A Smartphone Application to Predict Post-DSAEK Refractive Shift

Abstract

Purpose: To develop a web and smartphone application that predicts refractive shift after Descemet stripping automated endothelial keratoplasty.

Methods: An application to estimate post-DSAEK refractive shift was written for iPhone, Android, and web use based on a mathematical model that we have developed (Hwang RY, Gauthier DJ Wallace D, Afshari NA. IOVS 2011). Our model used the patient’s preoperative central corneal thickness and posterior radius of curvature along with the graft’s central thickness and central to peripheral ratio to estimate post-DSAEK refractive shift. Posterior corneal power after DSAEK was derived from the patient’s pre-DSAEK corneal posterior radius of curvature (r_pc); the graft's central thickness (t_transplant), central to peripheral ratio (CP), and center to periphery distance (h'); and the refractive indices for aqueous humor and cornea (n₃ and n₂). F_pc+DSAEK=(n₃-n₂)/r_pc''=(n₃-n₂)(1/(r_pc-t_transplant)+(2*t_transplant(1/CP-1))/h'²) Total corneal power was then calculated from anterior corneal power (F_ac), posterior corneal power (F_cornea+DSAEK), and the refractive power of the corneal thickness itself. t is the patient’s pre-DSAEK central corneal thickness. F_cornea+DSAEK=F_ac+F_pc+DSAEK-(t+t_transplant)(F_ac)(F_pc+DSAEK)/n₂ Next, total ocular power was obtained from total corneal power (F_cornea+DSAEK), lens power (F_lens), and other refractive parameters. d is the distance between the principal planes of the cornea and the lens. F_eye+DSAEK=F_cornea+DSAEK+F_lens-d/n₃(F_cornea+DSAEK)(F_lens) The refractive shift was finally calculated as the difference between total eye power with DSAEK and total eye power without DSAEK (t_transplant=0 and CP=1).

Results: An application for easy calculation of post-DSAEK refractive shift was developed for iPhone, Android, and web use. The application was tested retrospectively to compare predicted post-DSAEK refractive shifts against actual post-DSAEK refractive shifts measured in four patients. The average measured refractive shift was 0.89D (0.75D-1.0D) and the average predicted refractive shift was 0.83D (0.75D-0.88D) or 93% of the average measured refractive change.

Conclusions: We have developed an application for iPhone, Android, and web use that estimates refractive shift after Descemet stripping automated endothelial keratoplasty. Our application can aid in IOL selection during DSAEK surgery. To our knowledge this is the first smartphone application for corneal surgery.

Keywords: 741 transplantation • 567 intraocular lens • 445 cataract