On-eye spherical aberration of soft contact lenses and effective lens power

Purpose:  Soft contact lenses (SCL) produce a significant level of spherical aberration (SA). A simple model assuming that a thin SCL aligns to the cornea predicts that these effects are similar on-eye and off-eye. We investigate the effect SA has on the power of an SCL on-eye.
Methods:  The wavefront aberration for 17 eyes and 33 SCL on-eye was measured with a Shack–Hartmann wavefront sensor. The Zernike coefficients describing the on-eye SA of the SCL were compared with off-eye ray tracing results. Paraxial and effective lens power changes resulting from the SCL-induced SA were determined.
Results:  The model predicts the on-eye SA of SCL closely. The SA induced by spherical SCL partly cancelled the ocular SA for 11 of the subjects. The power change resulting from SCL-induced SA is ±0.5 D for a ±7.00 D spherical SCL on a 6-mm pupil. Power change is negligible for SCL corrected for off-eye SA.
Conclusions:  For thin SCL the level of SA is similar on-eye and off-eye. SCL corrected for off-eye SA are aberration free on-eye but the benefit depends on the individual level of ocular aberrations and the viewing condition. The effective power change of spherical SCL depends on pupil size and can be significant for large pupils even for moderate refractive errors. For SCL without aberration correction, for higher levels of ametropia and large pupils, the SCL power should be determined with trial SCL with their power and p -value similar to the prescribed lens.     

Soft contact lens-induced longitudinal spherical aberration and its effect on contrast sensitivity

Some investigators have suggested that the poor quality of vision which some spherical, single vision, soft lens-wearing patients report may be a result of spherical aberration induced in the ocular system when a soft lens is placed on the eye. In this study, the longitudinal spherical aberration of spherical soft lenses, both on and off the eye, was calculated using an aspheric corneal model and two-dimensional ray tracing program. Specifically designed front-surface aspheric, soft lenses were produced which demonstrated levels of in-air power variation similar to that calculated for similar-parameter spherically surface lenses. The effect of these lenses on the visual performance of nine subjects was assessed by measuring changes in contrast sensitivity and high contrast visual acuity through 3- and 6-mm artificial pupils. Significant losses of contrast sensitivity were recorded for the spherically aberrated lenses with the 6-mm pupil but not with the 3-mm pupil. High contrast acuity was not affected by any of the aberrated lenses with either the 3- or 6-mm pupils. Theoretical calculations and the contrast sensitivity results indicate that negatively powered lenses produce significantly less spherical aberration in situ than positively powered lenses. Because the majority of the prepresbyopic soft lens-wearing population have low to moderate amounts of myopia, it would appear that soft lens-induced spherical aberration is unlikely to be responsible for the reduction in visual performance which some patients report when corrected with single vision soft lenses.     

On-eye performance of custom wavefront-guided soft contact lenses in a habitual soft lens-wearing keratoconic patient

PURPOSE: To assess visual, optical, and fitting characteristics for wavefront-guided soft contact lenses produced for one habitual soft lens-wearing moderate keratoconic eye. METHODS: A process for production and evaluation of custom wavefront-guided soft contact lenses was developed. Wavefront aberrations were quantified with the COAS-HD wavefront sensor (Wavefront Sciences); soft contact lenses containing both high and low order aberrations were designed with custom software and produced using an ophthalmic lens lathe. Photopic high and low contrast logMAR visual acuity were recorded with the lens in place over an artificial 5-mm pupil and residual 2nd to 10th order root-mean-square (RMS) aberrations were analyzed over a 5-mm pupil. Comparisons were made to the eye's habitual toric soft contact lens using t tests. RESULTS: Photopic high contrast values for habitual and final custom contact lenses for a 5-mm pupil were 0.07+/-0.06 and -0.08+/-0.05, respectively. Photopic low contrast values were 0.73+/-0.06 and 0.62+/-0.07, respectively. Habitual and final custom correction low order RMS over a 5-mm pupil were 2.08 and 0.34 microm, and high order RMS levels were 0.77 and 0.39 microm, respectively. CONCLUSIONS: The final custom contact lens showed 1.5 lines of improvement for photopic high contrast (P=.03) and 1 line for photopic low contrast (P=.11) over a 5-mm pupil compared to habitual correction. Low and high order aberrations were reduced by 84% and 50% over a 5-mm pupil, respectively. Further improvements in performance of custom lenses may be achieved with further wavefront iterations.     

Higher-order wavefront aberrations in corneal refractive therapy.

PURPOSE: To assess the changes in higher-order (third through sixth) ocular wavefront aberrations produced by Corneal Refractive Therapy (CRT; Paragon Vision Sciences, Mesa, AZ). METHODS: Eighteen eyes of nine myopic subjects were fit with CRT contact lenses. Baseline subjective spherical refraction ranged from -2.25 to -6.00 D (mean +/- SD, -3.33 +/- 1.26 D), and baseline logarithm of the minimum angle of resolution (logMAR) best-corrected visual acuity was -0.13 +/- 0.06 (20/15 Snellen equivalent). Whole-eye ocular wavefront aberrations were measured using a previously validated Shack-Hartmann aberrometer. Measurements were taken at baseline and 1 month after treatment initiation. Nine measurements per dilated subject were taken and averaged. Zernike coefficients were used to calculate the third-, fourth-, fifth-, and sixth-order root-mean-square values for each eye for both 3- and 6-mm pupil sizes, and aberrations were averaged and compared with prior baseline readings. RESULTS: The mean (+/-SD) myopia reduction was 3.08 +/- 0.93 D, resulting in a subjective refraction of -0.22 +/- 0.38 D after 1 month of lens wear. Both logMAR uncorrected visual acuity (-0.07 +/- 0.18; 20/15- Snellen equivalent) and best-corrected visual acuity (-0.14 +/- 0.09) after CRT wear were not significantly different from baseline logMAR best-corrected visual acuity (paired two-tailed t-test; p = 0.41 and 0.65, respectively). Whole-eye aberrations showed a statistically significant increase in higher-order aberrations for both 3-mm (factor of 2.66; p = 0.01) and 6-mm pupils (factor of 2.50; p = 0.005). Each individual higher-order aberration also increased, ranging from a factor of 2.01 to 3.20 for 3-mm pupil sizes and 2.52 to 2.98 for 6-mm pupil sizes. Spherical-like aberrations (S4 and S6) increased by a factor of 1.79 for 3-mm pupil sizes and 2.42 for 6-mm pupil sizes. The Zernike coefficient most affected by CRT was spherical aberration (Z40), which increased from 0.084 +/- 0.16 to 0.39 +/- 0.16 microm (p = 0.0002) for 6-mm pupils. CONCLUSIONS: Use of current CRT lenses for the reduction of myopia increased higher-order wavefront aberrations and spherical aberration (Z40) in particular.     

Aberration generation by contact lenses with aspheric and asymmetric surfaces

PURPOSE: We explored the potential of aberration correction in the human eye by using a new generation of soft contact lenses with aspheric and asymmetric surfaces. METHODS: Soft contact lens samples were designed with one asymmetrical surface (front) and one spherical (back) to produce predetermined amounts of desired pure defocus, astigmatism, trefoil, coma, and spherical aberration. Contact lens wavefront aberrations were measured ex vivo using a Fizeau-Tolanski interferometer and compared with the in vivo wavefronts obtained by subtracting the aberrations of the eye with and without the contact lenses. These second set of measurements were obtained using a Shack-Hartmann sensor. RESULTS: We found that an aberration-free contact lens sample induced in the eye a small amount of residual aberration. We obtained a good match between the ex vivo and in vivo wavefront measurements for most of the samples of the contact lenses. CONCLUSIONS: The aberrations generated by soft contact lenses on the eye were predictable. Rotations and translations of the contact lenses with respect to correct position on the eye were, however, the main limitation for precise correction of the ocular aberrations.     

Comparison of high-order optical aberrations induced by different multifocal contact lens geometries

PURPOSE: To analyze the effects of different multifocal soft contact lens geometries on high-order ocular optical aberrations. MATERIALS AND METHODS: Thirty nonpresbyopic eyes were fitted with eight multifocal contact lenses: Soflens Multifocal High, Soflens Multifocal Low, Focus progressive, Acuvue Bifocal Add +2.00, Rythmic Multifocal Profile 1, Rythmic Multifocal Profile 2, Proclear D Add 2.00, Proclear N Add 2.00. All these contact lenses corrected the ametropia for far distance. The ocular aberrations were measured with and without each contact lens using a Hartmann-Shack aberrometer, (Zywave from Bausch and Lomb) successively after pupil dilation with one or two drops of Neo-Synephrine and wavefront decomposition in Zernike polynomials up to the 5th order. RESULTS: Odd and even aberrations increased for all the tested multifocal soft contact lenses. The most significant increase was noted for the a(4.0) Zernike coefficient. The mean value of a(4.0) without contact lens was -0.178+/-0.121 microm. The contact lenses having a central zone for near addition cause the inversion of the sign of the a(40) coefficient The central far vision contact lens leads to the opposite effect, increasing spherical positive aberrations. The most significant increase in total high-order ocular aberrations were noted for Proclear D soft contact lenses (0.396+/-0.109 microm without contact lens, 0.511+/-0.123 microm with contact lens; p<0.05, +29%), for Proclear N soft contact lenses (0.396+/-0.109 microm without contact lens, 0.568+/-0.165 microm with contact lens; p<0.05 +43%) and for Acuvue Bifocal soft contact lens (0.396+/-0.109 microm without contact lens, 0.567+/-0.162 microm with contact lens; p<0.05 +43%). CONCLUSION: Wearing multifocal contact lenses induces an increase in high-order ocular aberrations. The location of the near addition zone is related to the sign of the variation of the a(4.0) coefficient. The central near vision multifocal contact lenses seem to induce large amounts of negative spherical aberrations. The far vision contact lenses seem to induce an increase in positive spherical aberrations. The relative decentration of the lens to the pupil may explain the increase in odd high-order aberrations. These results might be useful to understand the visual complaints of patients fitted with multifocal contact lenses.     

Theoretical calculation of the longitudinal spherical aberration of rigid and soft contact lenses

Although previous investigators have attempted to calculate the longitudinal spherical aberration inherent in soft and rigid contact lenses both on and off the eye, the use of inappropriate assumptions on which to base their calculations has left the problem unresolved. In this study, the longitudinal spherical aberration of both soft and rigid contact lenses was calculated surface by surface both in air and on the eye using a two-dimensional, exact ray tracing program. The erroneous assumptions made by previous investigators were avoided by using an elliptical model for the anterior corneal surface and assuming that the posterior surfaces of soft lenses aligned exactly with the anterior corneal surface after flexure onto the eye. The results demonstrated that, with a 6-mm pupil, contact lenses induce significant levels of spherical aberration in the ocular system for soft lenses of back vertex power greater than +3.00 D or -6.00 D and for rigid lenses of powers more positive than -3.00 D. It is suggested that visual disturbance due to induced spherical aberration has not been a major clinical problem in the past because these conditions fall outside those experienced by a large proportion of the contact lens-wearing public.     

Changes in spherical aberration after lens refilling with a silicone oil

PURPOSE: It may be possible to restore accommodation to presbyopic human eyes by refilling the lens capsular bag with a soft polymer. In the present study, optical changes were measured that occurred in a pig eye model after the refilling of the capsular bag. METHODS: The optical power and spherical aberration in 10 isolated pig lenses were measured under different conditions. They were first determined by using a scanning laser ray-tracing technique over an effective pupil size of 6 mm. Second, the contours of the anterior and posterior lens surface were photographed, and a mathematical ray-tracing was performed by using a polynomial fit through the digitized surface contours, to determine optical power and spherical aberration. Third, the lenses were refilled with a silicone oil until their preoperative lens thickness was reached, and scanning laser ray-tracing, contour photography, and mathematical ray-tracing were repeated. Comparisons between the measurements were made to determine how the change from a gradient refractive index to a homogeneous refractive index influenced spherical aberration. The influence of the change in lens contour on spherical aberration after lens refilling was also studied. RESULTS: The natural lenses had a higher lens power than the refilled lenses (49.9 +/- 1.5 D vs. 36.8 +/- 1.5 D; P < 0.001). Moreover, there was a change in sign from negative spherical aberration before lens refilling (-3.6 D) to positive spherical aberration after lens refilling (7.9 D; P < 0.001). The comparison between scanning laser ray-tracing of the natural lens and mathematical ray-tracing of the photographed surface contours of the natural lens to determine the effect of refractive index substitution (i.e., replacement of a gradient refractive index by a homogeneous refractive index) showed a significant change in spherical aberration from -3.6 +/- 2.0 to 11.0 +/- 2.1 D (P < 0.001). The change in lens contour did not result in a significant change in spherical aberration (P = 0.08) before and after lens refilling with an equal refractive index. CONCLUSIONS: The lower lens power of refilled pig lenses compared to natural lenses was due to the lower refractive index of the refill material. Refilling pig lenses with the silicone oil used in this study resulted in an increase in spherical aberration. This increase was mainly caused by the change from a gradient refractive index to a homogeneous refractive index. The change in lens curvature after lens refilling did not result in an increase in spherical aberration. The influence of lens refilling on spherical aberration of human lenses must be determined in similar experiments in human eyes.     

Dynamic simulation of the effect of soft toric contact lenses movement on retinal image quality.

PURPOSE: To report the development of a tool designed to dynamically simulate the effect of soft toric contact lens movement on retinal image quality, initial findings on three eyes, and the next steps to be taken to improve the utility of the tool. METHODS: Three eyes of two subjects wearing soft toric contact lenses were cyclopleged with 1% cyclopentolate and 2.5% phenylephrine. Four hundred wavefront aberration measurements over a 5-mm pupil were recorded during soft contact lens wear at 30 Hz using a complete ophthalmic analysis system aberrometer. Each wavefront error measurement was input into Visual Optics Laboratory (version 7.15, Sarver and Associates, Inc.) to generate a retinal simulation of a high contrast log MAR visual acuity chart. The individual simulations were combined into a single dynamic movie using a custom MatLab PsychToolbox program. Visual acuity was measured for each eye reading the movie with best cycloplegic spectacle correction through a 3-mm artificial pupil to minimize the influence of the eyes' uncorrected aberrations. Comparison of the simulated acuity was made to values recorded while the subject read unaberrated charts with contact lenses through a 5-mm artificial pupil. RESULTS: For one study eye, average acuity was the same as the natural contact lens viewing condition. For the other two study eyes visual acuity of the best simulation was more than one line worse than natural viewing conditions. CONCLUSIONS: Dynamic simulation of retinal image quality, although not yet perfect, is a promising technique for visually illustrating the optical effects on image quality because of the movements of alignment-sensitive corrections.     

Relation between injected volume and optical parameters in refilled isolated porcine lenses

PURPOSE: This study was performed to elucidate the correlation between added lens refill material and enhanced lens power as well as the correlation between lens refilling volume and accommodative amplitude as determined by equatorial stretching of ex vivo refilled pigs' lenses. METHODS: Nine porcine lenses were refilled with increasing amounts of silicone oil. After each refill step, the lens power, the lens power change, and the lens thickness were measured both in the relaxed state and with a 3-mm larger ciliary body diameter. In addition, the spherical aberration of the refilled lenses was also quantified. RESULTS: Injection of 0.04 mL silicone material into the relaxed lens enhanced the lens power by 1 D. A 0.54-mm increase of the lens thickness in relaxed lenses added 1 D to the lens power. Increasing the lens refilling volume decreased the lens power changes measured at 3-mm ciliary body stretch. Spherical aberration was positive in the refilled lenses and increased with increasing lens refilling volume. CONCLUSION: The correlation found between the refilling volume and the lens power (0.04 mL D(-1)), as well as the correlation between the lens thickness and the lens power (0.54 mm D(-1)), might be important factors to be controlled in conjunction with surgery, as these also determine the lens power in the presence of this refill material. An increasing lens filling volume is associated with decreasing accommodative amplitude. The positive spherical aberration of refilled porcine lenses presents a sharp contrast to the negative aberration of natural pigs' lenses. Different lens contours and the transition from a gradient to a homogeneous refractive index might be responsible for this change in spherical aberration.     

Contact lens wear after photorefractive keratectomy: comparison between rigid gas permeable and soft contact lenses.

PURPOSE: To determine if rigid gas permeable (RGP) or soft contact lenses can be successfully worn after photorefractive keratectomy (PRK) to correct residual refractive errors. METHODS: Patients with residual stable ametropia after PRK were fit with RGP or soft lenses. Manifest refraction, corneal topography, and keratometry were performed, and post-PRK corneal haze was graded during the study visits. Contact lens fit characteristics and comfort were assessed. Lens centration, visual quality, and ocular surface status were graded, and visual acuity with contact lenses was charted. RESULTS: Eighteen patients were recruited for RGP lens fitting. The mean refractive error post-PRK was +0.80 D +/- 2.03 (range: -3.50 to+3.00 D). The mean contact lens power was -3.90 D +/- 2.03 (range: 0 to -7.00 D), and the mean contact lens base curve was 7.88 mm +/-0.16. A significant positive tear film at the site of the central ablation was noted, contributing to excessive minus lens power in all cases. Despite mild to moderate lens instability and de-centration, 14 patients reported excellent visual quality with the lenses, and pre-PRK best-corrected acuity was achieved in all patients. Twenty-five percent (4 of 16) of the patients were able to wear the lenses all day. Eleven patients were recruited for soft contact lens fitting-five from the RGP trial. The mean refractive error post-PRK was -0.64 D +/- 2.01 (range: -3.50 to +1.75D). The mean contact lens power was -0.60 D +/- 2.07 (range: -3.75 to +2.5 D), and the mean contact lens base curve was 8.33 mm +/- 0.42. Eight patients were corrected with lenses to their pre-PRK best-corrected acuity, and nine patients reported excellent visual quality with the lenses. All the patients had excellent lens centration. Thirty-six percent (four of 11) of patients were wearing the lenses all day. CONCLUSIONS: Fitting RGP lenses after PRK results in good visual acuity but may be associated with mild to moderate lens instability and decentration. Soft contact lens fitting also results in good visual acuity. Soft lenses were better tolerated by the subjects in our study because of improved lens centration and stability.     

Optical and visual performance of aspheric soft contact lenses.

PURPOSE: This study was conducted to investigate whether aspheric design soft contact lenses reduce ocular aberrations and result in better visual acuity and subjective appreciation of clinical performance compared with spherical soft contact lenses. METHODS: A unilateral, double-masked, randomized and controlled study was undertaken in which ocular aberrations and high and low contrast logMAR visual acuity were measured on myopic subjects who wore aspheric design (Biomedics 55 Evolution, CooperVision) and spherical design (Biomedics 55, CooperVision) soft contact lenses. Ten subjects who had about -2.00 D myopia wore -2.00 D lenses and 10 subjects who had about -5.00 D myopia wore -5.00 D lenses. Measurements were made under photopic and mesopic lighting conditions. Subjects were invited to grade comfort, vision in photopic and mesopic conditions, and overall impression with the two lens types on 100 unit visual analogue scales. RESULTS: There was no significant difference in high contrast or low contrast visual acuity between the two lens designs of either power under photopic or mesopic conditions. Both lens designs displayed lower levels of spherical aberration compared with the "no lens" condition under photopic and mesopic light levels (p < 0.0001); however, there were no differences in aberrations between aspheric and spherical lens designs. There were no statistically significant differences in subjective appreciation of clinical performance between lens designs or lens powers. CONCLUSIONS: At least with respect to the brand of lenses tested, the fitting of aspheric design soft contact lenses does not result in superior visual acuity, aberration control, or subjective appreciation compared with equivalent spherical design soft contact lenses.     

角膜球面像差引导下个体化IOL植入术后视觉质量

目的 评价角膜球面像差引导下个体化人工晶状体(IOL)植入术后视觉质量,并探讨这一方法的可行性.方法 前瞻性病例研究.行白内障超声乳化联合折叠式IOL植入术的年龄相关性白内障患者64例(82眼),术前1 d应用i-Trace视觉功能分析仪测量患者6.0 mm瞳孔直径下的角膜球面像差值,植入不同球面像差的IOL.根据全眼预测保留球面像差值将患者分为4组,A组:-0.15～-0.05 μm(12眼)；B组:-0.05～0.05 μm(24眼)；C组:0.05～0.15 μm(25眼)；D组:0.15～0.5 μm(21眼).术后3个月对患者进行裸眼视力及最佳矫正视力、波前像差、调制传递函数曲线及对比敏感度的检查.运用单因素方差分析、配对t检验方法对获得的数据进行统计学分析.结果 术后3个月4组之间像差值比较,B组及C组的全眼总像差及高阶像差均明显低于A组与D组,组间差异有统计学意义(F=4.453、3.699,P＜0.05).4组调制传递函数值比较,在低频5、10,高频25、30 c/d空间频率下组间差异有统计学意义(F=3.96、3.32、3.09、4.56,P＜0.05).4组对比敏感度比较,在暗视无眩光状态下的中频6.0 c/d,高频12.0、18 c/d空间频率,明视眩光状态下的高频12.0、18.0 c/d空间频率,暗视眩光状态下的所有空间频率B组与A、D组,C组与A、D组之间差异有统计学意义,且在暗视眩光状态下的中频6.0 c/d,高频12.0、18.0 c/d空间频率下C组对比敏感度值明显高于B组,组间差异有统计学意义.结论 术前测量角膜球面像差可以为白内障患者IOL的选择提供良好的依据,角膜球面像差引导下个体化IOL的植入为白内障患者术后视觉质量的提高提供了新的思路和方向.     

Wavefront aberration and its relationship to the accommodative stimulus-response function in myopic subjects.

BACKGROUND: Autorefractors are increasingly used in myopia research because they are convenient tools to investigate aspects of the accommodation response. The degree to which the autorefractor measures are affected by ocular aberrations has been highlighted by studies that have shown changes in aberration levels through different parts of the pupil and with accommodation. We have compared accommodative accuracy as measured with a Shin-Nippon SRW 5000 autorefractor with wavefront error as measured with a Hartmann-Shack wavefront sensor to investigate how factors such as accommodation demand, ocular aberrations, and pupil size can influence autorefractor measures. METHODS: Accommodation stimulus-response curves were determined (using negative lenses) for 30 young healthy subjects (20 myopic [-0.75 to -6.00 D] and 10 emmetropic). Accommodation levels ranged from 0 to 4 D in 1 D steps. Wavefront aberrations were also determined for the same accommodation levels using a Hartmann-Shack wavefront sensor for both the subjects' natural pupil sizes and for a 2.9-mm pupil. RESULTS: For all subjects, there was a consistent increase in negative spherical aberration with increases in accommodative stimulus. However, there was no consistent change in paraxial spherocylindrical refractive correction with accommodation stimulus. For the emmetropic subjects, accommodation error as measured with the autorefractor was statistically similar to the total spherocylindrical correction for the eye as estimated by the Hartmann-Shack wavefront sensor, but only for a 2.9-mm pupil (the pupil size utilized by the autorefractor). For the myopic subjects, accommodation error as measured with the autorefractor was statistically similar to the higher-order aberrations, but only when measured for a natural pupil size. CONCLUSIONS: The relationship between the accommodation accuracy as measured with the autorefractor and the total wavefront aberration as measured with a Hartmann-Shack wavefront sensor is largely influenced by the higher-order (fourth and above) aberration levels. For the emmetropic subjects, the errors measured by the two methods agree when adjusted to measure at similar pupil sizes. For the myopic subjects with similar pupil sizes, however, the Hartmann-Shack wavefront sensor underestimates the accommodation error at higher accommodation levels (2 to 4 D) compared with the autorefractor.     

Theoretical calculation of a contact lens thickness designed to correct the eye's monochromatic aberrations.

PURPOSE: The aim of this work is the theoretical study of high order aberration compensation in the human eye. METHODS: This compensation should be achieved with uneven thickness contact lenses (rigid gas permeable or soft), capable of inducing a localized delay on the aberrated wavefront, so that light beams originated on a point object would reach the retina at a common point, irrespective of their point of passage through the pupil. RESULTS: The algorithm for optimal local contact lens thickness determination is explained. For this purpose the aberrated wavefront measured on a patient by the double-pass technique was expressed in terms of Zernike polynomials. The knowledge of the wave aberration as a function of the point of passage through the pupil allows determination of the delay to be introduced in order to produce a wavefront as would result from non-aberrated eye, where all rays would reach the same point on the retina. CONCLUSIONS: The explanation of how it would be possible to correct wavefront deviations, by varying an RGP or soft contact lens thickness, was made, and a particular eye exemplify.     

Inefficacy of aspheric soft contact lenses for the correction of low levels of astigmatism.

PURPOSE: The purpose of this article is to compare the visual performance of a toric soft (TS) contact lens (SofLens 66 Toric; Bausch & Lomb, Rochester, NY), an aspheric soft (AS) contact lens (Frequency Aspheric; CooperVision, Fairport, NY) and a spectacle correction (SC) in subjects with low levels of astigmatism. METHODS: One eye of 30 subjects with refractive astigmatism of -0.75 DC or -1.00 DC was tested. After pupil dilation, each subject was fitted with all three forms of correction in random order. Subjects were masked from the contact lens type. High-contrast visual acuity (HCVA) and low-contrast visual acuity (LCVA) were recorded for each correction using 2-mm, 4-mm, and 6-mm artificial pupils. RESULTS: With a 2-mm pupil, HCVA was similar for the TS lens and the SC (p = 0.13); better HCVA was demonstrated with the TS lens than with the AS lens (p = 0.001). With 4-mm and 6-mm pupils, HCVA was poorer with the AS lens than with the SC (p < 0.002) and TS lenses (p < 0.0001). The difference in HCVA between the TS and AS lenses was two letters, three letters, and one line with pupil sizes of 2 mm, 4 mm, and 6 mm, respectively. LCVA was similar for the three refractive conditions with the 2-mm pupil size. With 4-mm and 6-mm pupils, LCVA was similar for the TS lens and SC, but better than the AS lens by approximately one line in each case (all p < 0.0001). CONCLUSIONS: For small pupil sizes, there is little difference in HCVA and LCVA between various refractive corrections. However, for larger pupils, HCVA and LCVA are superior with TS contact lenses and SC versus AS contact lenses by approximately a half-line or more, which is considered to be clinically significant. Superior vision can be achieved for low astigmatic contact lens wearers using TS rather than AS contact lenses.     

Objective assessment of aberrations induced by multifocal contact lenses in vivo.

PURPOSE: This study examined the effects of a soft multifocal progressive contact lens on individual Zernike coefficients describing the aberrations of the eye. METHODS: Ocular wavefront aberrations (OWA) of 10 subjects not wearing contact lenses were quantified using a Shack-Hartmann aberrometer and were repeated after lens insertion (two lenses,+2 diopters [D], and -2D distance power, order of insertion was randomized). All data were captured and stored on computer. Each coefficient of the Zernike polynomials representing, coma, spherical aberration (SA), and the fifth-order aberrations were evaluated for each OWA. Pupil size was monitored using an infrared device. RESULTS: After subjecting the data to various permutations, the following relationships and chief findings were detected: (1) Comparing coefficients with and without lenses, significant correlations for coma (Z(1)3 [rho,theta], P=0.0056; -2D and P=0.0399, +2D); SA (Z(0)4 [rho,theta], P=0.0006; -2D; and P=0.0061,+2D). Fifth-order aberration (Z(-1)5 [rho,theta], P= 0.0029,+2D). (2) With the -2D lens, the average root-mean-square (RMS) value for the SA coefficient Z(4)4 (rho,theta) and fifth-order Z(-3)5 (rho,theta) increased (P=0.045 and 0.0392, respectively). (3) With the +2D lens, the average RMS value for fifth-order coefficient Z(1)5(rho,theta) increased (P=0.0278). (4) Coma (Z(1)3 [rho,theta] coefficient) correlated with pupil size (P<0.05). Initial mean (+/-SD) pupil size (mm) was 3.05 (0.499), and this did not change significantly. CONCLUSIONS: Z(1)3(rho,theta) and Z(0)4(rho,theta) coefficients may be useful objective markers of success or failure for such contact lenses. The -2D lens had a more predictable effect on SA compared with the +2D lens design. The opposite occurs when considering the effects on the higher fifth-order order aberrations.     

Comparison of wavefront aberrations and optical quality of eyes implanted with five different intraocular lenses

PURPOSE: We compared corneal and total higher order wavefront aberrations in 25 pseudophakic eyes implanted with five different types of intraocular lenses to obtain an objective evaluation of the optical quality of these pseudophakic eyes. Five IOLs per type were studied. METHODS: Implanted lenses were the Pharmacia Tecnis Z9000 with negative spherical aberration, Pharmacia 911 Edge, Alcon Acrysof SA60AT and MA60BM, and Allergan Sensar AR40e. Eyes were examined using the Topcon KR-9000PW topographer/aberrometer, which obtains simultaneous coaxial measurements of corneal and ocular aberrations, and displays the calculated Point Spread Function (PSF) and Modulation Transfer Function (MTF). RESULTS: Corneal spherical aberration was positive in all tested eyes. For a 4-mm optical zone, ocular spherical aberration was 0.0054+/-0.0172 microm root-mean-square (RMS) in eyes implanted with the Tecnis lens, and was 0.0562 to 0.0974 microm RMS in eyes implanted with the four other conventional IOLs. A myopic refractive shift with mydriasis of -0.08 D occurred with the Tecnis IOL; it was -0.57 to -0.90 D with the conventional IOLs. Coma did not show a substantial reduction with any of the IOLs. Total wavefront aberrations showed nonsignificant reduction with the Tecnis lens. The PSF and the MTF also showed nonsignificant improvements over conventional IOLs. CONCLUSIONS: The optical quality of pseudophakic eyes can be measured in vivo by aberrometers. Different IOLs resulted in measurably different outcomes. In this preliminary study, compensation of the spherical aberration observed with the Tecnis lens confirmed the theoretical predictions associated with this lens and resulted in no myopic shift in refraction with mydriasis.