Konrad Pesudovs

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Konrad Pesudovs is Foundation Professor and Chair of Discipline of Optometry and Vision Science at Flinders University. His main research interest is ophthalmology outcomes research; incorporating optical, visual and patient-centred measurement into the holistic measurement of outcomes in ophthalmology.

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    Assessment of surgically induced astigmatism: toward an international standard II [comment.] [Post print]
    (Elsevier, 1998-12) Goggin, M ; Pesudovs, Konrad
    Letter in response to Holladay JT, Dudega DR, Koch DD "Evaluating and reporting astigmatism for individual and aggregate data", Journal of Cataract and Refractive Surgery, 1998, vol 24, 57-65
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    Assessment of surgically induced astigmatism: toward an international standard. [comment.] [Post print]
    (Elsevier, 1998-12) Goggin, M ; Pesudovs, Konrad
    Letter that recommends minimun data sets to be reported in studies of the changes in astigmatism brought about by surgery.
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    Changes in quality of life after laser in situ keratomileusis for myopia [Post print]
    (Elsevier, 2005-08) Garamendi, Estibaliz ; Pesudovs, Konrad ; Elliott, David B
    PURPOSE: To measure quality of life (QoL) outcome in prepresbyopic myopic patients having laser in situ keratomileusis (LASIK) refractive surgery using the Quality of Life Impact of Refractive Correction (QIRC) questionnaire and to compare the QoL of preoperative patients with a sample of spectacle and contact lens wearers not considering refractive surgery. SETTING: Department of Optometry, University of Bradford, Bradford, and Ultralase, Leeds, West Yorkshire, United Kingdom. METHODS: The validated QIRC questionnaire was prospectively completed by 66 patients before and 3 months after LASIK. Patients had myopia greater than 0.50 diopters (D) (range --0.75 to --10.50 D) and were aged 16 to 39 years. Patients were also directly asked to evaluate their QoL after surgery. RESULTS: Overall QIRC scores improved after LASIK from a mean of 40.07+/- 4.30 (SD) to 53.09+/- 5.25 (F(1,130)=172.65, P<.001). Greater improvements occurred in women (53.83+/- 5.46) than in men (49.39+/- 5.94; F(1,64)=9.37, P<.005). Overall, 15 of the 20 questions (especially convenience, health concerns, and well-being questions) showed significantly improved scores (P<.05). Patients who "strongly agreed" (53.96+/- 4.91, n=33) or "agreed" (51.78+/- 6.19, n=23) had improved QoL and had significantly higher QIRC scores than those who "neither agreed nor disagreed" (44.36+/- 4.97, n=5) or "strongly disagreed" (42.82, n=1) (F(1,60)=11.24, P<.001). The matched group not contemplating LASIK scored 42.41 +/- 3.89 on QIRC overall. CONCLUSIONS: Large improvements in QIRC QoL scores were found after LASIK for myopia in the majority of patients, with greater improvements in women. A small number of patients (4.5%) had decreased QIRC QoL scores, and these were associated with complications. People presenting for LASIK scored measurably poorer than matched patients not contemplating refractive surgery.
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    Comparison of autologous serum eye drops with conventional therapy in a randomised controlled crossover trial for ocular surface disease
    (BMJ Publishing Group - http://bjo.bmjjournals.com/, 2004-05) Noble, Bruce A ; Loh, Raymond S K ; MacLennan, S ; Pesudovs, Konrad ; Reynolds, A ; Bridges, L R ; Burr, J
    AIMS: To evaluate the efficacy of 50% autologous serum drops against conventional treatment in ocular surface disorders refractory to normal treatments in a prospective randomised crossover trial. METHOD: Patients fulfilling ophthalmological and haematological entry criteria were randomised to either 3 months of autologous serum 50% followed by 3 months of their conventional treatment, or 3 months of conventional treatment, followed by 3 months of autologous serum. Clinical assessments, including Schirmer's test, rose Bengal, and fluorescein staining, were carried out on entry and at monthly intervals. Impression cytology was performed at entry, 3 and 6 months. Grading was carried out on degrees of squamous metaplasia and goblet cell density. Subjective comfort was recorded daily using the "faces" scale. These categorical scores were converted to linear measurement using Rasch analysis. Statistical analysis was carried out using Wilcoxon's signed rank test and ANOVA. RESULTS: 16 patients were recruited with 31 eyes studied. The ocular surface diseases chiefly included Sjogren's syndrome (n = 6) and keratoconjunctivitis sicca (n = 5). Impression cytology available in 25 of 31 eyes showed significant improvement on serum treatment, p<0.02. Rasch weighted faces scores were statistically significantly better with serum, p<0.01. CONCLUSION: The results of this randomised study provide further evidence of the beneficial effects of autologous serum in severe ocular surface disorders. For most of these patients, autologous serum was superior to conventional treatment for improving ocular surface health and subjective comfort.
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    Contrast and glare testing in keratoconus and after penetratin keratoplasty
    (BMJ Publishing Group - http://bjo.bmjjournals.com/, 2004-05) Pesudovs, Konrad ; Schoneveld, P ; Seto, R J ; Coster, Douglas John
    AIM: To compare the performance of keratoconus, penetrating keratoplasty (PK), and control subjects on clinical tests of contrast and glare vision, to determine whether differences in vision were independent of visual acuity (VA), and thereby establish which vision tests are the most useful for outcome studies of PK for keratoconus. METHODS: All PK subjects had keratoconus before grafting and no subjects had any other eye disease. The keratoconus (n = 11, age 35.0 (SD 11.1) years), forme fruste keratoconus (n = 6, 33.0 (13.0)), PK (n = 21, 41.2 (7.9)), and control (n = 24, 33.7 (8.6)) groups were similar in age. Vision testing, conducted with optimal refractive correction in place, included low contrast visual acuity (LCVA) and Pelli-Robson contrast sensitivity (PRCS) both with and without glare, as well as VA. RESULTS: Normal subjects saw better than PK subjects who in turn saw better than keratoconus subjects on all raw measures. However, when adjusted for VA, the normal group only saw significantly better than the keratoconus group on LCVA (low contrast loss 0.05 (0.04) v 0.15 (0.12), F(2,48) = 6.16; p<0.01, post hoc Sheffe p<0.05), and the decrements to glare were no worse than for normals. The forme fruste keratoconus group were indistinguishable from normals on all measures. CONCLUSIONS: PK subjects have superior vision to keratoconus subjects, but not as good as normal subjects. Including mild keratoconus subjects within a keratoconus group could confound these differences in vision. While VA is an excellent test for comparing normal, keratoconus and PK groups, additional information can be provided by LCVA and PRCS, but not by glare testing. Outcomes research into keratoconus management should include a measure in the contrast domain.
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    A Critical Flicker Fusion (CFF) test of potential vision [Post print]
    (Elsevier, 2007-02) Shankar, Hema ; Pesudovs, Konrad
    Purpose: To continue developing a potential vision test based on the critical flicker fusion (CFF) phenomenon by using a brighter stimulus and optimizing its size. Setting: The Flinders Eye Centre of the Flinders Medical Centre, Flinders University, South Australia. Methods: A prospective, non-randomized study with 225 participants (134 females, 59.8%; mean age 71.4!13.2 yrs) assigned to four groups: normal (n=41), media opacity only (n=61), retinal/neural disease only (n=61), and cataract plus retinal/neural disease (n=61). Participants were recruited into these groups if aged over 20 years, but were excluded if they had any neurological disorder or medication known to affect CFF. CFF thresholds were measured for three stimulus sizes (0.5°, 1.0°, 1.5°). Discrimination between groups was tested with ANOVA and Receiver Operating Characteristic (ROC) analysis. The relationship between visual acuity (VA) and CFF in eyes without media opacity was determined with linear regression and used to predict visual outcome of 23 eyes undergoing cataract surgery. Results: CFF thresholds were reduced in retinal/neural disease but resistant to image degradation from media opacity. The 1.5° stimulus had 88% sensitivity and 90% specificity for discriminating groups. Post-cataract surgery VA was accurately predicted within ±1 line in 43%, ±2 lines in 83% and ±3 lines in 100% of eyes All eyes with poor VA (>0.50 logMAR) or dense cataract (>4.0 LOCSIII) were predicted within ±2 lines. Conclusion: CFF effectively discriminates between subjects with and without retinal/neural disease and accurately predicts visual outcome after cataract surgery. The use of a brighter stimulus enhanced performance in dense media opacity.
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    Effect of cataract surgery incision location and intraocular lens type on ocular aberrations. [Post print]
    (Elsevier, 2005-04) Pesudovs, Konrad ; Dietze, Holger ; Stewart, Owen G ; Noble, Bruce A ; Cox, Michael J
    PURPOSE: To determine whether Hartmann-Shack wavefront sensing detects differences in optical performance in vivo between poly(methyl methacrylate) (PMMA) and foldable acrylic intraocular lenses (IOLs) and between clear corneal and scleral tunnel incisions and whether optical differences are manifested as differences in visual performance. SETTING: Department of Optometry, University of Bradford, West Yorkshire, United Kingdom. METHODS: This study comprised 74 subjects; 17 were phakic with no ocular pathology, 20 had implantation of a Pharmacia 722C PMMA IOL through a scleral tunnel, 21 had implantation of an Alcon AcrySof IOL through a scleral tunnel, and 16 had implantation of an AcrySof IOL through a corneal incision. Visual acuity and contrast sensitivity testing, ocular optical quality measurement using Hartmann-Shack wavefront sensing, and corneal surface measurement with a videokeratoscope were performed in all cases. RESULTS: There were significant differences between groups in the total root-mean-square (RMS) wavefront aberration over a 6.0 mm pupil (F=3.91; degrees of freedom=3,70; P<.05) mediated at the 4th-order RMS, specifically spherical and tetrafoil aberrations. The PMMA-scleral group had the least aberrations and the AcrySof-corneal group the most. For a 3.5 mm diameter pupil, the total higher-order RMS wavefront aberration was not significantly different between the groups (P>.05). There were no differences between groups in corneal shape, visual acuity, or contrast sensitivity. CONCLUSIONS: Implantation of the spherical PMMA IOL led to a slight reduction in total wavefront aberration compared to phakic eyes. AcrySof IOLs induced more aberrations, especially spherical aberration. Corneal-based incisions for IOL implantation compounded this increase. Studies of the optical performance of IOLs in vivo should use wavefront sensing as the main outcome measure rather than visual measures, which are readily confounded by multiple factors.
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    Geriatric Vision Care – a New Look at the Old
    (Spanish Council of Optometry, 2009) Leat, S ; Gurwood, A ; Kergoat, H ; Pesudovs, Konrad ; Eperjesi, F
    World-wide, Optometry is expanding its scope of practice in many jurisdictions. The campaign to use therapeutic pharmaceutical agents (TPAs) is on-going in most countries and optometrists are increasingly becoming involved in co-managing glaucoma and the ocular complications of diabetes, interfacing with systemic and ophthalmic specialists. Optometrists continue to define their role as members of the healthcare team by serving as post-operative care specialists following refractive and cataract surgeries. In addition, Optometry continues to be a leader in pediatric eye care and pediatric eye research, including working with children with learning disabilities and children with special needs (multiple-challenges). While low vision, contact lenses and orthoptics (vision training/binocular vision) remain staples of the traditional domain, they should not be ignored at the expense of new growth. Even as we struggle, some ask, “is the time ripe for Optometry to begin to recognize its own subspecialties?” Although all optometrists graduate as primary eye care providers, as the profession expands special interest practitioners have laid claim to areas of expertise such as sports vision specialist, rehabilitation vision specialist, neurooptometric specialty and so on. Just as medicine, and then ophthalmology before us, recognized sub-disciplines, should Optometry mature along a similar path?
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    An instrument for assessment of subjective visual disability in cataract patients
    (BMJ Publishing Group - http://bjo.bmjjournals.com/, 1998) Pesudovs, Konrad ; Coster, Douglas John
    The construction and validation of an instrument for the assessment of subjective visual disability in the cataract patient is described. This instrument is specifically designed for measuring the outcome of cataract surgery with respect to visual disability. METHODS: Visually related activities thought to be affected by cataract were considered for the questionnaire. These were reduced by pilot study and principal components analysis to 18 items. A patient's assessment of his/her ability to perform each task was scored on a four point scale. Scores were averaged to create an overall index of visual disability, as well as subscale indices for mobility related disability, distance/lighting/reading related disability, and near and related tasks visual disability. The questionnaire, administered verbally is entitled "The Visual Disability Assessment (VDA)". Reliability testing included test-retest reliability, interobserver reliability (p, the intraclass correlation coefficient), and internal consistency reliability (Cronbach's alpha). Construct validation, the process for proving that a test measures what it is supposed to measure, included consideration of content validity, comparison with the established Activities of Daily Vision Scale (ADVS) and empirical support with factor analysis. RESULTS: For the four indices, interobserver reliability varied from 0.92 to 0.94, test-retest reliability varied from 0.96 to 0.98, and internal consistency reliability varied from 0.80 to 0.93. The VDA compared favourably with the ADVS by correlation, but Bland-Altman analysis demonstrated that the two instruments were not clinically interchangeable. Factor analysis suggests that all test items measure a common theme, and the subgroupings reflect common themes. CONCLUSIONS: The VDA is easy to administer because it has a short test time and scoring is straightforward. It has excellent interobserver, test-retest, and internal consistency reliability, and compares favourably with the ADVS, another test of visual disability. Factor analysis demonstrated that the 18 items measure a related theme, which can be assumed to be visual disability. The VDA is a valid instrument which provides a comprehensive assessment of visual disability in cataract patients and is designed to detect changes within a patient over time.
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    Late onset post-keratoplasty astigmatism in patients with keratoconus
    (BMJ Publishing Group - http://bjo.bmjjournals.com/, 2004-03) Lim, L ; Pesudovs, Konrad ; Goggin, M ; Coster, Douglas John
    AIM: 10 eyes of 10 patients are reported where progression of keratoconus in the host cornea occurred more than 10 years after penetrating keratoplasty with resultant increase in astigmatism. The technique and results of graft refractive surgery in seven eyes are presented. METHODS: The clinical features and management of these patients were retrospectively analysed. Graft refractive surgery involved an incision at the graft-host junction adjacent to the host thinning with compressive resuturing. Astigmatic changes were calculated using vector analysis. RESULTS: There were seven men and three women with a mean age of 41.2 years. The average age when undergoing penetrating keratoplasty in the affected eye was 28.4 years and the average time after penetrating keratoplasty until keratoconus appeared in the host cornea defined by host thinning was 13.5 years. The mean cylinder power before host thinning was noted was 5.07 D (SD 2.19) and the mean after host thinning was 11.0 D (2.53). The mean vector calculated disease induced astigmatism magnitude was 7.59 D (3.09). Graft refractive surgery was performed in seven eyes. The mean cylinder power before and after graft refractive surgery was 11.28 D (2.15) and 7.09 D (5.53) respectively. The surgically induced astigmatism vector magnitude was 7.36 D (4.88). CONCLUSION: Progression of keratoconus in the host cornea late after penetrating keratoplasty is characterised by a large astigmatic change where the flat axis of astigmatism passes through an area of host thinning visible on slit lamp examination. Compressive resuturing performed in the area of host thinning resulted in satisfactory reduction of astigmatism.
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    Orbscan mapping in Ehlers-Danlos syndrome [Post print]
    (Elsevier, 2004-08) Pesudovs, Konrad
    A candidate for refractive surgery presented with classic (type I) Ehlers-Danlos syndrome (EDS). Clinical examination revealed blue sclera, limbus-to-limbus corneal thinning, myopia, and astigmatism. Orbscan (Bausch & Lomb)pachymetry mapping provided a striking demonstration of the limbus-to-limbus thinning with a central corneal thickness of 360 microm in the right eye and 383 microm in the left eye and midperipheral corneal thickness ranging from 370 to 438 microm and 376 to 434 microm, respectively. Despite the theoretical biomechanical weakness from the thin cornea and defective collagen, regular surface topography was maintained without the development of keratoconus. Although all types of EDS remain a contraindication to laser refractive surgery, Orbscan mapping provides a valuable insight into corneal shape and thickness in this condition.
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    Patient-centered measurement in ophthalmology - a paradigm shift
    ( 2006) Pesudovs, Konrad
    Ophthalmologists and researchers in ophthalmology understand what a rapidly evolving field ophthalmology is, and that to conduct good research it is essential to use the latest and best methods. In outcomes research, one modern initiative has been to conduct holistic measurement of outcomes inclusive of the patient's point of view; patient-centred outcome. This, of course, means including a questionnaire. However, the irony of trying to improve outcomes research by being inclusive of many measures is that the researcher may not be expert in all measures used. Certainly, few people conducting outcomes research in ophthalmology would claim to be questionnaire experts. Most tend to be experts in their ophthalmic subspecialty and probably simply choose a popular questionnaire that appears to fit their needs and think little more about it. Perhaps, unlike our own field, we assume that the field of questionnaire research is relatively stable. This is far from the case. The measurement of patient-centred outcomes with questionnaires is a rapidly evolving field. Indeed, over the last few years a paradigm shift has occurred in patient-centred measurement.
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    Patient-centred measurement in ophthalmology - a paradigm shift
    (BioMed Central - http://www.biomedcentral.com, 2006-06) Pesudovs, Konrad
    Ophthalmologists and researchers in ophthalmology understand what a rapidly evolving field ophthalmology is, and that to conduct good research it is essential to use the latest and best methods. In outcomes research, one modern initiative has been to conduct holistic measurement of outcomes inclusive of the patient's point of view; patient-centred outcome. This, of course, means including a questionnaire. However, the irony of trying to improve outcomes research by being inclusive of many measures is that the researcher may not be expert in all measures used. Certainly, few people conducting outcomes research in ophthalmology would claim to be questionnaire experts. Most tend to be experts in their ophthalmic subspecialty and probably simply choose a popular questionnaire that appears to fit their needs and think little more about it. Perhaps, unlike our own field, we assume that the field of questionnaire research is relatively stable. This is far from the case. The measurement of patient-centred outcomes with questionnaires is a rapidly evolving field. Indeed, over the last few years a paradigm shift has occurred in patient-centred measurement.
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    Refractive error changes in cortical, nuclear, and posterior subcapsular cataracts
    (BMJ Publishing Group - http://bjo.bmjjournals.com/, 2003-08) Pesudovs, Konrad ; Elliott, David B
    AIMS: To determine the effect of the three main morphological types of cataract on refractive error. METHODS: Data were prospectively collected from 77 subjects (age 67 (SD 8) years) with one morphological type of cataract. 34 had cortical, 21 had nuclear, and 21 had posterior subcapsular cataract. 22 subjects with clear lenses (60 (7) years) were recruited as controls. The spherical equivalent and astigmatic vector change between spectacle correction and optimal refraction were calculated. RESULTS: The cortical cataract group showed a significant astigmatic change of 0.71 (0.67) D (mean (1 SD)) compared to the control group (0.24 (0.20) D), with 24% outside the 95% confidence limit (0.63 D). The nuclear cataract group showed a significant myopic shift of -0.38 (0.60) D compared to the control group (+0.02 (0.21) D), with 52% beyond the minus 95% confidence limit (-0.39 D). CONCLUSION: A quarter of subjects with cortical cataract showed larger changes in astigmatism than subjects with clear lenses. This is probably because of the localised refractive index changes along cortical spoke opacities within the pupillary area. The well known myopic shift of nuclear cataract was also demonstrated.
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    Refractive Status and Vision Profile: evaluation of psychometric properties and comparison of Rasch and summated Likert-scaling. [Post-print]
    (Elsevier, 2006-04) Garamendi, Estibaliz ; Pesudovs, Konrad ; Stevens, Michael J ; Elliott, David B
    The psychometric properties of the Refractive Status and Vision Profile (RSVP) questionnaire were evaluated using Rasch analysis. Ninety-one myopic patients from a refractive surgery clinic and general optometric practice completed the RSVP. Rasch analysis of the RSVP ordinal data was performed to examine for unidimensionality and item reduction. The traditional Likert-scoring system was compared with a Rasch-scored RSVP and a reduced item Rasch-scored RSVP. Rasch analysis of the original RSVP showed poor targeting of item difficulty to patient quality of life, items with a ceiling effect and underutilized response categories. Combining the underutilized response scales and removal of redundant and misfitting items improved the internal consistency and targeting of the RSVP, and the reduced 20-item Rasch scored RSVP showed greater relative precision over standard Likert scoring in discriminating between the two subject groups. A Rasch scaled quality of life questionnaire is recommended for use in refractive outcomes research.
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    Repeatability of corneal first-surface wavefront aberrations measured with Pentacam corneal topography [Post print]
    (Elsevier, 2008-05) Shankar, Hema ; Taranath, Deepa A ; Santhirathelagan, Chandramalar T ; Pesudovs, Konrad
    PURPOSE: To assess the repeatability of corneal wavefront aberrations derived from Pentacam (Oculus) corneal topography. SETTING: Flinders Eye Centre, Flinders Medical Centre, Bedford Park, South Australia, Australia. METHODS: Forty-five normal participants and 10 participants with keratoconus were tested. Intraobserver and interobserver repeatability was determined using 4 observers within and between sessions. Topographical maps were exported to external software, and corneal first-surface wavefront aberrations were calculated using a 10th-order Zernike expansion over a 6.0 mm optical zone. Repeatability was determined with Bland-Altman limits of agreement and expressed as the coefficient of repeatability (COR). RESULTS: Initial data showed high wavefront aberrations in normal participants and poor repeatability. Topographical maps showed extrapolated topography in zones without data acquisition; maps with less than 6.0 mm of complete data were excluded in the final analysis. The mean wavefront aberrations for normal participants remained high, but repeatability improved. The COR relative to the magnitude of wavefront aberrations was high (average 100%) across all modal pairs and orders, although best for total higher-order root mean square. Participants with keratoconus had higher magnitude wavefront aberrations and poorer repeatability but similar COR to average wavefront aberration ratios. Examination of raw elevation data showed poor repeatability. CONCLUSIONS: Wavefront aberrations calculated from Pentacam corneal topography were large in magnitude, and reliability was poor, largely due to variability in corneal elevation data. Intraobserver and interobserver reliability within and between sessions was comparable. The Pentacam was not reliable in measuring corneal wavefront aberrations.
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    Shortening the VF-14 visual disability questionnaire.[comment]. [Post print]
    (Elsevier, 2006-01) Pesudovs, Konrad ; Elliott, David B
    Letter commenting on Pager, Chet K. "Assessment of visual satisfaction and function after cataract surgery." J Cataract Refract Surg. 2004 Dec;30(12):2510-6; PMID: 15617917
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    The usefulness of Vistech and FACT contrast sensitivity charts for cataract and refractive surgery outcomes research
    (BMJ Publishing Group - http://bjo.bmjjournals.com/, 2004-01) Pesudovs, Konrad ; Hazel, Charlotte A ; Doran, Robert M L ; Elliott, David B
    AIM: To investigate the repeatability and sensitivity of two commonly used sine wave patch charts for contrast sensitivity (CS) measurement in cataract and refractive surgery outcomes. METHODS: The Vistech CS chart and its descendant, the Functional Acuity Contrast Test (FACT), were administered in three experiments: (1) Post-LASIK and age matched normal subjects; (2) Preoperative cataract surgery and age matched normal subjects; (3) Test-retest repeatability data in normal subjects. RESULTS: Contrast sensitivity was similar between post-LASIK and control groups and between the Vistech and FACT charts. The percentage of subjects one month post-LASIK achieving the maximum score across spatial frequencies (1.5, 3, 6, 12, 18 cycles per degree) were (50, 33, 13, 13, 0 respectively) for FACT, but only (0, 0, 13, 4, 0 respectively) for Vistech. A small number of cataract patients also registered the maximum score on the FACT, but up to 60% did not achieve the minimum score. Test-retest intraclass correlation coefficients varied from 0.28 to 0.64 for Vistech and 0.18 to 0.45 for FACT. Bland-Altman limits of agreement across spatial frequencies were between +/-0.30 and +/-0.85 logCS for Vistech, and +/-0.30 to +/-0.75 logCS for FACT. DISCUSSION: The Vistech was confirmed as providing poorly repeatable data. The FACT chart, likely because of a smaller step size, showed slightly better retest agreement. However, the reduced range of scores on the chart due to the smaller step size led to ceiling (post-LASIK) and floor (cataract) effects. These problems could mask subtle differences between groups of patients with near normal visual function as found post-refractive or cataract surgery. The Vistech and FACT CS charts are ill suited for refractive or cataract surgery outcomes research.
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    Validity of a visual impairment questionnaire in measuring cataract surgery outcomes [post print]
    (Elsevier, 2008-06) Pesudovs, Konrad ; Caudle, Lynda Elisabeth ; Rees, Guy ; Lamoureux, Ecosse L
    PURPOSE: To test the validity of the Impact of Visual Impairment (IVI) questionnaire in a cataract population. SETTING: Flinders Eye Centre, Flinders Medical Centre, Flinders University, Adelaide, South Australia. METHODS: Cataract patients recruited from a hospital waiting list completed the IVI questionnaire. The scale was assessed for fit to the Rasch model. Unidimensionality, item and person fit to the model, response category performance, differential item functioning (whether different subgroups responded differently), and targeting of item difficulty to patient ability were assessed. RESULTS: Overall, the IVI questionnaire performed well; there were ordered thresholds, person separation reliability was 0.97, and it was free from differential item functioning. One item (worry about eyesight getting worse) misfit the model and was removed. There was evidence of multidimensionality, indicating that the overall IVI score should be discarded; however, the 3 subscales (reading and accessing information, mobility and independence, and emotional well-being) functioned well. Several items calibrated differently in cataract patients compared with low-vision patients, indicating different issues are important to each population and that there is a need for population-specific conversion algorithms. Targeting of the IVI items was biased toward more impaired patients. CONCLUSIONS: The 3 subscales of the IVI questionnaire functioned well in a cataract population. However, additional items targeting the less impaired patients, especially second-eye cataract patients, would improve measurement.
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    Validity of the Adaptation to Age-related Vision Loss Scale in an Australian Cataract Population
    (Spanish Council of Optometry, 2009) Gothwal, Vijaya ; Wright, Thomas ; Lamoureux, Ecosse L ; Pesudovs, Konrad
    Purpose: The Adaptation to Age-related Vision Loss (AVL) scale was developed to measure the adjustment of older adults who are adapting to late-life vision loss. The purpose of this study was to assess whether the AVL scale satisfies the Rasch model in a cataract population. Methods: The 24-item AVL scale (18 negatively and 6 positively coded) was mailed to 436 cataract patients for self-administration whilst they were on the waiting list for cataract surgery at the Flinders Eye Centre, Adelaide, South Australia. Rasch analysis was performed to determine whether the items were measuring a single construct (unidimensionality) as examined with fit statistics and principal components analysis (PCA) of the residuals. The ability of the scale to distinguish between the levels of adaptation of the participants (person separation) was investigated, with a value ≥ 2.0 established as the minimum acceptable. Results: The AVL scale was unable to differentiate sufficiently between participants’ levels of adaptation, indicating poor person separation. One item did not fit the construct, causing misfit. Furthermore, the five positively worded items did not appear either to measure the same construct as other items, resulting in lack of unidimensionality evidenced by PCA. Following the deletion of these items, the AVL scale was one-dimensional but a single item continued to misfit, so it had to be deleted, resulting in an 18-item AVL scale. Even so, the discriminating abilities of the scale continued to be poor. Conclusions: The AVL scale is not an appropriate measure of adaptation to vision loss in a cataract population.