Simulated effect of corneal asphericity increase (Q-factor) as a refractive therapy for presbyopia.

PURPOSE: To determine the theoretical effect of an increase in the negative Q-factor (hyperprolateness) on the refractive state and its effect on presbyopia treatment.

METHODS

Ray tracing software was used to simulate the Navarro eye model. To simulate refractive therapy, corneal Q-factor ranged from 0 to -1.50. Refractive state of the model eye was defined as the target vergence required to maximize retinal image quality according to several image quality metrics. The change of refractive state produced by pupil constriction from 6 to 2 mm was estimated.

RESULTS

For 0 ≥ Q ≥ -0.6, spherical aberration of the model eye is positive, therefore, pupil miosis causes a hypermetropic shift in refractive state. Over the range -0.6 ≥ Q ≥ -1.5, spherical aberration becomes negative and pupil constriction causes the eye's far point to approach the eye, inducing a myopic shift. A maximum 0.60-diopter myopic shift in refractive state due to pupil constriction occurred for Q=-1.25.

CONCLUSIONS

Optical modeling predicts that surgically induced negative corneal Q-value will produce a change in the refractive state of the eye after pupillary miosis.