Higher-order aberrations from the internal optics of the eye.

PURPOSE: To analyze the distribution of human higher-order wavefront aberrations (3rd- to 6th-order) from the internal optics (WA(internal)) and the variations with age and to evaluate the degree of compensation that the internal optics provide for anterior corneal aberrations (WA(cornea)). SETTING: Cullen Eye Institute, Baylor College of Medicine, Houston, Texas, USA. METHODS: With assumption of a simple model for the eye, the WA(internal) were obtained by direct subtraction of the WA(cornea) from the ocular aberrations (WA(eye)). The WA(eye) were measured using the WaveScan system (Visx, Inc.), and the WA(cornea) were computed from the topographic data (Humphrey Atlas) using the CTView program (Sarver and Associates, Inc.). In 144 eyes of 114 normal patients (age 20 to 69 years), WA(internal) were calculated for a 6.0 mm pupil and a compensation factor (CF) was computed, with positive values representing compensation of WA(cornea) by WA(internal) and negative values indicating that the internal surfaces add aberrations to those of the cornea. RESULTS: There was wide individual variation in WA(internal). The mean coefficient for 4th-order spherical aberration (Z(4)(0)) was -0.145 microm +/-0.094 (SD) (95% confidence interval [CI], -0.160 to -0.130 microm); 95.1% of eyes had negative values. The mean root-mean-square value for HOAs was 0.334 +/- 0.096 microm (95% CI, 0.319 to 0.350 microm). Moderate to high correlations were found between the right and left eyes in HOAs, 4th-order and 6th-order spherical aberration coefficients (Z(4)(0) and Z(6)(0)). With increasing age, the HOAs did not change, whereas the negative coefficients for Z(4)(0) tended to become less negative. Only the term Z(4)(0) had a CF significantly correlated with increasing age (r=-0.338, P<.05 with Bonferroni correction). CONCLUSION: WA(internal) varied widely among patients, and a moderate to high degree of mirror symmetry existed between the right and left eyes. Internal surfaces compensated at least partially for the HOA and Z(4)(0) in most eyes, and this compensation decreased only mildly with increasing age.

Comparison of intraocular lens power calculation methods in eyes that have undergone LASIK.

OBJECTIVE: To compare methods of calculating intraocular lens (IOL) power for cataract surgery in eyes that have undergone myopic LASIK. DESIGN: Noncomparative case series. PARTICIPANTS: Eleven eyes of 8 patients who had previously undergone myopic LASIK (amount of LASIK correction [+/-standard deviation], -5.50+/-2.61 diopters [D]; range, -8.78 to -2.38 D) and subsequently phacoemulsification with implantation of the SA60AT IOLs (Alcon Surgical, Inc., Fort Worth, TX) were included (refractive error after cataract surgery, -0.61 +/- 0.79 D; range, -2.0 to 1.0 D). METHODS: We evaluated the accuracy of various combinations of: (1) single-K versus double-K (in which pre-LASIK keratometry is used to estimate effective lens position) versions of the IOL formulas; the Feiz-Mannis method was also evaluated; (2) 4 methods for calculating corneal refractive power (clinical history, contact lens overrefraction, adjusted effective refractive power [EffRP(adj)], and Maloney methods); and (3) 4 IOL formulas (SRK/T, Hoffer Q, Holladay 1, and Holladay 2). The IOL prediction error was obtained by subtracting the IOL power calculated using various methods from the power of the implanted IOL, and the F test for variances was performed to assess the consistency of the prediction performance by different methods. MAIN OUTCOME MEASURES: Mean arithmetic IOL prediction error, mean absolute IOL prediction error, and variance of the IOL prediction error. RESULTS: Compared with double-K formulas, single-K formulas predicted lower IOL powers than the power implanted and would have left patients hyperopic in most cases; the Feiz-Mannis method had the largest variance. For the Hoffer Q and Holladay 1 formulas, the variances for EffRP(adj) were significantly smaller than those for the clinical history method (0.43 D2 vs. 1.74 D2, P = 0.018 for Hoffer Q; 0.75 D2 vs. 2.35 D2, P = 0.043 for Holladay 1). The Maloney method consistently underestimated the IOL power but had significantly smaller variances (0.19-0.55 D2) than those for the clinical history method (1.09-2.35 D2; P<0.015). There were no significant differences among the variances for the 4 formulas when using each corneal power calculation method. CONCLUSIONS: The most accurate method was the combination of a double-K formula and corneal values derived from EffRP(adj). The variances in IOL prediction error were smaller with the Maloney and EffRP(adj) methods, and we propose a modified Maloney method and second method using Humphrey data for further evaluation.

Comparison of intraocular lens power calculation methods in eyes that have undergone laser-assisted in-situ keratomileusis.

PURPOSE: To compare methods of calculating intraocular lens (IOL) power for cataract surgery in eyes that have undergone myopic laser-assisted in-situ keratomileusis (LASIK). METHODS: Eleven eyes of eight patients who had previously undergone myopic LASIK (amount of LASIK correction, -5.50 +/- 2.61 D (SD); range, -8.78 to -2.38 D) and subsequently phacoemulsification with implantation of the SA60AT IOLs were included (refractive error after cataract surgery, -0.61 +/- 0.79 D; range, -2.0 to 1.0 D). We evaluated the accuracy of various combinations of (1) single-K versus double-K (in which pre-LASIK keratometry is used to estimate effective lens position) versions of the IOL formulas; the Feiz-Mannis method was also evaluated; (2) four methods for calculating corneal refractive power (clinical history, contact lens overrefraction, adjusted EffRP (EffRP(adj)), and Maloney methods); and (3) four IOL formulas (SRK/T, Hoffer Q, Holladay 1, and Holladay 2). The IOL prediction error was obtained by subtracting the IOL power calculated using various methods from the power of the implanted IOL, and the F test for variances was performed to assess the consistency of the prediction performance by different methods. RESULTS: Compared to double-K formulas, single-K formulas predicted lower IOL powers than the power implanted and would have left patients hyperopic in the majority of the cases; the Feiz-Mannis method had the largest variance. For the Hoffer Q and Holladay 1 formulas, the variances for EffRP(adj) were significantly smaller than those for the clinical history method (0.43 D2 vs 1.74 D2, P = .018 for Hoffer Q; 0.75 D2 vs 2.35 D2, P = .043 for Holladay 1). The Maloney method consistently underestimated the IOL power but had significantly smaller variances (0.19 to 0.55 D2) than those for the clinical history method (1.09 to 2.35 D2) (P < .015). There were no significant differences among the variances for the four formulas when using each corneal power calculation method. CONCLUSIONS: The most accurate method was the combination of a double-K formula and corneal values derived from EffRP(adj). The variances in IOL prediction error were smaller with the Maloney and EffRP(adj) methods, and we propose a modified Maloney method and second method using Humphrey data for further evaluation.

Late laser in situ keratomileusis flap dislocation caused by a thrown football.

A 38-year-old man sustained a dislocated flap after being struck in the left eye with a football more than 30 months after uneventful laser in situ keratomileusis (LASIK). Consequent epithelial ingrowth and microstriae required surgical treatment. The postoperative course was uneventful with recovery of 20/20 Snellen uncorrected visual acuity. This case illustrates the need for LASIK patients to wear protective eyewear when participating in contact sports.

Comparison of two grading methods to evaluate focal narrowing of retinal arterioles in glaucoma.

BACKGROUND: Focal arteriolar narrowing has been reported to be more common in glaucoma eyes compared to normal eyes. The current study was performed to compare two methods for standardized assessment of focal arteriolar narrowing. MATERIAL AND METHODS: Stereoscopic optic disc photographs (from one randomly selected eye per subject) of 48 normal subjects, 20 ocular hypertensive patients (OHT), and 29 glaucoma patients, were reviewed independently in a masked fashion by two graders. Focal arteriolar narrowing within one disc diameter from the rim edge was evaluated based on two different grading methods: (1) narrowing present if the arteriole was wider distal to the narrowing, and (2) narrowing present if the arteriole was wider both distal and proximal to the narrowing. RESULTS: Focal arteriolar narrowing was observed with grading method 1 in 37.5% (18/48), 35.0% (7/20), and 65.5% (19/29) of normals, OHT, and glaucoma patients, respectively. It was observed with grading method 2 in 18.8% (9/48), 0% (0/22), and 48.3% (14/29) of normals, OHT, and glaucoma patients, respectively. With both grading methods, focal arteriolar narrowing was significantly more frequent in glaucoma versus normal eyes (chi-square test: grading method 1 P=0.03, and grading method 2 P=0.0001). The number of eyes with focal arteriolar narrowing was significantly more frequent with method 1 than with method 2 across all photographs and all subgroups (chi-square test: P=0.0001). The overall agreement between the two graders was kappa 0.77+/-0.06 for grading method 1, and 0.43+/-0.11 for grading method 2. CONCLUSIONS: The prevalence of focal arteriolar narrowing is highly dependent upon the grading method. A uniform grading method of focal arterial narrowing is needed to achieve comparable and reproducible results among studies.