Researchers in Seoul have determined that corneal power and astigmatism in eyes with keratoconus fluctuate depending on the calculation method and measurement area. The team analyzed both factors in the anterior, posterior and total cornea and found that more peripheral areas tend to exhibit a higher proportion of with-the-rim (WTR) astigmatism. Also, mean keratometry values centered on the apex were greater than those centered on the pupil when calculated using total corneal refractive powers.
The study examined the left eyes of 64 patients (41 males and 23 females with a mean age of 29.94 years) with keratoconus.
The investigators noted that some keratometric measurements obtained using a rotating Scheimpflug camera resulted in greater dioptric powers when compared with simulated keratometry values. Mean corneal powers from simulated keratometry, posterior keratometry and total net power were 49.12D, -7.39D and 47.78D, respectively.
For total corneal refractive powers centered on the pupil, mean keratometry values tended to decrease with measurement area. Both mean keratometry values and astigmatism measured using total corneal refractive powers centered on the apex decreased with measurement area. The proportion of WTR astigmatism was greatest on the anterior and total cornea. As the measurement area moved to the periphery, the proportion of WTR astigmatism increased.
“We believe these findings will help to enhance our understanding of the anatomical and optical characteristics of keratoconus as well as our ability to diagnose keratoconus and determine IOL power in the future,” the study authors concluded in their paper.
Kim J, Whang WJ, Kim HS. Analysis of total corneal astigmatism with a rotating Scheimpflug camera in keratoconus. Br J Ophthalmol. December 3, 2020. [Epub ahead of print].