Comparison of contact lens overrefraction and standard keratometry for measuring corneal curvature in eyes with lenticular opacity.
OBJECTIVE
To assess the accuracy of corneal power measurement by contact lens overrefraction in patients with normal corneas and to determine the suitability of this method for use in intraocular lens (IOL) calculations.


METHODS
General ophthalmology clinic at a public hospital (Ben Taub General Hospital, Houston, Texas, USA).


METHODS
Using contact lens overrefraction (CLO), and standard keratometry, the corneal power in 33 eyes of 20 normal patients and patients scheduled for cataract extraction was prospectively measured. The eyes were divided into 3 groups based on their best spectacle-corrected visual acuity: (1) 20/20 to 20/40, (2) 20/50 to 20/70, and (3) 20/80 to 20/400. For each group, the means (absolute and arithmetic), standard deviations, and ranges of differences in corneal power as measured by CLO and keratometry were calculated. These values were used to estimate the induced variance in refractive outcome for IOL calculations.


RESULTS
The mean absolute differences in corneal power by group were 0.35 diopter (D) +/- 0.18 (SD), 0.54 +/- 0.33 D, and 0.77 +/- 0.28 D, respectively. The mean arithmetic differences in corneal power were -0.05 +/- 0.39 D, +0.37 +/- 0.51 D, and +0.17 +/- 0.80 D, respectively.


CONCLUSIONS
In eyes of patients with good visual acuity (20/20 to 20/40), corneal power measurements by CLO and keratometry were similar. The accuracy of the CLO-derived value decreased with increasing media opacity but was still acceptable with acuity of 20/70. Contact lens overrefraction may be a viable alternative to refractive history and videokeratography for estimating true corneal power in patients with surgically altered or irregular corneas.
Zeh
W G
WG
Cullen Eye Institute, Baylor College of Medicine, Houston, Texas, USA.
Koch
D D
DD
D002386:Cataract / Q000150:complications*; D003261:Contact Lenses; D003315:Cornea / Q000473:pathology*; D003941:Diagnostic Techniques, Ophthalmological; D005500:Follow-Up Studies; D006801:Humans; D011446:Prospective Studies; D012029:Refraction, Ocular; D012030:Refractive Errors / Q000175:diagnosis*; D015203:Reproducibility of Results; D014792:Visual Acuity