Coma, spherical aberration increase with age, study finds

Ocular coma and spherical aberration increase with age as a result of increased corneal coma and changes in the spherical aberration of the internal optics, according to a study. The “perfect” customized ablation will not last because of these age-related changes, the study authors said.

Shiro Amano and colleagues in Japan studied 75 eyes of 75 patients who had no history of ocular abnormalities and had a best corrected visual acuity of 20/20 or better. The patients ranged in age from 18 to 69 years.

Videokeratographic and wavefront aberration data were obtained, and measurements of a natural pupil were taken. Measurements were taken three times for each eye, and the averages of each component of the ocular and corneal higher-order aberrations in the central 6-mm area were calculated.

The spherical component of the manifest refraction for all eyes ranged from +3.5 D to –12 D. The cylinder component was –3 D or less.

Both corneal and ocular coma root mean square (RMS) showed a significant correlation with age. The study authors said the corneal and ocular comas were similar in magnitude, suggesting that the increase of ocular coma with aging is mainly a result of the increase of corneal coma.

Corneal spherical aberration did not change with age; however, there was a significant correlation between ocular spherical aberration and aging. The authors speculated that the age-dependent increase in ocular spherical aberration is probably due to changes in the lens.

“However, this hypothesis cannot yet be proven because we did not directly measure the changes of the spherical aberrations in the lens,” the authors said in the study.

Dr. Amano and his colleagues also noted a moderate individual variability. The corneal spherical aberrations were approximately 0.2 µm to 0.3 µm throughout the age range; the mean ocular spherical aberration was almost zero at 20 years of age, and it gradually increased with age.

“If an ideal customized ablation is possible, the perfect correction will not last because of the change of aberrations with age,” the authors said. “Patients undergoing wavefront-guided surgery should be informed of this.”

The study was published in the June issue of American Journal of Ophthalmology.