Pete S. Kollbaum

Validation of a clinical Shack-Hartmann aberrometer.

Purpose. To validate the accuracy, tolerance, and repeatability of the complete ophthalmic analysis system aberrometer (COAS, Wavefront Sciences Inc.) with model eyes and normal human eyes. Method. Model eyes were constructed from six polymethyl methacrylate, single-surface lenses with known characteristics. Accuracy of second-order aberrations was verified by measuring defocus and astigmatism induced by series of spherical and cylindrical trial lenses. Accuracy of higher-order aberrations was evaluated by comparing ray-tracing predictions with measured spherical aberration and coma of the aspheric model eyes. Tolerance to axial and lateral misalignment was measured by controlled displacements of the model eye relative to the aberrometer. Repeatability was tested on the same model eyes with repeated measurements taken within 1 s or within half an hour with realignment between each trial. Analyses were based on a 5-mm pupil diameter. Results. Defocus and astigmatism were accurately measured within the working range of the instrument automatic focus adjustment (e.g., measured defocus was within ±0.25 diopters over a −6.50 to +3.00 D range of refractive error). Accuracy of spherical aberration and coma agreed closely with theoretical predictions (e.g., for all six aspheric models, the mean absolute difference between predicted and measured Z40 was 0.007 &mgr;m). Axial displacements over the range ±2.5 mm had little effect on measurements for myopic and emmetropic model eyes. Also, lateral displacements over the range ±1.5 mm did not produce significant coma. The standard deviations of repeated measurements of higher-order root mean square on model eyes were <1% of the mean with repeated measures within 1 s and 10% of the mean for five individual measurements with realignment in between each. Tolerance to small lateral displacements was also observed for human eyes. Conclusion. The complete ophthalmic analysis system aberrometer can measure second-, third-, and fourth-order aberrations accurately and repeatedly on model eyes.

CHARACTERISTICS OF CORNEAL ECTASIA AFTER LASIK FOR MYOPIA

Purpose: There are numerous reports of corneal ectasia after laser in situ keratomileusis (LASIK) for myopia without a consistent definition of this condition or a definitive etiology. We conducted a retrospective analysis of published case reports to describe common characteristics of this postoperative event and compared them with findings from a group of successful LASIK patients. Methods: A MEDLINE search for “LASIK” and “ectasia” yielded 21 relevant articles published before May 2003 (n = 86 eyes, 59 patients). A comparison group (n = 103 eyes, 63 patients) was selected from a clinic-based sample of successful LASIK patients with 12 months of follow-up after treatment. Descriptive statistics are reported as median and interquartile range. Comparisons were performed using the Wilcoxon rank sum, Wilcoxon signed rank, and chi-square tests. Results: Time to diagnosis of ectasia after LASIK was 13 months (6 to 20 months). Residual myopia in the ectasia group was −3.69 D (−6.00 to −2.13 D) and was significantly greater than the comparison group, −0.38 D (−0.75 to 0.00 D), P < 0.001. After surgery, eyes with ectasia had increased corneal toricity 2.87 D (2.00 to 4.9 D) with increased oblique astigmatism 1.3 D (0.23 to 2.89 D) relative to eyes in the comparison group 0.00 D (0.00 to 0.08 D), and a loss of 2 lines (−0.5 to −6 lines) of best spectacle-corrected visual acuity (all P < 0.001). Thirty-five percent of reported cases resulted in subsequent corneal transplantation. Conclusions: Preoperative characteristics of corneal ectasia include worse visual acuity, less corneal thickness, greater residual myopia, and greater corneal toricity than nonectatic eyes. Treatment factors associated with corneal ectasia after LASIK are greater stromal ablation and less residual stromal bed thickness. Postoperative characteristics of corneal ectasia are myopic refractive error with increased astigmatism, worse spectacle-corrected visual acuity, increased corneal toricity with topographic abnormality, and progressive corneal thinning.

Utility of Short-Term Evaluation of Presbyopic Contact Lens Performance

Objectives To establish if evaluations of multifocal contact lens performance conducted at dispensing are representative of behavior after a moderate adaptation period. Methods Eighty-eight presbyopic subjects, across four clinical sites, wore each of four multifocal soft contact lenses (ACUVUE BIFOCAL, Focus Progressives, Proclear Multifocal, and SofLens Multifocal) for 4 days of daily wear. Comprehensive performance assessments were conducted at dispensing and after 4 days wear and included the following objective metrics: LogMAR acuity (contrast, 90% and 10%; illumination, 250 and 10 cd/m2; distance, 6 m, 100 cm, and 40 cm), stereopsis (RANDOT), reading critical print size and maximum speed and range of clear vision at near. Subjective assessments were made, with 100-point numerical rating scales, of comfort, ghosting (distance, near), visual quality (distance, intermediate, and near), and the appearance of haloes. At two sites, subjects (n = 39) also rated visual fluctuation (distance, intermediate, and near), facial recognition, and overall satisfaction. Results Among the objective variables, significant differences (paired t test, P<0.05) between dispensing and 4 days were found only for range of clear vision at near (2.9 ± 2.0 cm; mean difference ± standard deviation) and high contrast near acuity in low illumination (−0.013 ± 0.011 LogMAR). With the exception of insertion comfort, all subjective variables showed significant decrements over the same period. Overall satisfaction declined by an average of 10.9 ± 5.1 points. Conclusions Early assessment is relatively unrepresentative of performance later on during multifocal contact lens wear. Acuity based measures of vision remain substantially unchanged over the medium term, apparently because these metrics are insensitive indicators of performance compared with subjective alternatives.

Validation of an Off-Eye Contact Lens Shack-Hartmann Wavefront Aberrometer

Purpose. To evaluate the ability of a commercially available single pass Shack-Hartmann aberrometer to evaluate contact lens aberrations. Methods. Accuracy of second-order aberration measurements was verified by measuring a series of precision calibration lenses, spectacle lenses, and contact lenses. Power measurements were compared to those expected by an independent measurement or those provided by the lens manufacturer. Accuracy of third-order aberrations was verified by systematically decentering a lens with known amounts of spherical aberration and comparing the magnitude of induced coma to that of optical theory. Fourth-order aberration accuracy was verified by comparing measured longitudinal spherical aberration values to those expected by ray tracing based on the lens design. Accuracy of lower- and higher-order aberrations was verified for measurements of lenses taken in air and within a saline-filled wet cell. Repeatability was also assessed by comparing repeated measurements of the wet cell and lens in a wet cell, before and after manipulation of that cell. Results. In all cases, measured values closely matched the expected values, generally exhibiting errors of <1%. Conclusions. The instrument demonstrates good accuracy and repeatability in measuring second-, third-, and fourth-order aberrations of contact lenses and provides the industry with an instrument for evaluating the ex vivo optical characteristics of contact lenses.

Validation of an iPad Test of Letter Contrast Sensitivity

Purpose An iPad-based letter contrast sensitivity test was developed (ridgevue.com) consisting of two letters on each page of an iBook. The contrast decreases from 80% (logCS = 0.1) to 0.5% (logCS = 2.3) by 0.1 log units per page. The test was compared to the Pelli-Robson Test and the Freiburg Acuity and Contrast Test. Methods Twenty normally sighted subjects and 20 low-vision subjects were tested monocularly at 1 m using each test wearing their habitual correction. After a 5-minute break, subjects were retested with each test in reverse order. Two different letter charts were used for both the Pelli-Robson and iPad tests, and the order of testing was varied systematically. For the Freiburg test, the target was a variable contrast Landolt C presented at eight possible orientations and used a 30-trial Best PEST procedure. Repeatability and agreement were assessed by determining the 95% limits of agreement (LoA) ±1.96 SD of the differences between administrations or tests. Results All three tests showed good repeatability in terms of the 95% LoA: iPad = ±0.19, Pelli-Robson = ±0.19, and Freiburg = ±0.15. The iPad test showed good agreement with the Freiburg test with similar mean (±SD) logCS (iPad = 1.98 ± 0.11, Freiburg = 1.96 ± 0.06) and with narrow 95% LoA (±0.24), but the Pelli-Robson test gave significantly lower values (1.65 ± 0.04). Low-vision subjects had slightly poorer repeatability (iPad = ±0.24, Pelli-Robson = ±0.23, Freiburg = ±0.21). Agreement between the iPad and Freiburg tests was good (iPad = 1.45 ± 0.40, Freiburg = 1.54 ± 0.37), but the Pelli-Robson test gave significantly lower values (1.30 ± 0.30). Conclusions The iPad test showed similar repeatability and may be a rapid and convenient alternative to some existing measures. The Pelli-Robson test gave lower values than the other tests.

Vision performance with a contact lens designed to slow myopia progression.

Purpose Recent research suggests multizone/dual-focus (DF) lens corrections may aid in controlling the progression of myopia. Recently, such a soft contact lens has become commercially available in Hong Kong (MiSight, CooperVision). The purpose of the current study was to evaluate the visual acceptability of this new lens design. Methods In a double-masked, randomized, crossover trial, 24 subjects (aged 18 to 25 years) wore MiSight contact lenses and Proclear Multifocal +2.00 diopters Add D (MF) soft contact lenses. Patient-reported outcomes (0 to 100 scale) and objective measures of visual performance were acquired for best-spectacle distance correction (BC) and with each contact lens after 1 week of daily use at HIHC (high illumination–high contrast) at distance and LILC (low illumination–low contrast) at distance, intermediate, and near. Results There were no significant differences in HIHC distance acuity between BC and either the DF or MF lens and no difference between the DF and MF lenses. However, when measured under LILC, there were significant mean differences between each study lens and BC viewed at distance and intermediate. The LILC logMAR visual acuity was not significantly different between the DF and MF lenses at any viewing distance. Although average visual quality and ghosting ratings for both DF and MF study lenses were significantly lower than habitual under all conditions, there were no significant differences between the DF and MF lenses (p = 0.448). Conclusions Good acuity, similar to that attainable with typical MF lens correction, is attainable with a new contact lens designed to control myopia progression. However, like other contact lenses that contain multiple refractive zones, some decrease in visual performance may be experienced.

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 (&lgr; = 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 (&lgr; = 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.

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.

Factors influencing the electronic capture of patient-reported contact lens performance data

PURPOSE Electronic data capture is becoming increasingly common for collecting real-time patient responses. The purpose of this study was to investigate compliance with a daily electronic questionnaire regarding night-time contact lens visual performance. METHOD Forty-eight subjects (34 females) were fit and dispensed two contralateral pairs of soft contact lenses (SCLs) for one week each. Subjects were sent a nightly e-mail at 8PM containing a secure, individualized link to an electronic questionnaire asking 30 questions of varying response styles (e.g., multiple choice, short answer, etc.) about SCL visual performance. Subjects were instructed to complete the questionnaire before going to bed. RESULTS The overall completion rate based on 676 electronic questionnaires was 95.1%. Of these, only 3.6% were completed late (<24h). The percentage of subjects completing all questionnaires was significantly higher on weekdays (96.5%; Sunday through Thursday) than on weekends (91.1%; Friday and Saturday). Fisher exact tests indicated no significant association with gender for either weekday (p=0.25) or weekend (p=0.73). Although odds ratio estimates suggested that participants 23 and older were more likely to complete the questionnaire (weekday: OR=4.39, p=0.10; weekend: OR=2.93, p=0.19), these associations did not reach statistical significance. CONCLUSIONS E-mail based questionnaires provide an effective method for acquiring time specific responses, making them a viable clinical and research tool. The day(s) of the week on which assessments occur need to be strongly considered, as on-time compliance may be affected on weekend evenings, or possibly situations in which a typical schedule may not be followed.

Reducing starbursts in highly aberrated eyes with pupil miosis

To test the hypothesis that marginal ray deviations determine perceived starburst sizes, and to explore different strategies for decreasing starburst size in highly aberrated eyes.