Midpoint, max-plus refraction equivalent after inlays

ANAHEIM, Calif. – Midpoint refraction is equally reliable and, on average, 0.50 D more minus when compared to a max-plus refraction in patients who have Kamra inlays, according to a poster presented at the American Academy of Optometry annual meeting.

The purpose of the study was to evaluate the reliability of midpoint refraction and how it correlates with the most commonly used max-plus manifest refraction in these patients, study author Srividhya H. Vilupuru, OD, PhD, told Primary Care Optometry News.

The prospective study of 27 subjects had the Kamra inlay for a minimum of 12 months. Subjects were randomly assigned to the observers, and each performed a max-plus manifest refraction for best corrected visual acuity and a mid-point refraction on all subjects.

“Determining the refractive endpoint in these patients can be challenging due to their ability to tolerate a wider range of refractive error without noticing a change in visual acuity,” Vilupuru told PCON.

The percentage of cases with pair-wise inter-observer agreement of spherical equivalents within ±0.25 D, ±0.50 D, and ±1.0 D were similar between max-plus manifest and midpoint refractions.

The percentage of subjects with standard deviation within 0.50 D were 89% for max-plus manifest refraction and 85% for midpoint refraction, according to researchers.

“A small percentage of Kamra inlay patients can develop a corneal wound healing response between 3 and 6 months following the implantation of the inlay,” Vilupuru said. “Early diagnosis and treatment with corticosteroids is imperative for resolution.”

The two techniques provide highly correlated measurements in small-aperture corneal inlay patients, according to the study.

“In the presence of the wound healing response, the majority of patients may exhibit a hyperopic change in refraction,” Vilupuru added. “Therefore, for the comanaging optometrist, it is important to choose either the max-plus or the midpoint technique and use it consistently to make inferences about the patient’s postoperative refractive stability and corneal health.” – by Abigail Sutton

Reference:

Vilupuru SH, et al. Reliability of refractive techniques in patients implanted with a small-aperture corneal inlay. Presented at: American Academy of Optometry annual meeting; November 9-12, 2016; Anaheim, Calif.

Disclosure: Vilupuru is manager clinical research, Ling Lin is senior manager biostatistics, clinical research, and van de Pol is a consultant to AcuFocus Inc., Irvine Calif.