear film breakup time and blink rate. They presented their results in a poster here at the Association for Research in Vision and Ophthalmology meeting.

For the study, 200 subjects were divided into four ethnic groups: white (100 patients), Asian (40 patients), Chinese (40 patients) and African (20 patients). Patients were classified according to iris color. Researchers said all measurements were made on the right eye only, and they were made after 12 p.m. “to avoid any diurnal bias.”

The authors said that skin sensitivity was assessed at the upper closed eyelid; tear film breakup time was assessed following the instillation of 0.7 µL of fluorescein; and blink rate was video recorded for 5 minutes and digitally analyzed.

The researchers concluded that corneal sensitivity is affected by iris color and ethnicity and that whites have a progressive decrease in sensitivity with increasing iris pigmentation.

They added that “tear film stability is not affected by iris color, although a significant difference was found between measurements.” The researchers suggested that dark-brown eyes tended to maintain a more stable tear film. Additionally, they said, tear film stability “is not affected by ethnic group.”

Finally, no significant difference was found in blink rate between the different iris color grades or ethnic groups. The authors said that only a “weak relationship” was found between corneal sensitivity and blink rate for all patients studied; however, patients with lower-than-average corneal sensitivity blinked more often than subjects with higher-than-average corneal sensitivity. They also found that blink rate decreased as corneal sensitivity decreased.