Intraocular lens calculations after hyperopic refractive surgery.
OBJECTIVE
To evaluate the effect of hyperopic refractive surgery on intraocular lens (IOL) power calculation, compare published methods of IOL power calculation after refractive surgery, evaluate the effect of prerefractive surgery refractive error on IOL deviation, and introduce a new alternative formula for IOL calculation in patients who have had refractive surgery for hyperopia.


METHODS
Retrospective noncomparative case series.


METHODS
Twenty eyes from 13 patients who had undergone cataract surgery after previous hyperopic refractive surgery.


METHODS
Seven different methods of IOL calculation were performed retrospectively: clinical history (IOL(hisK)), clinical history method at spectacle plane (IOL(hisKs)), vertex (IOL(vertex)), back calculated (IOL(BC)), calculation based on average keratometry (IOL(avgK)), calculation based on steepest keratometry (IOL(steepK)), and calculation based on the double K formula (IOL(doubleK)). Each method's result was compared with an exact IOL (IOL(exact)), which would have resulted in emmetropia. Each method was then compared with change in spherical equivalent induced by refractive surgery (SE(h)). A paired t test was used to determine statistical significance.


METHODS
Mean error in IOL power prediction for each method when compared to IOL(exact).


RESULTS
When evaluating different methods of IOL calculations, IOL(vertex) was the most accurate, with a mean deviation from emmetropia of 0.42+/-1.75 diopters (D), followed by IOL(BC) (+0.54+/-1.86 D), IOL(hisK) (+1.56+/-2.35 D), IOL(hisKs) (+1.57+/-2.35 D), IOL(steepK) (+1.59+/-2.25 D), IOL(doubleK) (+1.65+/-2.56 D), and IOL(avgK) (+2.24+/-2.46 D). There was no statistical difference between IOL(vertex), IOL(BC), and IOL(exact). The power of IOL(avgK) would be inaccurate by 0.27x+1.53, where x = SE(h). Thus, most patients without the adjustment to IOL(avgK) would be left myopic. However, when IOL(avgK) is adjusted with this formula, there is no statistical difference to IOL(exact).


CONCLUSIONS
For IOL power selection in previously hyperopic patients, a predictive formula based only on SE(h) and current average keratometry readings was not found to statistically differ from IOL(exact). The IOL(vertex) and IOL(BC), which also did not statistically differ from IOL(exact), require prerefractive surgery keratometry readings that are often not available to the cataract surgeon.
Chokshi
Amit R
AR
Department of Ophthalmology, University of Florida, Jacksonville, Florida, USA.
Latkany
Robert A
RA
Speaker
Mark G
MG
Yu
Guopei
G
D000465:Algorithms; D001699:Biometry; D002386:Cataract / Q000150:complications; D006801:Humans; D006956:Hyperopia / Q000503:physiopathology / Q000601:surgery*; D020731:Keratomileusis, Laser In Situ; D019654:Lens Implantation, Intraocular; D007910:Lenses, Intraocular; D018918:Phacoemulsification; D012029:Refraction, Ocular / Q000502:physiology; D012189:Retrospective Studies