Monochromatic aberrations and characteristics of retinal image quality

Comparison of visual performance and image quality between a myopia-control contact lens and a single-vision contact lens

OBJECTIVE

This study aimed to evaluate the visual performance and image quality of concentric dual-focus-designed contact lenses (CLs) compared with single-vision CLs in myopic Chinese people.

METHODS

Twenty myopic volunteers aged between 18 and 26 years were recruited at a university eye hospital to wear both defocus-incorporated soft contact (DISC) lenses and single-vision CLs for 1 week in random order. High- and low-contrast visual acuity (VA), contrast sensitivity (CS), ocular higher-order aberrations (HOA), Strehl ratio and the Quality of Vision (QoV) questionnaire were assessed with each type of CL at weekly follow-up.

RESULTS

Distance VA was not affected by DISC lenses compared to single-vision CLs in either high (p = 0.414) or low contrast (p = 0.431). However, there was a significant reduction in low-contrast near VA with DISC lenses compared with single-vision CLs (p = 0.011). The differences of CS between DISC lenses and single-vision CLs were significantly associated with lighting conditions and spatial frequencies (F = 128.81, P < 0.001). Compared with single-vision CLs, wavefront aberrations of DISC lenses were significantly increased in total HOA, trefoil, and spherical aberrations for either 3.0 mm or 6.0 mm pupil size. The Strehl ratio wearing DISC lenses reduced significantly compared to the single-vision CLs (p < 0.001) at a pupil diameter of 6.0 mm. QoV scores were higher overall (p = 0.026) and frequency (p = 0.019) with DISC lenses than with single-vision CLs, indicating poorer visual performance.

CONCLUSION

DISC lenses provide satisfactory distance VA. However, the higher scores of the QoV questionnaire with DISC lenses may be related to decreased CS at medium or high spatial frequencies and increased higher-order aberrations.

Image Quality Analysis of Eyes Undergoing LASER Refractive Surgery

Laser refractive surgery for myopia increases the eye’s higher-order wavefront aberrations (HOA’s). However, little is known about the impact of such optical degradation on post-operative image quality (IQ) of these eyes. This study determined the relation between HOA’s and IQ parameters (peak IQ, dioptric focus that maximized IQ and depth of focus) derived from psychophysical (logMAR acuity) and computational (logVSOTF) through-focus curves in 45 subjects (18 to 31yrs) before and 1-month after refractive surgery and in 40 age-matched emmetropic controls. Computationally derived peak IQ and its best focus were negatively correlated with the RMS deviation of all HOA’s (HORMS) (r≥-0.5; p<0.001 for all). Computational depth of focus was positively correlated with HORMS (r≥0.55; p<0.001 for all) and negatively correlated with peak IQ (r≥-0.8; p<0.001 for all). All IQ parameters related to logMAR acuity were poorly correlated with HORMS (r≤|0.16|; p>0.16 for all). Increase in HOA’s after refractive surgery is therefore associated with a decline in peak IQ and a persistence of this sub-standard IQ over a larger dioptric range, vis-à-vis, before surgery and in age-matched controls. This optical deterioration however does not appear to significantly alter psychophysical IQ, suggesting minimal impact of refractive surgery on the subject’s ability to resolve spatial details and their tolerance to blur.

Influence study of solving correction forces caused by fitting errors for thin meniscus mirror

The actuator influence functions of a thin meniscus mirror can be expanded in Zernike polynomials. And the correctness of influence functions has a great effect on solving the correction forces. The Zernike coefficients are applied as parameters in the all-floating support system. We analyze the main interferential factors when different deformation modes are corrected. The influence caused by fitting errors is studied in this paper. A preferable result can be obtained after eliminating the interferential factors. The method can obtain useful correction forces. Comparing the peak-to-valley and root mean square values among the results calculated by different accuracy influence functions, we find that there is a limited convergence property when the accuracy increases.

A preliminary investigation into the effects of ocular lubricants on higher order aberrations in normal and dry eye subjects

PURPOSE

To study the effects of ocular lubricants on higher order aberrations in normal and self-diagnosed dry eyes.

METHODS

Unpreserved hypromellose drops, Tears Again™ liposome spray and a combination of both were administered to the right eye of 24 normal and 24 dry eye subjects following classification according to a 5 point questionnaire. Total ocular higher order aberrations, coma, spherical aberration and Strehl ratios for higher order aberrations were measured using the Nidek OPD-Scan III (Nidek Technologies, Gamagori, Japan) at baseline, immediately after application and after 60 min. The aberration data were analyzed over a 5mm natural pupil using Zernike polynomials. Each intervention was assessed on a separate day and comfort levels were recorded before and after application. Corneal staining was assessed and product preference recorded after the final measurement for each intervention.

RESULTS

Hypromellose drops caused an increase in total higher order aberrations (p=<0.01 in normal and dry eyes) and a reduction in Strehl ratio (normal eyes: p=<0.01, dry eyes p=0.01) immediately after instillation. There were no significant differences between normal and self-diagnosed dry eyes for response to intervention and no improvement in visual quality or reduction in higher order aberrations after 60 min. Differences in comfort levels failed to reach statistical significance.

CONCLUSION

Combining treatments does not offer any benefit over individual treatments in self-diagnosed dry eyes and no individual intervention reached statistical significance. Symptomatic subjects with dry eye and no corneal staining reported an improvement in comfort after using lubricants.

Quantification of ghosting produced with presbyopic contact lens correction

OBJECTIVES

The defocused portion of the image obtained in wearers of bifocal and multifocal contact lenses often appears as a "ghost." Relatively few methods exist to quantify the ghosting perceived with lenses. The purpose of this study is to validate and implement a questionnaire to help patients quantify the ghost images perceived with bifocal or multifocal corrections.

METHODS

Ten subjects viewed simulated bifocal vision images displayed on a monitor. Images contained a focused and a defocused (ghost) component of a specific dimension (direction, position offset, intensity, and focus). Using a test card, the subjects identified the ghosting dimension level displayed on the monitor. An additional 54 presbyopic subjects wearing a multifocal correction monocularly viewed a well-focused stimulus and then compared the perceived image to that of the other well-corrected eye looking at the ghosting test card to quantify their visual experience of the 4 proposed ghosting dimensions.

RESULTS

Regardless of ghost letter size and orientation, subject responses were within 1 rating unit of expected on >95% of all trials for all 4 dimensions when asked to directly match a single dimension of ghosting. With bifocal images containing random amounts of these 4 dimensions most response errors were also within ± 1 unit. In presbyopes wearing a multifocal lens, the focus dimension was most strongly associated with overall ratings of ghosting.

CONCLUSIONS

The subjects can accurately and reliably report on ghost intensity, focus, direction and position offset, and well-focused ghosts are most correlated with the overall perceptual saliency of ghosting.

The Charles F. Prentice Award Lecture 2005: Optics of the Human Eye: Progress and Problems

The history of measurements of ocular aberration is briefly reviewed and recent work using much-improved aberrometers and large samples of eyes is summarized. When on-axis, higher-order, monochromatic aberrations are averaged, undercorrected, positive, fourth-order spherical aberration dominates; other Zernike wavefront aberration coefficients have average values near zero. Individually, however, many eyes show substantial amounts of third-order and other fourth-order aberrations; the value of these varies idiosyncratically about zero. Most normal eyes show only small amounts of axial monochromatic aberration for photopic pupils up to around 3 mm; the limits to retinal image quality are then usually set by diffraction, uncorrected or imperfectly corrected spherocylindrical refractive error, accommodation error, and chromatic aberration. Longitudinal chromatic aberration varies very little across the population. With larger mesopic and scotopic pupils, monochromatic aberration plays a more important optical role, but overall visual performance is increasingly dominated by neural factors. Some remaining problems in measuring and modeling the eye's optical performance are discussed.