Abstract
Purpose :
This prospective study determined the efficacy of a femtosecond laser-assisted keratotomy (FLAK) nomogram (Nittany-AK calculator) for the correction of astigmatism at the time of cataract surgery.
Methods :
This study employed a novel nomogram which considered the posterior and non-keratometric contributions to total ocular astigmatism. The study included consecutive patients who underwent cataract extraction with planned FLAK and insertion of a monofocal intraocular lens by one of two surgeons. Eyes with greater than 0.5D of against the rule (ATR) or oblique astigmatism, or 1.0D of with the rule (WTR) astigmatism were treated in accordance with the nomogram. Biometry and manifest refraction were measured one month post-operatively. Target induced astigmatism (TIA) was compared to corneal and refractive surgically induced astigmatism (SIA). Outcome measures included the correction index (CI), index of success (IOS), and proportion of eyes in which the axis of astigmatism was flipped. A CI of 1.0 indicates that SIA is equal to TIA. An IOS of 0.0 indicates that there is no difference between SIA and TIA. CI and IOS were reported as geometric means for all groups.
Results :
A total of 48 eyes from 36 patients have been treated thus far, of which 21 had ATR, 19 had WTR, and 8 had oblique astigmatism. The corneal CI indicated a slight under-correction of both ATR and WTR astigmatism (ATR = 0.93, WTR = 0.86), but the refractive CI revealed an over-correction of WTR (ATR = 1.01, WTR = 1.95). Refractive IOS (ATR = 0.58, WTR = 1.01) indicated greater efficacy of the surgical intervention than the corneal IOS for all groups (ATR = 0.77, WTR = 1.11). More ATR eyes had their axis flipped based upon corneal measurements (ATR = 14.29%, WTR = 21.05%), while more WTR eyes had their axis flipped based upon refractive measurements (ATR = 9.52%, WTR = 47.37%).
Conclusions :
The Nittany-AK calculator appeared to be effective at correcting corneal astigmatism at the time of cataract surgery. Ongoing enrollment should translate to further refinements of the calculator and improvements in outcomes.
This is a 2021 ARVO Annual Meeting abstract.