Increasing negative spherical aberration with soft contact lenses improves high and low contrast visual acuity in young adults

Combined Effect of Ocular and Multifocal Contact Lens Induced Aberrations on Visual Performance: Center-Distance Versus Center-Near Design

PURPOSE

To evaluate the combined effects of inherent ocular aberrations and induced aberrations with a multifocal soft contact lens (MFCL) after 15 days of lens wear in presbyopic participants and their influence on visual performance at distance and near under high and low contrast conditions.

METHODS

Forty presbyopic participants (mean age, 48.7±3.4) presenting a mean addition of 1.53±0.58 D were fitted with Biofinity Multifocal (CooperVision) and included in the study. Measurements comprised distance and near monocular high (100%) and low contrast (10%) logMAR visual acuity (VA). Ocular aberrations were obtained with Hartmann-Shack aberrometer (IRX3, Imagine Eyes) and analyzed for 2 mm and maximum round natural pupil.

RESULTS

Distance VA was significantly higher in dominant eye, whereas near VA was significantly better in the non-dominant eye (P<0.05 in all conditions). For a 2-mm pupil in the dominant eye fitted with MFCL, spherical-like aberration significantly increased (P=0.027) so as higher-order aberrations (HOA) (P=0.002). A significant increase was also observed in spherical-like aberrations (P=0.001), coma-like aberrations (P=0.006) and HOA (P=0.004) in non-dominant eye. For the maximum round natural pupil size, a significant decrease in vertical coma was observed (P=0.018) in dominant eye, whereas a significant increase in spherical-like (P<0.001) and coma-like aberrations (P=0.007) was observed in non-dominant eye. A negative significant correlation was found between vertical coma and high contrast VA (Rho=-0.405, P=0.011) in dominant eye; whereas in non-dominant eye, a significant correlation was found between induced secondary astigmatism and distance VA under high (Rho=0.556, P<0.001) and low contrast (Rho=0.448, P=0.005).

CONCLUSIONS

On-eye visual performance of MFSCL is dependent on the high-order aberrations induced by dominant and non-dominant design coupled with the wearer's inherent aberrations.

Test–retest reliability of contrast visual acuities in a clinical population

Background: Previously, contrast visual acuities (VA) have been evaluated as a potential screening, diagnostic and predictive tool in cases where standard visual acuity remains intact. Issues around contrast acuity sometimes make it difficult for clinicians to make appropriate clinical decisions and thus such tests have to be standardised and reliable.Aim: To investigate test–retest reliability of contrast VA in healthy adults in a clinical setting.Methods: Best compensated contrast VA at 100%, 10%, 5% and 2.5% of 155 patients (mean age 39.7 ± 12.2 years) were measured using the computerised Thomson Test Chart 2000 Expert. For all participants and at each contrast level, two measurements per right eye were determined. Test–retest reliability for the four contrast levels were assessed using reliability coefficients and Bland–Altman plots. Participants were also divided into three age groups of young (18–39 years, n = 72), middle-age (40–49 years, n = 45) and elderly (50–67 years, n = 38) and reliability was assessed within and between age and gender groups.Results: For the whole-sample test and retest, measurements within each contrast level were not statistically different (p ≥ 0.05). Thus, test and retest measurements per participant were averaged and whole-sample mean-contrast VA and standard deviations for 100%, 10%, 5% and 2.5% were -0.146 ± 0.060, 0.050 ± 0.071, 0.135 ± 0.079 and 0.405 ± 0.115 logMAR, respectively. Significant differences were found between all pairs of contrast levels compared (p ≤ 0.0125). Mean-contrast VA within each age group were also significantly different across all contrast levels (p < 0.0001). Mean-contrast VA at each contrast level between the age groups indicated that mean-contrast VA were not significantly different between the young and middle-age groups (p > 0.05) but were statistically different between the young and elderly groups (p < 0.01). Only mean-contrast VA 10% was significantly different between the middle-age and elderly groups (p < 0.001). Also, mean-contrast VA for the four contrast levels within gender were significantly different (p ≤ 0.05) but not between genders (p ≥ 0.05).Conclusion: This study found good reliability of test and retest measurements of contrast VA in an adult clinical population.

Power profiles of single vision and multifocal soft contact lenses

PURPOSE

The purpose of this study was to investigate the optical zone power profile of the most commonly prescribed soft contact lenses to assess their potential impact on peripheral refractive error and hence myopia progression.

METHODS

The optical power profiles of six single vision and ten multifocal contact lenses of five manufacturers in the powers -1.00 D, -3.00 D, and -6.00 D were measured using the SHSOphthalmic (Optocraft GmbH, Erlangen, Germany). Instrument repeatability was also investigated.

RESULTS

Instrument repeatability was dependent on the distance from the optical centre, manifesting unreliable data for the central 1mm of the optic zone. Single vision contact lens measurements of -6.00 D lenses revealed omafilcon A having the most negative spherical aberration, lotrafilcon A having the least. Somofilcon A had the highest minus power and lotrafilcon A the biggest deviation in positive direction, relative to their respective labelled powers. Negative spherical aberration occurred for almost all of the multifocal contact lenses, including the centre-distance designs etafilcon A bifocal and omafilcon A multifocal. Lotrafilcon B and balafilcon A seem to rely predominantly on the spherical aberration component to provide multifocality.

CONCLUSIONS

Power profiles of single vision soft contact lenses varied greatly, many having a negative spherical aberration profile that would exacerbate myopia. Some lens types and powers are affected by large intra-batch variability or power offsets of more than 0.25 dioptres. Evaluation of power profiles of multifocal lenses was derived that provides helpful information for prescribing lenses for presbyopes and progressing myopes.

Comparing the optical properties of soft contact lenses on and off the eye

PURPOSE

The purpose of the current study was to examine the on- and off-eye optical performance of two types of soft contact lenses (hydrogel and silicone hydrogel).

METHODS

The monochromatic aberrations (λ = 850 nm) of contact lenses were measured on-eye using a clinical Shack-Hartmann ocular aberrometer. In addition, we used an off-eye single-pass contact lens aberrometer (λ = 540 nm) in which the soft contact lens was placed within a wet cell. Comparison of the lower and higher order aberrations measured with these two methods required compensation for different wavelengths and knowledge of the refractive index of the contact lens materials.

RESULTS

The measured on-eye sphere and spherical aberration values were generally similar to those measured off-eye and those specified by the lens manufacturers for both types of soft contact lenses. However, there were notable differences, especially for high plus-powered lenses, which typically exhibited lower sphere power on the eye than expected from the lens specifications and from the off-eye measured powers, both of which were almost identical. Longitudinal spherical aberration varied with lens power in the hydrogel lenses, as expected from geometric optics theory. Longitudinal spherical aberration measurements on- and off-eye, however, deviated significantly from that expected of a thin lens with spherical surfaces due to surface asphericities. The difference between on- and off-eye optics can be modeled as a tear lens or as relative lens thickness changes caused by lens flexure.

CONCLUSIONS

The results of the current study reveal that the major difference between the on-eye lens optics and the manufacturers' specifications is not due to lens errors but due to eye-lens interactions, which could be either lens flexure or a tear lens forming behind the soft contact lens.

A randomised clinical trial to assess the effect of a dual treatment on myopia progression: the Cambridge Anti-Myopia Study

PURPOSE

To evaluate the effect of a dual treatment modality for myopia, by improving accommodative functions, on myopia progression.

METHODS

A double blind randomised control trial was conducted on 96 subjects. The treatment modality for the trial employed custom designed contact lenses which control spherical aberration in an attempt to optimise static accommodation responses during near-work, and a vision-training programme to improve accommodation dynamics. Myopia progression was assessed over a 2 year period using cycloplegic autorefraction and biometry.

RESULTS

The mean progression was found to be -0.33 Dioptres (D) over the 2 years of the study. There was no interaction between contact lens treatment and vision training treatment at 24 months (p = 0.72). There was no significant treatment effect of either Vision Training or Contact Lens Spherical Aberration control on myopia progression.

CONCLUSIONS

This study is unable to demonstrate that the progression of myopia can be reduced over a 2 year period by either of the two treatments aimed at improving accommodative function. Neither treatment group (contact lens or vision training) progressed at a slower rate over the 2 years of the study than did the appropriate control group.

Diurnal variations in visual performance for disposable contact lenses

PURPOSE

The purpose of this study is to compare the visual performance provided by different daily disposable contact lenses and to analyze its variation over time.

METHODS

Visual performance was evaluated in terms of visual acuity (VA) and contrast sensitivity (CS) in 15 myopic subjects (-0.50 to -4.00 diopters) who had been previously fitted with each one of the following seven types of soft contact lenses: DAILIES TOTAL1 (Alcon, Forth Worth, TX), DAILIES AquaComfort Plus (Alcon), 1-DAY ACUVUE TruEye (Johnson & Johnson Vision Care, Jacksonville, FL), 1-DAY ACUVUE MOIST (Johnson & Johnson Vision Care), SofLens daily disposable (Bausch & Lomb, Rochester, NY), Proclear 1 Day (CooperVision, Fairport, NY), and Clariti 1-Day (Sauflon, Twickenham, United Kingdom). We measured VA at three contrast levels (10%, 50%, and 100%) and CS for three spatial frequencies (10, 20, and 25 cycles/degree). These measurements were performed at 2-hr intervals during a 12-hr period of continuous wearing. Measurements were also performed with ophthalmic lenses before contact lens fitting.

RESULTS

Two-way analysis of variance (ANOVA) results revealed significant differences across the lens types and over time for low-contrast VA only. For high- and medium-contrast VA, ophthalmic lens performed better than the contact lenses after 12 hr of use (without statistical differences among the contact lenses). Contrast sensitivity values also showed differences across lenses for the three spatial frequencies under analysis. For each particular lens type, no CS variations were observed with wearing time. Although some of the differences were not statistically significant, we found that, for many of the VA and CS measures, ophthalmic lens and DAILIES TOTAL1 yielded better values than the 1-DAY ACUVUE TruEye and Clariti 1-Day.

CONCLUSIONS

Assessing VA at different contrasts and CS measurements allowed us to perform a visual function evaluation. Contact lens characteristics such as material and water content, among others, may be the cause of the differences in visual performance that emerged from this study. Our findings provide useful information for contact lens practitioners.

Statistical methods for conducting agreement (comparison of clinical tests) and precision (repeatability or reproducibility) studies in optometry and ophthalmology

The ever-expanding choice of ocular metrology and imaging equipment has driven research into the validity of their measurements. Consequently, studies of the agreement between two instruments or clinical tests have proliferated in the ophthalmic literature. It is important that researchers apply the appropriate statistical tests in agreement studies. Correlation coefficients are hazardous and should be avoided. The 'limits of agreement' method originally proposed by Altman and Bland in 1983 is the statistical procedure of choice. Its step-by-step use and practical considerations in relation to optometry and ophthalmology are detailed in addition to sample size considerations and statistical approaches to precision (repeatability or reproducibility) estimates.