A Comprehensive Evaluation of the Precision (Repeatability and Reproducibility) of the Oculus Pentacam HR

This article is made available with the permission of the publisher, Association for Research in Vision and OphthalmologyPurpose.: To evaluate the precision (repeatability and reproducibility) of the Pentacam HR (high-resolution) tomographer (Oculus, Wetzlar, Germany) across a large range of measurement parameters. Methods.: A randomly selected healthy eye of 100 subjects was scanned twice with the Pentacam HR by one observer for each of the three measurement modes: 25-picture (1 second) scan, 50-picture (2 second) scan, and cornea fine scan (50 pictures in 1 second). The repeatability of each scan mode was assessed. One additional 25-picture scan was acquired by a second observer to test reproducibility. Results.: Overall, the Pentacam HR had good precision, with the cornea fine scan returning the most precise results. The 25- and 50-picture scans showed similar precision. The repeatability limits, expressed as the within-subject SD × 1.96√2 of the anterior keratometry (K)1 and K2 readings with the standard 25-picture scan, were 0.25 and 0.36 D, respectively. Pachymetry maps, corneal maps, anterior chamber depth maps, corneal volume, topometric Q values and indices were also found to be precise. Poor precision was found for estimates of axis (astigmatic and progression index), pupil center pachymetry, single points on corneal maps, refractive power maps, and equivalent K readings. Conclusions.: Measurements taken with the Pentacam HR are repeatable and reproducible, especially those obtained with the cornea fine scan. Although the Pentacam HR is clearly a very useful clinical and research tool, the measurement of corneal axes, pupil center pachymetry, front meridional and axial maps, refractive power maps, and equivalent K readings should be interpreted with caution

Presbyopic correction use and its impact on quality of vision symptoms

Aim: To assess real-world adoption of presbyopic correction and its impact on quality of vision. Method: The use of visual corrections by 529 sequential patients (aged 36 years to 85 years, 50.4% female) attending 4 optometric practices in diverse areas across London were surveyed by interview and completed the quality of vision (QoV) questionnaire to evaluate visual symptoms. Results: Over half of the population (54.7%) managed without glasses at least some of the time, while between 30 and 40% wore distance, reading and progressive spectacles with those using Progressive Addition Lenses wearing them over 80% of the time, while those wearing reading spectacles only approximately 25% of the time. Age, sex and driving frequency had no effect of QoV (p > 0.05), whereas the distance of the task significantly impacted QoV (p < 0.01). In all QoV metrics, regardless of the far, intermediate or near blur assessment, QoV was rated higher by patients whose main tasks were far focused (n = 231, 43.9%), than those who principally conduct intermediate tasks (n = 165, 31.4%) and worse still for those whose main tasks were near (n = 130, 24.7%), regardless of the form of correction. Conclusion: Majority of tasks are in the distance and these had a higher QoV than intermediate tasks with near focused tasks being even worse. It is important to discuss with patients the principal distance of the tasks they generally perform and the forms of presbyopic correction used from the outset

Subscale Assessment of the NEI-RQL-42 Questionnaire with Rasch Analysis

This article is made available with the permission of the publisher, Association for Research in Vision and OphthalmologyPurpose.: To explore the psychometric properties of the 13 subscales of the NEI-RQL-42 questionnaire using Rasch analysis. Methods.: The NEI-RQL-42 is a refractive error-related quality of life (QoL) questionnaire with a complex design; its 13 subscales contain 42 questions, which include 16 different question/response category formats. It was completed by 100 laser refractive surgery subjects (spectacle and contact lens wearers) pre- and postoperatively. Rasch analysis was used to assess the use of response categories, success in measuring a single trait per subscale (unidimensionality), ability to discriminate persons (precision), and targeting of the questions to person QoL. Results.: Response categories were misused in four subscales (clarity of vision, diurnal fluctuation, symptoms, and appearance), which required repair before further analyses. Six subscales contained items that did not contribute to a single trait measurement (multidimensional). All subscales were found to be inadequate at distinguishing between persons (person separation >2.0), and targeting of the questions to QoL was poor for six subscales. Conclusions.: The NEI-RQL-42 questionnaire is deficient for all psychometric properties tested. Clinicians or researchers wishing to measure QoL related to refractive error correction should consider other questionnaires that have been rigorously developed and meet standard psychometric properties

Demographics, referral patterns and management of patients accessing the Welsh Eye Care Service

BACKGROUND: The Primary Eyecare Acute Referral Service (PEARS) and the Wales Eye Health Examination (WEHE) operate as enhanced optometry services for patients residing in Wales, enabling the examination of a patient presenting with an acute eye problem (PEARS) or the examination of patients at higher risk of eye disease (WEHE). The purpose of the study is to assess the demographics of patients accessing these services, referral patterns and clinical management in one Health Board in Wales (Aneurin Bevan University Health Board). METHODS: Information from 2302 patients accessing the services was prospectively collected. The following information was obtained: type of examination (PEARS or WEHE), patient age, gender, self-referral or general practitioner (GP) referral and clinical management (no further action, monitor by optometrist or ophthalmic medical practitioner [OMP], refer to the Hospital Eye Service [HES], or refer to GP). RESULTS: There were 1791 (77.8 %) PEARS examinations and 511 (22.2 %) WEHE. There were 1379 (59.9 %) females with a mean age of 58.61 (±19.75) and 923 (40.1 %) males with a mean age of 56.11 (±20.42). The majority of patients were self-referrals compared to GP-referrals (1793 [77.9 %] versus 509 [22.1 %] respectively). Sub-analysis indicated similar numbers of self-referrals compared to GP-referrals for the WEHE only (297 [58.1 %] versus 214 [41.9 %] respectively) but greater numbers of self-referrals for the PEARS examinations only (1496 [83.5 %] versus 295 [16.5 %] respectively). For management, 75 % of patients were monitored by their optometrist or OMP, 17 % required referral to the HES and 8 % required referral to their GP. CONCLUSIONS: Higher numbers of females accessed both PEARS and WEHE services and the majority of patients self-referred. These findings have important implications for public health campaigns both for targeting specific groups (e.g. male patients) and increasing awareness among GPs

Subjective Quality of Vision Before and After Cataract Surgery

This article is made available in accordance with the publisher's public repositories policy.Objective To investigate the effect of cataract surgery on subjective quality of vision. Methods The Quality of Vision (QoV) questionnaire (Italian translation) was completed before and 3 months after cataract surgery in 4 groups of patients recruited from September through December 2010: first eye with ocular comorbidity, first eye without ocular comorbidity, second eye with ocular comorbidity, and second eye without ocular comorbidity. The questionnaire measures 3 aspects of quality of vision: frequency, severity, and bothersome nature of symptoms. The Lens Opacities Classification System (LOCS) III was used for cataract grading. Friedman and Kruskal-Wallis H tests were performed to compare QoV scores within and between groups. Spearman rank correlations (rs) were calculated to investigate the correlation between LOCS III and QoV symptoms. Results Two hundred twelve patients (mean [SD] age, 74.2 [8.7] years) were recruited, and 212 eyes were included in the study. Improvements in QoV scores were found in all 4 groups (P .05) differences among the 4 groups in the improvement in QoV scores or in the preoperative or postoperative scores. Blurred vision was correlated with posterior subcapsular cataract (rs = 0.420, P = .04). Conclusions Cataract in one or both eyes causes a similar loss in subjective quality of vision, which is also irrespective of the presence of ocular comorbidity. Posterior subcapsular cataract causes the specific symptom “blurred vision.” Cataract surgery resulted in a large and comparable improvement in subjective quality of vision, regardless of ocular comorbidity and first or second eye surgery

Reengineering the Glaucoma Quality of Life-15 Questionnaire with Rasch Analysis

This article is made available with the permission of the publisher, Association for Research in Vision and OphthalmologyPurpose.: To investigate, using Rasch analysis, whether the 15-item Glaucoma Quality of Life-15 (GQL-15) forms a valid scale and to optimize its psychometric properties. Methods.: One hundred eighteen glaucoma patients (mean age, 65.7 years) completed the German-version of the GQL-15. Rasch analysis was performed to assess category function (how respondents differentiated between the response options), measurement precision (discriminative ability), unidimensionality (whether items measure a single construct), targeting (whether items are of appropriate difficulty for the sample), and differential item functioning (whether comparable subgroups respond differently to an individual item). Where any of these attributes were outside acceptable ranges, steps were taken to improve the instrument. Results.: The five-response categories of the GQL-15 were well differentiated by respondents, as demonstrated by ordered and well-spaced category thresholds. The GQL-15 had an excellent measurement precision but demonstrated poor targeting of item difficulty to person ability and multidimensionality, indicating that it was measuring more than one construct. Removal of six misfitting items created a nine-item unidimensional instrument with good measurement precision and no differential item functioning but poor targeting. A new name, the Glaucoma Activity Limitation (GAL-9) questionnaire, is proposed for the short version, which better reflects the construct under measurement. Conclusions.: The GAL-9 has superior psychometric properties over the GQL-15. Its only limitation is poor targeting of item difficulty to person ability, which is an inevitable attribute of a vision-related activity limitation instrument for glaucoma patients, most of whom have only peripheral visual field defects and little difficulty with daily activities

The Importance of Rating Scale Design in the Measurement of Patient-Reported Outcomes Using Questionnaires or Item Banks

This article is made available with the permission of the publisher, Association for Research in Vision and OphthalmologyPurpose.: To investigate the effect of rating scale designs (question formats and response categories) on item difficulty calibrations and assess the impact that rating scale differences have on overall vision-related activity limitation (VRAL) scores. Methods.: Sixteen existing patient-reported outcome instruments (PROs) suitable for cataract assessment, with different rating scales, were self-administered by patients on a cataract surgery waiting list. A total of 226 VRAL items from these PROs in their native rating scales were included in an item bank and calibrated using Rasch analysis. Fifteen item/content areas (e.g., reading newspapers) appearing in at least three different PROs were identified. Within each content area, item calibrations were compared and their range calculated. Similarly, five PROs having at least three items in common with the Visual Function (VF-14) were compared in terms of average item measures. Results.: A total of 614 patients (mean age ± SD, 74.1 ± 9.4 years) participated. Items with the same content varied in their calibration by as much as two logits; “reading the small print” had the largest range (1.99 logits) followed by “watching TV” (1.60). Compared with the VF-14 (0.00 logits), the rating scale of the Visual Disability Assessment (1.13 logits) produced the most difficult items and the Cataract Symptom Scale (0.24 logits) produced the least difficult items. The VRAL item bank was suboptimally targeted to the ability level of the participants (2.00 logits). Conclusions.: Rating scale designs have a significant effect on item calibrations. Therefore, constructing item banks from existing items in their native formats carries risks to face validity and transmission of problems inherent in existing instruments, such as poor targeting

Establishing Levels of Indications for Cataract Surgery: Combining Clinical and Questionnaire Data into a Measure of Cataract Impact

This article is made available with the permission of the publisher, Association for Research in Vision and OphthalmologyPurpose.: To develop a model for establishing indications for cataract surgery that incorporates clinical and questionnaire data on a single linear scale using Rasch analysis. Methods.: In this prospective study, 293 preoperative cataract surgery patients (mean age, 72.8 ± 10 years; age range, 33–98 years; 174 female, 119 male; 49% with ocular comorbidity) completed two questionnaires, and visual acuity was measured in each eye. A cataract impact model was developed using Rasch analysis incorporating questionnaire scores and visual acuity. Participants were ranked from 1 to 293 based on the order in which they presented (first in first out [FIFO]) and then were ranked based on the cataract impact model. The main outcome measure was the number of participants moving 49 (16.7% change) rank positions, which represented a likelihood to change priority category. Results.: The cataract impact model was unidimensional (fit statistics within 0.66–1.68) and had adequate precision (person separation of 2.58), and the components were well targeted to the population (0.05 logits between the mean item difficulty and person ability). Two hundred twenty-seven (77.5%) patients moved by at least 49 rank positions. Conclusions.: It is possible to combine clinical and questionnaire data and rank patients on a single linear scale. This approach modifies the ranking that occurs with the FIFO model and can be used for prioritizing patients for surgical intervention. More sophisticated models incorporating more clinical information may provide a better measure of the cataract impact latent trait

The development of an instrument to measure quality of vision: the quality of vision (QoV)

PURPOSE. To develop an instrument to measure subjective quality of vision: the Quality of Vision (QoV) questionnaire. METHODS. A 30-item instrument was designed with 10 symptoms rated in each of three scales (frequency, severity, and bothersome). The QoV was completed by 900 subjects in groups of spectacle wearers, contact lens wearers, and those having had laser refractive surgery, intraocular refractive surgery, or eye disease and investigated with Rasch analysis and traditional statistics. Validity and reliability were assessed by Rasch fit statistics, principal components analysis (PCA), person separation, differential item functioning (DIF), item targeting, construct validity (correlation with visual acuity, contrast sensitivity, total root mean square [RMS] higher order aberrations [HOA]), and test-retest reliability (two-way random intraclass correlation coefficients [ICC] and 95% repeatability coefficients [R c ]). RESULTS. Rasch analysis demonstrated good precision, reliability, and internal consistency for all three scales (mean square infit and outfit within 0.81-1.27; PCA Ͼ60% variance explained by the principal component; person separation 2.08, 2.10, and 2.01 respectively; and minimal DIF). Construct validity was indicated by strong correlations with visual acuity, contrast sensitivity and RMS HOA. Test-retest reliability was evidenced by a minimum ICC of 0.867 and a minimum 95% R c of 1.55 units. CONCLUSIONS. The QoV Questionnaire consists of a Raschtested, linear-scaled, 30-item instrument on three scales providing a QoV score in terms of symptom frequency, severity, and bothersome. It is suitable for measuring QoV in patients with all types of refractive correction, eye surgery, and eye disease that cause QoV problems. (Invest Ophthalmol Vis Sci. 2010;51:5537-5545) DOI:10.1167/iovs.10-5341 Q uality of vision (QoV) is a subjective entity based on an individual&apos;s unique perception of his or her vision. This perception is multifactorial, consisting not only of visual factors but also of psychological factors. Although optics and vision can be easily measured, none of these measurements explain how the patient subjectively perceives his or her vision; they provide only an indication. 1 Two patients may have identical visual function in terms of objective and subjective testing but very different perception of their QoV. Eye disease, refractive surgery, spectacles, and contact lenses may change QoV. 2-9 Therefore, the patient&apos;s perception of QoV may be an important outcome measure, but measuring perception requires a thoroughly developed and validated questionnaire. Many vision-related questionnaires have been developed, but none that specifically measures only QoV. Some instruments include QoV questions, but the questions are mixed in with the measurement of other latent traits such as visual disability. 10 -14 This combining of traits is a problem because all items that are combined to produce a score should measure a single trait; otherwise, the meaning of the measurement is unclear. 15 Second, averaging scores across all items erroneously assumes that the result provides an interval scale. It cannot be assumed that the difficulty of all questions is the same and the difficulty step between each category is constant; hence, the scaling may not be additive or linearly related to the trait under investigation. 16 Such instruments are inadequate for dealing with unanswered items and are not suitable to arithmetic functions. Item response models such as Rasch analysis have demonstrated the limitations in traditional summary (Likert) scoring 21 Rasch analysis consists of a family of psychometric models that provides a valid measurement of the latent trait, in this case, QoV, with recognized superiority over summary scoring methods. METHODS Prestudy and Questionnaire Design Items were identified via an extensive literature review and in focus groups with nonexperts and experts in the fields of refractive correction, questionnaire design, and subject interviews, to ensure content validity. The items were constructed and written at a comprehension level suitable for a 12-year-old

Meta-analysis of optical lowcoherence reflectometry versus partial coherence interferometry biometry

This work is licensed under a Creative Commons Attribution 4.0 International License. The images or other third party material in this article are included in the article’s Creative Commons license, unless indicated otherwise in the credit line; if the material is not included under the Creative Commons license, users will need to obtain permission from the license holder to reproduce the material. To view a copy of this license, visit http://creativecommons.org/licenses/by/4.0/A meta-analysis to compare ocular biometry measured by optical low-coherence reflectometry (Lenstar LS900; Haag Streit) and partial coherence interferometry (the IOLMaster optical biometer; Carl Zeiss Meditec). A systematic literature search was conducted for articles published up to August 6th 2015 in the Cochrane Library, PubMed, Medline, Embase, China Knowledge Resource Integrated Database and Wanfang Data. A total of 18 studies involving 1921 eyes were included. There were no statistically significant differences in axial length (mean difference [MD] 0 mm; 95% confidence interval (CI) −0.08 to 0.08 mm; p = 0.92), anterior chamber depth (MD 0.02 mm; 95% CI −0.07 to 0.10 mm; p = 0.67), flat keratometry (MD −0.05 D; 95% CI −0.16 to 0.06 D; p = 0.39), steep keratometry (MD −0.09 D; 95% CI −0.20 to 0.03 D; p = 0.13), and mean keratometry (MD −0.15 D; 95% CI −0.30 to 0.00 D; p = 0.05). The white to white distance showed a statistically significant difference (MD −0.14 mm; 95% CI −0.25 to −0.02 mm; p = 0.02). In conclusion, there was no difference in the comparison of AL, ACD and keratometry readings between the Lenstar and IOLMaster. However the WTW distance indicated a statistically significant difference between the two devices. Apart from the WTW distance, measurements for AL, ACD and keratometry readings may be used interchangeability with both devices