Accuracy, Repeatability, and Clinical Application of Spherocylindrical Automated Refraction Using Time-Based Wavefront Aberrometry Measurements

Accuracy and precision of automated subjective refraction in young hyperopes under cycloplegia

PURPOSE

To assess the agreement between the Eye Refract, an instrument to perform subjective automated refraction, and the traditional subjective refraction, as the gold standard, in young hyperopes under noncycloplegic and cycloplegic conditions.

METHODS

A cross-section and randomized study was carried out, involving 42 participants (18.2 ± 7.7 years, range 6 to 31 years). Only one eye was chosen for the analysis, randomly. An optometrist conducted the refraction with the Eye Refract, while another different optometrist conducted the traditional subjective refraction. Spherical equivalent (M), cylindrical components (J0 and J45), and corrected distance visual acuity (CDVA) were compared between both refraction methods under noncycloplegic and cycloplegic conditions. A Bland-Altman analysis was performed to assess the agreement (accuracy and precision) between both refraction methods.

RESULTS

Without cycloplegia, the Eye Refract showed significantly lower values of hyperopia than the traditional subjective refraction (p < 0.009), the mean difference (accuracy) and its 95% limits of agreement (precision) being -0.31 (+0.85, -1.47) D. Conversely, there were no statistical differences between both refraction methods under cycloplegic conditions (p ≥ 0.05). Regarding J0 and J45, both refraction methods manifested no significant differences between them under noncycloplegic and cycloplegic conditions (p ≥ 0.05). Finally, the Eye Refract significantly improved CDVA (0.04 ± 0.01 logMAR) compared with the traditional subjective refraction without cycloplegia (p = 0.01).

CONCLUSIONS

The Eye Refract is presented as a useful instrument to determine the refractive error in young hyperopes, the use of cycloplegia being necessary to obtain accurate and precise spherical refraction.

Practising refraction in ophthalmology: instructive or outdated? A prospective study and literature review

CLINICAL RELEVANCE

Many ophthalmologists preform clinical refactions, although little is known of the perceptions and practise of refraction by ophthalmologists and key barriers preventing this aspect of ophthalmic practice.

BACKGROUND

Although there are numerous studies on visual acuity in ophthalmology, there is no study to date on the practice of refraction by ophthalmologists. This study evaluates the practice patterns of ophthalmologists in current practice. It specifically addresses perceptions of ophthalmologists about (a) the importance of refraction in clinical practice, and (b) barriers to performing refraction. The methodology and frequency of performing refraction by ophthalmologists is also assessed.

METHODS

This cross-sectional study was conducted at the Annual Scientific Congress of the Royal Australian and New Zealand College of ophthalmologists in 2017, held in Perth, Australia. All attending ophthalmologists and ophthalmology trainees were invited to participate. Participants completed a 17-variable questionnaire on the perceptions of practitioners about refraction and their practice of it. Data were analysed using Microsoft Excel and IBM SPSS Version 24.

RESULTS

At this Congress, 213 attendees completed the survey, with most being consultant general ophthalmologists (85%). Twenty-six percent of participants either 'really loved' or 'liked' refracting patients. Those who reported feeling competent with refraction were more likely to perform it themselves (p = 0.001). Individuals most commonly reported taking 3-5 minutes to refract a patient (38%). Participants under the age of 65, and participants practising paediatric ophthalmology, were more likely to perform a refraction.

CONCLUSIONS

The literature indicates that this is the first study to describe the practice patterns of refraction by ophthalmologists. Although ophthalmologists found refraction important, the majority preferred patients to be refracted by others. Key barriers to ophthalmologists performing refraction included the time required to perform the refraction, a busy clinic, and the availability of alternative providers.

Agreement and variability of subjective refraction, autorefraction, and wavefront aberrometry in pseudophakic patients

PURPOSE

To evaluate the comparability and variability of subjective refraction (SR), autorefraction (AR), and wavefront aberrometry (WA) in pseudophakic patients.

SETTING

Hanusch Hospital, Vienna, Austria.

DESIGN

Prospective study.

METHODS

Subjective refraction was performed by 2 independent examiners at 2 study visits. Furthermore, 5 measurements of AR and WA were performed in each patient at both visits. Agreement between the 3 refraction methods for spherical equivalent (M) and cylindrical vectors (J0, J45) was analyzed using Friedman multiple comparison and Bland-Altman plots. Predictability of spherical equivalent determined by SR from AR and WA measurements was tested with partial least squares regression and random forest regression.

RESULTS

Ninety eyes of 90 pseudophakic patients were measured. The mean absolute error and arithmetic mean difference of SR measurements of M, J0, and J45 were comparable between both examiners. A small mean difference was found for SR between both visits. Spherical equivalent was more negative when measured by AR [-0.87 diopters (D)] and WA (-0.90 D) compared with SR (-0.60 D), whereas astigmatic vectors agreed well. Good test-retest reliability was found between all 3 refraction methods for M, J0, and J45. Partial least squares regression and random forest regression showed moderate predictive power for M measured by objective refraction and SR.

CONCLUSIONS

Reproducibility and reliability of SR measurements in pseudophakic patients showed good agreement. AR and WA measured the spherical equivalent more myopic than SR, whereas astigmatic vectors were comparable between the 3 methods after uneventful cataract surgery.

Repeatability of Aberrometry-Based Automated Subjective Refraction in Healthy and Keratoconus Subjects

Purpose

To compare the intersession repeatability of the Eye Refract, a new instrument to perform aberrometry-based automated subjective refraction, on healthy and keratoconus subjects.

Materials and Methods

A cross-sectional and randomized study was performed. A total of 64 participants were evaluated in the study, selecting one eye per participant randomly. The sample was divided into two different groups: 33 healthy subjects (38.85 ± 13.21 years) and 31 with keratoconus (37.29 ± 11.37 years). Three refractions per participant with the Eye Refract were performed on three different days, without cycloplegia. The repeatability analysis of refractive variables (M, J0, and J45), binocular corrected distance visual acuity (BCDVA), and spent time in refraction was performed in terms of repeatability (S_r), its 95% confidence interval (r), and intraclass correlation coefficient (ICC).

Results

There were no statistically significant differences (P ≥ 0.05) between sessions in both groups for all refractive variables (M, J0, and J45) and BCDVA. Spent time in refraction was reduced as the sessions went by (P < 0.05). The Eye Refract was more repeatable for refractive errors assessment in healthy subjects (M : S_r = 0.27 D; J0 : S_r = 0.09 D; J45 : S_r = 0.06 D) compared to those with keratoconus (M : S_r = 0.65 D; J0 : S_r = 0.29 D; J45 : S_r = 0.24 D), while it was similar for BCDVA.

Conclusions

The Eye Refract offered better repeatability to assess refractive errors in healthy subjects compared to those with keratoconus. Despite measurements being also consistent in keratoconus subjects, they should be treated with caution in clinical practice.

Advancing Digital Workflows for Refractive Error Measurements

Advancements in clinical measurement of refractive errors should lead to faster and more reliable measurements of such errors. The study investigated different aspects of advancements and the agreement of the spherocylindrical prescriptions obtained with an objective method of measurement ("Aberrometry" (AR)) and two methods of subjective refinements ("Wavefront Refraction" (WR) and "Standard Refraction" (StdR)). One hundred adults aged 20-78 years participated in the course of the study. Bland-Altman analysis of the right eye measurement of the spherocylindrical refractive error (M) identified mean differences (±95% limits of agreement) between the different types of measurements of +0.36 D (±0.76 D) for WR vs. AR (t-test: p < 0.001), +0.35 D (± 0.84 D) for StdR vs. AR (t-test: p < 0.001), and 0.0 D (± 0.65 D) for StdR vs. WR (t-test: p < 0.001). Monocular visual acuity was 0.0 logMAR in 96% of the tested eyes, when refractive errors were corrected with measurements from AR, indicating that only small differences between the different types of prescriptions are present.

Accuracy evaluation of objective refraction using the wavefront aberrometer in pseudophakic eyes

PURPOSE

To evaluate the accuracy of wavefront-derived objective refraction in pseudophakic eyes.

METHODS

Retrospective case series. A total of 356 eyes (356 patients) that underwent phacoemulsification and posterior chamber intraocular lens implantation were included. Noncycloplegic subjective manifest refraction (MR) and objective refraction results from the wavefront aberrometer were obtained and compared. Subgroup analysis of objective refraction at 2.6-mm zone was performed based on axial length (AL) and average keratometry.

RESULTS

The biases (at the 2.6-mm, 3-mm, and 4-mm zones) were - 0.29 ± 0.37 D, - 0.53 ± 0.41 D, and - 0.51 ± 0.60 D for sphere; - 0.27 ± 0.36 D, - 0.52 ± 0.38 D, and - 0.53 ± 0.51 D for spherical equivalent (SE); 0.03 ± 0.20 D, 0.03 ± 0.22 D, and 0.04 ± 0.27 D for J₀; and 0.01 ± 0.16 D, 0.03 ± 0.22 D, and 0.01 ± 0.22 D for J₄₅, respectively. Objective refraction for sphere, SE, and J₀ (at 2.6 mm, 3 mm, and 4 mm) was significantly different from MR (P < 0.05), while J₄₅ values were equal. The objective refraction at 2.6 mm was the most accurate in short eyes (≤ 22.5 mm) with a minimum bias for SE (- 0.15 ± 0.28 D) and highest percentage of SE within ± 0.25 to ± 0.75 D of MR. However, there was no difference between the keratometry subgroups.

CONCLUSIONS

The wavefront aberrometer achieved the best accuracy at 2.6 mm in pseudophakic eyes with short AL. It still needs modification to be used as a substitute for MR in such patients.

Agreement and Repeatability of Noncycloplegic and Cycloplegic Wavefront-based Autorefraction in Children

SIGNIFICANCE

Increasing prevalence of refractive error requires assessment of ametropia as a screening tool in children. If cycloplegia is not an option, knowledge about the increase in uncertainty for wavefront-based autorefraction is needed. The cycloplegic agent as the principal variant presents cross-reference and allows for extraction of the influence of accommodation.

PURPOSE

The purpose of this study was to determine the repeatability, agreement, and propensity to accommodate of cycloplegic (ARc) and noncycloplegic (ARnc) wavefront-based autorefraction (ZEISS i.Profiler plus; Carl Zeiss Vision, Aalen, Germany) in children aged 2 to 15 years.

METHODS

In a clinical setting, three consecutive measurements were feasible for 145 eyes (OD) under both conditions. Data are described by spherical equivalent (M), horizontal or vertical astigmatic component (J0), and oblique astigmatic component (J45). In the case of M, the most positive value of the three measurements was chosen, whereas the mean was applied for astigmatic components.

RESULTS

Regarding agreement, differences for ARc minus ARnc were statistically significant: for M, 0.55 (0.55 D; mean [SD]; P < .001), that is, more hyperopic in cycloplegia; for J0, −0.03 (0.11 D; P = .002); and for J45, −0.03 D (SD, 0.09 D; P < .001). Regarding repeatability, astigmatic components showed excellent repeatability: SD < 0.11 D (ARnc) and SD < 0.09 D (ARc). The repeatability of M was SD = 0.57 D with a 95% interval of 1.49 D (ARnc). Under cycloplegia, this decreased to SD = 0.17 D (ARc) with a 95% interval of 0.50 D. The mean propensity to accommodate was 0.44 D from repeated measurements; in cycloplegia, this was reduced to 0.19 D.

CONCLUSIONS

Wavefront-based refraction measurement results are highly repeatable and precise for astigmatic components. Noncycloplegic measurements of M show a systematic bias of 0.55 D. Cycloplegia reduces the propensity to accommodate by a factor of 2.4; for noncycloplegic repeated measurements, accommodation is controlled to a total interval of 1.49 D (95%). Without cycloplegia, results improve drastically when measurements are repeated.

Comparison of Two Wavefront Autorefractors: Binocular Open-Field versus Monocular Closed-Field

Purpose

To evaluate the agreement and repeatability between a new commercially available binocular open-field wavefront autorefractor, as part of the Eye Refract system, and a monocular closed-field wavefront autorefractor (VX110).

Methods

A cross-sectional, randomized, and single-masked study was performed. Ninety-nine eyes of 99 healthy participants (37.22 ± 18.04 years, range 8 to 69 years) were randomly analyzed. Three measurements with the Eye Refract and the VX110 were taken on three different days, under noncycloplegic conditions. Mean spherical equivalent (MSE), cylindrical vectors (J0 and J45), and binocular corrected distance visual acuity (BCDVA) were compared between both autorefractors. An intersession repeatability analysis was done considering the values of repeatability (S_r) and its 95% limit (r).

Results

The VX110 showed more negative values (P < 0.001) in terms of MSE in comparison with the Eye Refract (0.20 D). Regarding cylindrical vectors, J45 showed statistically significant differences (P=0.001) between both wavefront autorefractors, but they were not clinically relevant (<0.05 D). In BCDVA, there were no statistically significant differences (P=0.667) between both wavefront autorefractors. Additionally, the Eye Refract was more repeatable than the VX110 in terms of both MSE (S_{rEYE REFRACT} = 0.21 D, S_rVX110 = 0.53 D) and J0 (S_{rEYE REFRACT} = 0.12 D, S_rVX110 = 0.35 D).

Conclusions

The Eye Refract provided enough accuracy and reliability to estimate refractive errors in different age groups, achieving better results than the VX110. Therefore, the Eye Refract proved to be a useful autorefractor to be incorporated into clinical practice.

Toric intraocular lens versus limbal relaxing incisions for corneal astigmatism after phacoemulsification

BACKGROUND

Cataract is the leading cause of blindness in the world, and clinically significant astigmatism may affect up to approximately 20% of people undergoing cataract surgery. Pre-existing astigmatism in people undergoing cataract surgery may be treated, among other techniques, by placing corneal incisions near the limbus (limbal relaxing incisions or LRIs) or by toric intraocular lens (IOLs) specially designed to reduce or treat the effect of corneal astigmatism on unaided visual acuity.

OBJECTIVES

To assess the effects of toric IOLs compared with LRIs in the management of astigmatism during phacoemulsification cataract surgery.

SEARCH METHODS

We searched CENTRAL (which contains the Cochrane Eyes and Vision Trials Register; 2019, Issue 9); Ovid MEDLINE; Ovid Embase and four other databases. The date of the search was 27 September 2019.

SELECTION CRITERIA

We included randomised controlled trials (RCTs) comparing toric IOLs with LRIs during phacoemulsification cataract surgery.  DATA COLLECTION AND ANALYSIS: We used standard methods expected by Cochrane. We graded the certainty of the evidence using GRADE. Our primary outcome was the proportion of participants with postoperative residual refractive astigmatism of less than 0.50 dioptres (D) six months or more after surgery. We also collected data on mean residual refractive astigmatism. Secondary outcomes included: uncorrected distance visual acuity, vision-related quality of life, spectacle independence and adverse effects including postoperative lens rotation requiring re-alignment. To supplement the main systematic review assessing the effects of toric IOLs compared with LRIs in the management of astigmatism during phacoemulsification cataract surgery, we sought to identify economic evaluations on the subject.

MAIN RESULTS

We identified 10 relevant studies including 517 people (626 eyes). These studies took place in China (three studies), UK (three), Brazil (one), India (one), Italy (one) and Spain (one). The median age of participants was 71 years. The level of corneal astigmatism specified in the inclusion criteria of these studies ranged from 0.75 D to 3 D. A variety of toric IOLs were used in these studies, in all but one study, these were monofocal. Studies used three different nomograms to determine the size and placement of the LRI. Two studies did not specify this. None of the studies were at low risk of bias in all domains, but two studies were at low risk of bias in all domains except selective outcome reporting, which was unclear. The remaining studies were at a mixture of low, unclear or high risk of bias. People receiving toric IOLs were probably more likely to achieve a postoperative residual refractive astigmatism of less than 0.5 D six months or more after surgery (risk ratio (RR) 1.40, 95% confidence interval (CI) 1.10 to 1.78; 5 RCTs, 262 eyes). We judged this to be moderate-certainty evidence, downgrading for risk of bias. In the included studies, approximately 500 eyes per 1000 achieved postoperative astigmatism less than 0.5 D in the LRI group compared with 700 per 1000 in the toric IOLs group. There was a small difference in residual astigmatism between the two groups, favouring toric IOLs (mean difference (MD) -0.32 D, 95% CI -0.48 to -0.15 D; 10 RCTs, 620 eyes). Although all studies favoured toric IOLs, the results of individual studies were inconsistent (range of effects -0.02 D to -0.71 D; I² = 89%). We considered this to be low-certainty evidence, downgrading for risk of bias and inconsistency. People receiving a toric IOL probably have a small improvement in visual acuity at six months or more after surgery compared to people receiving LRI, but the difference is small and probably clinically insignificant (MD -0.04 logMAR, 95% CI -0.07 to -0.02; 8 RCTs, 474 eyes; moderate-certainty evidence). Low-certainty evidence from one study of 40 people suggested little difference in vision-related quality of life measured using the Visual Function Index (VF-14) (MD -3.01, 95% CI -8.56 to 2.54). Two studies reported spectacle independence and suggested that people receiving toric IOLs may be more likely to be spectacle independent (RR 1.56, 95% CI 1.14 to 2.15; 100 people; low-certainty evidence). There were no cases of lens rotation requiring surgery (very low-certainty evidence). Five studies (320 eyes) commented on a range of other adverse effects including corneal oedema, endophthalmitis and corneal ectasia. All these studies reported that there were no adverse events with the exception of one study (40 eyes) where one participant in the LRI group had a central de-epithelisation which recovered over 10 days. We found no economic studies that compared toric IOLs with LRIs.

AUTHORS' CONCLUSIONS

Toric IOLs probably provide a higher chance of achieving astigmatism within 0.5 D after cataract surgery compared with LRIs. There may be a small mean difference in postoperative astigmatism, favouring toric IOLs, but this difference is likely to be clinically unimportant. There was no evidence of an important difference in postoperative visual acuity or quality of life between the techniques. Evidence on adverse effects was uncertain. The apparent shortage of relevant economic evaluations indicates that economic evidence regarding the costs and consequence of these two procedures is currently lacking.

Comparison of the Visual Acuity and Refractive Error Using OPDIII and Subjective Findings in Visually Normal Subjects

PURPOSE

To compare the visual acuity and refractive error using OPDIII and subjective findings in visually normal subjects.

METHOD

This study was performed on 75 participants (134 eyes) with an age range of 18 to 35 years. Visual acuity was evaluated using both subjective Snellen chart and OPDIII devices. Also, OPDIII objective refraction was compared with subjective refraction. Paired t test was used to compare mean visual acuity and refractive error. The 95% limits of agreement (LOAs) were reported to evaluate the agreement between subjective and objective methods.

RESULTS

The mean Snellen visual acuity was 0.705±0.243 logMAR in group with myopia and 0.375±0.207 logMAR in group with hyperopia. Visual acuity obtained using OPDIII was 0.632±0.270 and 0.054±0.084 logMAR in groups with myopia and hyperopia, respectively. There was a significant difference in the mean visual acuity between OPDIII and Snellen chart. The correlation of the Snellen chart with OPDIII was 0.862 and -0.172 in myopic and hyperopic groups, respectively. The 95% LOAs of the OPDIII with Snellen chart were -0.33 to 0.18 and -0.14 to 0.79 logMAR in myopic and hyperopic patients, respectively. The mean spherical power obtained by OPDIII was more negative than that of subjective refraction (OPDIII mean difference -0.272±0.335 and 0.163±0.302 DS in myopic and hyperopic groups respectively), while the cylinder power was less than that of the subjective refraction (OPDIII mean difference 0.488±0.566 and 0.030±0.255 DC in groups with myopia and hyperopia, respectively). The correlation of OPDIII with subjective refraction was 0.905, 0.920 in measurement of the spherical power and 0.908, 0.928 in measurement of the cylinder power in groups with myopia and hyperopia, respectively.

CONCLUSION

Visual acuity scores were significantly better using OPDIII compared with Snellen chart in group with myopia, whereas the Snellen chart provided the better visual acuity scores in hyperopic patients. Although the correlation of OPDIII with subjective refraction in measuring the refractive error was high, OPDIII showed a significant difference with subjective refraction.

Comparison Between Aberrometry-Based Binocular Refraction and Subjective Refraction

Purpose

We evaluate the efficacy of a new system of binocular refraction, mainly based on ocular aberrometry (EYER) and compare it with the traditional subjective refraction as gold standard.

Methods

A prospective, double blind, and transversal study was performed on 99 subjects (35 men, 64 women; mean age 37.22 ± 18.04 years; range, 7–70 years). Refractive surgery or irregular cornea were considered exclusion criteria. Subjective refraction was performed by three different optometrists and EYER by other optometrists on three different days randomly. The binocular best corrected visual acuity (BBCVA), subjective vision evaluated with visual analogue scale (VAS), refraction spent time, and mean spherical equivalent (MSE), and vertical and oblique cylindrical components (J0 and J45) were analyzed.

Results

A positive strong correlation between EYER and subjective refraction was found for MSE (Pearson, 0.984; P < 0.001) and J0 and J45 (Pearson, 0.837; P < 0.001 and Pearson, 0.852; P < 0.001, respectively) in the total group. There were no statistically significant differences for BBCVA (P < 0.05). The VAS scores were 84.29 ± 12.29 with the EYER and 86.89 ± 12.38 with subjective refraction (P = 0.031). The spent time to perform the refraction was statistically lower (P < 0.05) with the EYER compared to conventional subjective refraction for all groups.

Conclusions

The EYER system showed similar results in terms of spherical and cylindrical components, visual acuity being the spent time in the refraction lower than conventional subjective refraction.

Translational Relevance

This new objective refraction system provides less chair spent time with similar results than subjective refraction.

Precision and agreement of higher order aberrations measured with ray tracing and Hartmann-Shack aberrometers

BACKGROUND

To assess the precision and agreement of measurements of higher order aberrations (HOAs) obtained with a ray tracing aberrometer (iTrace) and a Hartmann-Shack aberrometer (Topcon KR-1 W).

METHODS

Prospective evaluation of the diagnostic test. Data from the right eyes of 92 normal subjects obtained using the two devices were included in this study. Two observers performed 3 consecutive scans to determine the intraobserver repeatability and interobserver reproducibility. About one week later, one observer performed an additional 3 consecutive scans to obtain the intersession reproducibility. The within-subject standard deviation (Sw), test-retest repeatability (TRT) and intraclass correlation coefficient (ICC) were used to assess the precision, while Bland-Altman plots were performed to assess the agreement.

RESULTS

For intraobserver repeatability of the ocular, corneal and internal HOAs, Topcon KR-1 W showed a 2.77Sw of 0.079 μm or less and ICCs of 0.761 or more; and iTrace showed a 2.77Sw of 0.105 μm or less and ICCs of 0.805 or more. The ICCs of the internal HOAs of interobserver reproducibility were less than 0.75 except for spherical aberration (SA) (0.862), and interobserver reproducibility of the counterpart showed similar but lower results. For the ocular, corneal and internal HOA measurements, statistically significant differences existed between the Topcon KR-1 W and iTrace (all P < 0.05). No significant differences were observed in the ocular SA and internal coma.

CONCLUSIONS

The ray tracing and Hartmann-Shack method aberrometers provided excellent repeatability but less reliable reproducibility in the measurement of HOAs (except for SA). The two aberrometers should not be interchangeable in clinical application because of the significant differences in HOA measurements between them.

Usefulness of refractive measurement of wavefront autorefraction in patients with difficult retinoscopy

PURPOSE

To assess the ability of the WaveScan WaveFront System (VISX Inc, Santa Clara, CA) to measure refractive errors in patients with difficult retinoscopy and to compare results to standard cycloplegic retinoscopy.

METHODS

The medical records of patients with an ocular condition that could contribute to difficult or unreliable retinoscopy who underwent nondilated, noncycloplegic evaluation with the WaveScan WaveFront System were reviewed retrospectively. Results were compared to a standard cycloplegic retinoscopy.

RESULTS

A total of 60 eyes of 31 patients were included. Wavefront sphere, cylinder, and spherical equivalent measurements were strongly correlated with retinoscopy results; however, the wavefront measured more myopia and more cylinder compared to standard retinoscopy.

CONCLUSIONS

Wavefront can be used to augment and enhance cycloplegic streak retinoscopy.

A comparison of a traditional and wavefront autorefraction

PURPOSE

To evaluate the agreement between the autorefraction function of the Canon RK-F2, an autorefractor/keratometer based on the ray deflection principle, and the Carl Zeiss Vision i.Profiler(Plus), an wavefront aberrometer, compared with each other and with a noncycloplegic subjective refraction.

METHODS

Objective refraction results obtained using both instruments were compared with noncycloplegic subjective refractions for 174 eyes of 100 participants. Analysis of sphere, cylinder, and axis using spherical equivalent difference and a new measurement, cross-cylinder difference, was performed. The spherical equivalent refraction and cross-cylinder difference for the manifest refraction were compared using Bland-Altman limits of agreement and 95th percentile analysis.

RESULTS

The 100 participants represent 52 women and 48 men with a mean (±SD) age of 51.7 (±13.8) years, an average (±SD) spherical power of -0.67 (±2.53) diopters (D), and an average (±SD) cylinder power of -0.94 (±0.87) D. The spherical equivalent difference is 0.03 D (Canon) and -0.11 D (Zeiss). The 95% limits of agreement for the spherical equivalent are -0.69 to 0.75 D (Canon) and -0.75 to 0.75 D (Zeiss). The mean cross-cylinder power difference is -0.08 D (Canon) and 0.02 D (Zeiss). The 95% limits of agreement for the cross-cylinder power difference are 0.63 to 0.50 D (Canon) and 0.49 to 0.75 D (Zeiss). The mean axis power difference is -0.04 D (Canon) and 0.05 D (Zeiss). The 95% limits of agreement for axis power difference are -0.71 to 0.63 D (Canon) and -0.78 to 0.78 D (Zeiss). The double-angle astigmatic plot center of distribution for the RK-F2 is 0.035 D at 70 degrees, and that for the i.Profiler(Plus) is 0.053 D at 32 degrees.

CONCLUSIONS

Both instruments provided clinically useful spherical equivalent refractive data compared with a subjective refraction, whereas the Canon RK-F2 was slightly more accurate in determining the cylinder power compared with a subjective refraction.

Comparison of refractive assessment by wavefront aberrometry, autorefraction, and subjective refraction

PURPOSE

To compare refractive assessment results obtained with an aberrometer, an autorefractor, and manual subjective refraction (SR) in a healthy population with optimal visual potential.

METHODS

Sixty adults aged 18-59 years with visual acuity of 20/25 or better, no media opacity, and no known corneal or retinal abnormalities were recruited during the course of routine eye examination. Refractive error in both eyes of each patient was assessed by 3 methods: manual SR, a Nidek 530-A autorefractor (AR), and a Nidek OPD-II Scan wavefront aberrometer (OPD). The order of testing was randomized. One technician collected all OPD and AR measurements, and 1 optometrist performed manual SR. Refractive measurements were converted from spherocylindrical prescriptions to power vectors and compared between methods by 2-factor repeated measures and Bland-Altman analysis.

RESULTS

Analysis of the power vectors followed by a log transformation showed no significant difference in refractive results between AR, OPD, and SR (P=.63). Bland-Altman analysis identified mean differences (95% CI of limits of agreement) of -0.06 (-0.67 to 0.55) for OPD vs SR, 0.001 (-0.522 to 0.524) for AR vs SR, and 0.06 (-0.541 to 0.662) for AR vs OPD.

CONCLUSION

Agreement between all refractive assessments was comparable to previously reported agreement between repeated measures of SR. Agreement between AR and SR was slightly stronger than between OPD and SR. Although both the OPD and AR results, in general, showed a high level of agreement with SR, results beyond ±0.50D (5.8% for AR, 10% for OPD) would discourage prescribing spectacles directly from either instrument.

Acute effect of cigarette smoking on pupil size and ocular aberrations: a pre- and postsmoking study

Aim. To evaluate the acute effects of cigarette smoking on photopic and mesopic pupil sizes and wavefront aberrations. Methods. Cigarette smoker volunteers were recruited in the study. Photopic and mesopic pupil sizes and total ocular aberrations were measured before smoking and immediately after smoking. All volunteers were asked to smoke a single cigarette containing 1.0 mg nicotine. Pupil sizes and total ocular aberrations were assessed by optical path difference scanning system (OPD-Scan II ARK-10000, NIDEK). Only the right eyes were considered for statistical analysis. The changes of pupil size and total ocular aberrations after smoking were tested for significance by Wilcoxon signed ranks test. Results. Mean photopic pupil size decreased from 3.52 ± 0.73 mm to 3.29 ± 0.58 mm (P = 0.001) after smoking. Mean mesopic pupil size was also decreased from 6.42 ± 0.75 mm to 6.14 ± 0.75 mm after smoking (P = 0.001). There was a decrease in all the measured components of aberrations (total wavefront aberration, higher-order aberration, total coma, total trefoil, total tetrafoil, total spherical aberration and total higher-order aberration) after smoking; however the differences were insignificant for all (P > 0.05). Conclusion. Our results indicate that pupil constricts after smoking. On the other hand, smoking does not alter ocular aberrations.

Back-calculation to model strategies for pretreatment adjustment of the ablation sphere in myopic wavefront laser in situ keratomileusis

PURPOSE

To examine strategies for adjusting the ablation sphere in myopic wavefront laser in situ keratomileusis (LASIK) with reference to preoperative manifest refraction.

SETTING

Refractive Surgery Service, Moorfields Eye Hospital, London, United Kingdom.

METHODS

The variance in the 3-month postoperative manifest refraction spherical equivalent (MRSE) results in 295 consecutive cases of myopic wavefront LASIK treated with a nonsystematic, intuitive approach to pretreatment adjustment of the ablation sphere was compared with the variance in modeled results obtained by back-calculation using 4 systematic strategies: (1) no adjustment (No Adj), (2) addition of the difference between the preoperative MRSE and the preoperative 4.0 mm pupil wavefront refraction spherical equivalent (WRSE) (4.0 mm), (3) addition of the difference between the preoperative MRSE and the preoperative maximum pupil WRSE (Max), and (4) addition of the difference between the preoperative MRSE and the preoperative effective blur (EB). The EB is a theoretical value for the dioptric SE of all aberrations at the pupil size calculated for the Hartmann-Shack images acquired (wavefront diameter). A stratified analysis of results for different wavefront diameters was also performed.

RESULTS

Variance in the postoperative MRSE was least (0.116) when nonsystematic, intuitive adjustments to the ablation sphere were used. In ascending order, the back-calculated variance was as follows: EB (0.142; P = .09, Bartlett test), 4.0 mm pupil (0.163; P = .004), No Adj (0.171; P = .001), and Max (0.225; P<.0001). There was a strong trend toward reduced variance in results in patients with a larger wavefront diameter.

CONCLUSION

Back-calculation to model results with different pretreatment ablation adjustment strategies may be useful to eliminate unpromising new approaches before clinical trials.

Objective and subjective preoperative refraction techniques for wavefront-optimized and wavefront-guided laser in situ keratomileusis

PURPOSE

To determine which of 3 methods for measuring preoperative refractive error yields the best refractive outcomes after wavefront-guided (Visx Star S4) or wavefront-optimized (WaveLight Allegretto Wave) excimer laser in situ keratomileusis (LASIK).

SETTING

Emory Eye Center and Emory Vision, Emory University, Atlanta, Georgia, USA.

METHODS

This retrospective analysis of LASIK, performed from June to December 2007, analyzed sphere, cylinder, and spherical equivalent (SE) refractions generated from 3 methods (manifest refraction, aberrometer autorefraction [CustomVue WaveScan], corneal analyzer autorefraction [Nidek ARK-10000 OPD]), actual programmed treatment, and absolute deviation from ideal treatment (deviation) for each technique.

RESULTS

In the wavefront-guided group (63 eyes, 33 patients), manifest refraction and aberrometer autorefraction generated similar deviation for sphere and SE; both were significantly better than corneal analyzer autorefraction (P= .02 and P= .03, respectively). Aberrometer autorefraction generated less cylinder deviation than the other methods (both P= .003). In the wavefront-optimized group (61 eyes, 36 patients), manifest refraction generated less deviation for sphere and SE than aberrometer autorefraction or corneal analyzer autorefraction (sphere: P= .005 and P= .009, respectively; SE: P= .005 and P= .002, respectively). Manifest refraction and aberrometer autorefraction cylinder generated similar deviation, while aberrometer autorefraction was less than corneal analyzer autorefraction (P= .041).

CONCLUSIONS

Overall, manifest refraction was most accurate in generating postoperative emmetropia with both laser treatments; however, aberrometer autorefraction produced the least cylinder deviation for wavefront-guided treatment. Corneal analyzer autorefraction produced the least accurate results with both lasers.

Aberration-correcting effect of ThinOptX IOL

PURPOSE

To evaluate spherical aberration and visual function after microincision cataract surgery using the ThinOptX rollable intraocular lens.

DESIGN

Prospective, comparative, and interventional case series.

METHODS

SettingSingle-centre institutional practice. This prospective study evaluated 58 patients with cataracts who underwent bimanual microphaco cataract surgery in both eyes. A ThinOptX lens was introduced into one eye and an Alcon Acrysof lens, as a control, into the other. One month after cataract surgery, the corneal, whole-eye, and internal spherical aberration, and contrast sensitivity in both eyes were measured. We also measured the spherical aberration in artificial model eyes bearing Acrysof and ThinOptX lenses. Two-sided paired t-test was used for assessing all data.

RESULTS

The root mean square (RMS) for both whole-eye and internal spherical aberrations was smaller in eyes bearing ThinOptX (P=0.03 and P=0.07, respectively). Although there was no statistically significant difference in the RMS for internal spherical aberration between ThinOptX- and Acrysof-bearing eyes, according to the Zernike polynomial expansion, all human and model eyes bearing ThinOptX registered negative internal spherical aberration in Z(4,0) and Z(6,0). On the other hand, all human and model eyes bearing Acrysof registered positive internal spherical aberration in Z(4,0) and Z(6,0). The ThinOptX lens yielded slightly higher contrast sensitivity in all cycles.

CONCLUSION

As the ThinOptX lens is designed for negative spherical aberration, we encountered smaller whole spherical aberrations and higher contrast sensitivity than with the Acrysof lens. The implantation of ThinOptX IOL after microincision cataract surgery yielded good visual function.

Validity of autorefraction after cataract surgery with multifocal ReZoom intraocular lens implantation

PURPOSE

To evaluate the clinical utility of spherocylindrical automated refraction (AR) compared with subjective manifest refraction (MR) after cataract surgery with implantation of ReZoom refractive multifocal intraocular lenses (IOLs) (Advanced Medical Optics, Inc.).

SETTING

Private Practice.

METHODS

This prospective nonrandomized interventional study consisted of 72 patients with bilateral cataract and a potential visual acuity of at least 20/40. Patients had bilateral nonsimultaneous cataract surgery and implantation of a ReZoom IOL. Manifest refraction was performed in all patients followed by 3 consecutive measurements using the Topcon KR-8000 autorefractor with nondilated and dilated pupils. Assessment of repeatability of multiple consecutive ARs and comparison of the AR and MR using power vector analysis were performed at the 6-month follow-up. The main outcome measures were the correlation between AR and MR with sphere, spherical equivalent, and astigmatism as well as the repeatability of AR before and after dilation with phenylephrine 10%.

RESULTS

Repeatability analysis showed that the initial nondilated AR was not significantly different from the mean of the 3 refractions for nondilated and dilated measurements. The mean difference between the initial AR and the MR was -0.84 +/- 0.62 diopters (D) for sphere (SD), -1.00 +/- 0.61 D for spherical equivalent, and -0.06 +/- 0.19 D and -0.01 +/- 0.17 D, respectively, for J(0) and J(45), the 2 components of astigmatism. Linear regression of AR versus MR data showed poor correlation for sphere (R(2) = 0.4852) and spherical equivalent (R(2) = 0.5529), whereas the correlation for the 2 astigmatic components of vector analysis was excellent (J(0), R(2) = 0.8881; J(45), R(2) = 0.8640). Correlation was better when the MR residual refractive defect was higher.

CONCLUSIONS

Although autorefraction showed excellent agreement with subjective refractive astigmatism, correlation with spherical values was poor, with a trend toward more negative values. Autorefraction after ReZoom IOL implantation can be used as a good starting point for subjective refraction of astigmatism; however, spherical values should be underestimated.