Stress and vision-related quality of life in acute and chronic central serous chorioretinopathy.

BACKGROUND: To compare vision-related quality of life (VRQOL) between acute and chronic Central serous chorioretinopathy (CSC) and correlate this with Cohen's Perceived Stress Scale (PSS) questionnaire. METHODS: Patients who were diagnosed with both acute and chronic CSC were recruited in this study. Vision-related quality of life (VRQOL) was assessed with Rasch revised National Eye Institute Visual Functioning Questionnaire 25 (NEI-VFQ25) and perceived stress with Cohen's PSS questionnaire in 118 subjects with either acute or chronic CSC. The quality of life score was compared between patients with acute and chronic CSC. Correlations between the functional score and visual acuity (VA), stage of CSC, and stress were studied. RESULTS: There was no significant difference in VRQOL between Acute and Chronic CSC. In Acute CSC, affected eye VA correlated significantly with near vision question of the visual function subscale. Better eye VA correlated significantly with distance vision, social function, role limitation and dependency of the socioeconomic subscale. In chronic CSC, affected eye VA correlated with social function question of the socioemotional subscale and the better eye VA correlated with driving and distance vision of the visual function subscale. No other significant correlations with VA were noted. No correlations were observed between outcome of Cohen's PSS questionnaire and NEI-VFQ25 scores of acute and chronic CSC. CONCLUSION: The VRQOL is similar between acute and chronic CSC. Perceived stress was not found to influence the VRQOL in CSC.

Parent-Child Agreement on Health-Related Quality of Life in Congenital Glaucoma.

PURPOSE: We assess parent-child agreement regarding child's health-related quality of life (HRQoL) in children operated for congenital glaucoma (CG). METHODS: A total of 121 children aged 8 to 18 years (mean age, 11.8 years) operated for CG (mean duration since surgery, 10.2 years) and their parents (mean age, 36.5 years) completed the child and parent versions of the Kidscreen-27 questionnaire, respectively. Psychometric properties of Kidscreen-27 were assessed using Rasch analysis, and child-parent agreement regarding child's HRQoL was investigated using the Bland-Altman limits of agreement (LoA) method. RESULTS: Minor modifications in the rating scale and deletion of few misfitting items resulted in a psychometrically robust Kidscreen-23 questionnaire. Average parental HRQoL score was higher than the child's own ratings, with a significant difference between their scores (mean ± standard deviation [SD] difference = 0.53 ± 2.58 logits, P = 0.02; lower LoA [95% CI], -4.52 [-5.31 to -3.72] and upper LoA [95% CI], 5.58 [4.79-6.38]). The range of child-parent agreement was wide and bidirectional, with parents tending to underestimate and overestimate their child's HRQoL. Younger children and girls showed greater discordance in their HRQoL with parental reports than adolescents and boys, respectively. CONCLUSIONS: Discordance between CG child's self-report of HRQoL and parent's report indicate that both groups perceive the broader impact of living with CG very differently. TRANSLATIONAL RELEVANCE: The HRQoL as reported by the child with CG and by his/her parent should be viewed as being complementary, rather than interchangeable. Both assessments should be taken into account in clinical practice and research studies.

Randomized Trial of Tablet Computers for Education and Learning in Children and Young People with Low Vision.

SIGNIFICANCE: Mobile devices such as tablet computers have become widely available as mainstream devices and are also used in some schools, but there is an absence of robust information regarding the efficacy of any optical/electronic low vision device or tablet computer in supporting education of young people with low vision. PURPOSE: A randomized controlled trial (RCT) is needed to measure the impact of tablet computers on education, specifically on independent access to educational material, in children and young people with low vision. We conducted a pilot RCT to determine the feasibility of conducting a full-scale trial. METHODS: This was a randomized multicenter pilot trial across two sites in the United Kingdom and one site in India. Forty children and young people aged 10 to 18 years with low vision (best-corrected visual acuity for distance between <20/60 [0.48 logMAR] and 20/400 [1.30 logMAR] in the better eye) in the United Kingdom (n = 20) and India (n = 20) were randomized to two parallel arms, with a 1:1 allocation ratio, to control (n = 20) or intervention (n = 20). Control group participants received standard low vision care. The intervention group received a tablet computer (iPad) with low vision applications and instruction in its use, including accessibility features. Four primary outcomes included (1) 6-month recruitment rate, (2) retention of participants for 3 months, (3) acceptance/usage of device, and (4) accessibility of device. RESULTS: Nineteen participants (95%) enrolled within 6 months in the United Kingdom, and 20 participants (100%), in India. Retention at 3 months was 85% (n = 17) in the United Kingdom and 95% (n = 19) in India. More than one half of participants reported using a tablet computer at school at least once every day. The majority (90%) found it easily accessible. CONCLUSIONS: This study demonstrated that it is feasible to recruit children and young people with low vision into an international multicenter RCT of electronic assistive technology. Regardless of geographical location, children and young people with low vision reported using tablet computers at least once a day at school and accessed them easily.

Tablet computers versus optical aids to support education and learning in children and young people with low vision: protocol for a pilot randomised controlled trial, CREATE (Children Reading with Electronic Assistance To Educate).

INTRODUCTION: Low vision and blindness adversely affect education and independence of children and young people. New 'assistive' technologies such as tablet computers can display text in enlarged font, read text out to the user, allow speech input and conversion into typed text, offer document and spreadsheet processing and give access to wide sources of information such as the internet. Research on these devices in low vision has been limited to case series. METHODS AND ANALYSIS: We will carry out a pilot randomised controlled trial (RCT) to assess the feasibility of a full RCT of assistive technologies for children/young people with low vision. We will recruit 40 students age 10-18 years in India and the UK, whom we will randomise 1:1 into two parallel groups. The active intervention will be Apple iPads; the control arm will be the local standard low-vision aid care. Primary outcomes will be acceptance/usage, accessibility of the device and trial feasibility measures (time to recruit children, lost to follow-up). Exploratory outcomes will be validated measures of vision-related quality of life for children/young people as well as validated measures of reading and educational outcomes. In addition, we will carry out semistructured interviews with the participants and their teachers. ETHICS AND DISSEMINATION: NRES reference 15/NS/0068; dissemination is planned via healthcare and education sector conferences and publications, as well as via patient support organisations. TRIAL REGISTRATION NUMBER: NCT02798848; IRAS ID 179658, UCL reference 15/0570.

Outcomes of Multidisciplinary Low Vision Rehabilitation in Adults.

PURPOSE: To evaluate the outcomes of multidisciplinary low vision rehabilitation (LVR) in adults with low vision (LV) in India using the Veterans Affairs Low Vision Visual Functioning Questionnaire (VA LV VFQ-48) and the Impact of Vision Impairment (IVI) questionnaire. METHODS: Consecutive adults with LV referred for the first time to the Centre for Sight Enhancement were administered the 28-item IVI and VA LV VFQ-48 before and after LVR (4 months). Rasch-scaled scores were generated for the IVI and the VA LV VFQ-48 along with each of their subscales at both the time points. Effect size (ES) was calculated using Cohen's d coefficient. RESULTS: Two hundred fifty-five patients completed the LVR program. Following LVR, the linear measures revealed significant improvements in vision-related quality of life (VRQoL) using the IVI at follow-up (P < 0.0001), with large ES for reading and accessing information (ES = 1.0) and relatively moderate ES for overall IVI (ES = 0.63) and mobility subscale (ES = 0.53). No significant improvement was found on emotional well-being subscale (ES = 0.18; P = 0.06). Similarly, significant improvements in VRQoL (P < 0.0001) were found for the VA LV VFQ-48 at follow-up, albeit moderate ES for the overall visual ability (ES = -0.67) and its subscales (reading [ES = -0.72], mobility [ES = -0.45], visual information [ES = -0.47), visual motor [ES = -0.54]). CONCLUSIONS: Regardless of the instrument used for assessment, our multidisciplinary LVR program resulted in statistically significant improvements in visual functioning and VRQoL of those adults with LV deemed appropriate for intervention (dropout rates were high); however, the improvements were modest, and the clinical relevance of these small improvements may be limited. Nonetheless, further studies should attempt to increase the completion rates in order to draw strong inferences.

Measuring Health-Related Quality of Life in Strabismus: A Modification of the Adult Strabismus-20 (AS-20) Questionnaire Using Rasch Analysis.

PURPOSE: To evaluate the psychometric properties of the Adult Strabismus-20 (AS-20)- a health-related quality of life (HRQoL) questionnaire in adults with strabismus, and if flawed, to revise the AS-20 and its subscales creating valid measurement scales. METHODS: 584 adults (meanage, 27.5 years) with strabismus were recruited from an outpatient clinic at a South Indian tertiary eye care centre and were administered the AS-20 questionnaire.The AS-20 was translated and back translated into two Indian languages. The AS-20 and its two 10-item subscales - 'psychosocial' and 'function'were assessed separately for fit to the Rasch model, including an assessment of the rating scale, unidimensionality (by principal components analysis), measurement precision by person separation reliability, PSR, targeting, and differential item functioning (DIF; notable > 1.0 logits). RESULTS: Response categories were not used as intended, thereby, required re-organization and reducing their number from 5 to 3. The AS-20 had adequate measurement precision (PSR = 0.87) but lacked unidimensionality; however, deletion of the six multi-dimensionality causing items and an additional three misfitting items resulted in 11-item unidimensional questionnaire (AS-11). Two items failed to satisfy the model expectations in the 'psychosocial' subscale and were deleted - resulting in an 8-item unidimensional scale with adequate PSR (0.81) and targeting (0.23 logits). One item misfit in the 'function' subscale and was deleted-resulting in a 9 item Rasch-revised unidimensional subscale with acceptable PSR (0.80) and targeting (0.97 logits).None of the items displayed notable DIF by age, gender and level of education. CONCLUSIONS: The AS-11 and its two Rasch-revised subscales - 8-item psychosocial and 9-item function subscale may be more appropriate than the original AS-20 and its two 10-item subscales for use as unidimensional measures of HRQoL in adults with strabismus in India. Further work is required to establish the validity of the revised rating scale.

Assessing the effectiveness of low vision rehabilitation in children: an observational study.

PURPOSE: To evaluate the change in visual functioning (VF) using the L. V. Prasad-Functional Vision Questionnaire II (LVP-FVQ II) following multidisciplinary low vision rehabilitation (LVR) services in children with low vision (LV). METHODS: Children with LV referred for the first time to the Centre for Sight Enhancement were administered the LVP-FVQ II at baseline and at 3 to 4 months' follow-up to assess the outcomes of LVR. Participants' responses to the LVP-FVQ II at baseline and follow-up were transformed into interval-level estimates of VF using Rasch analysis. Cohen's d values (effect size) were used to estimate the magnitude of change in VF. RESULTS: A total of 183 participants completed the rehabilitation (mean age, 11.9 years; male, 57%). More than one-half of the participants had retinal disorders (55%) and most were moderately visually impaired (<20/60-20/200, 76.5%). Using the LVP-FVQ II, significant improvement in VF after rehabilitation was recorded (P < 0.0001) and the increase in VF (SD) was 1.20 (1.82) logits. Using Cohen's d, the magnitude of the improvement in LVR intervention at follow-up was found to be 0.75, indicating nearly large treatment effect. CONCLUSIONS: Ours is the first study to provide strong evidence that LVR services result in nearly large and significant improvements in the overall VF in children with LV, regardless of the cause of LV. These results should encourage eye care professionals to refer children with LV to LVR services. Further investigation is needed to determine if the improvement in VF can be sustained over a longer duration (>4 months).

Measuring coping in parents of children with disabilities: a rasch model approach.

BACKGROUND: Parents of a child with disability must cope with greater demands than those living with a healthy child. Coping refers to a person's cognitive or behavioral efforts to manage the demands of a stressful situation. The Coping Health Inventory for Parents (CHIP) is a well-recognized measure of coping among parents of chronically ill children and assesses different coping patterns using its three subscales. The purpose of this study was to provide further insights into the psychometric properties of the CHIP subscales in a sample of parents of children with disabilities. METHODS: In this cross-sectional study, 220 parents (mean age, 33.4 years; 85% mothers) caring for a child with disability enrolled in special schools as well as in mainstream schools completed the 45-item CHIP. Rasch analysis was applied to the CHIP data and the psychometric performance of each of the three subscales was tested. Subscale revision was performed in the context of Rasch analysis statistics. RESULTS: Response categories were not used as intended, necessitating combining categories, thereby reducing the number from 4 to 3. The subscale - 'maintaining social support' satisfied all the Rasch model expectations. Four item misfit the Rasch model in the subscale -maintaining family integration', but their deletion resulted in a 15-item scale with items that fit the Rasch model well. The remaining subscale - 'understanding the healthcare situation' lacked adequate measurement precision (<2.0 logits). CONCLUSIONS: The current Rasch analyses add to the evidence of measurement properties of the CHIP and show that the two of its subscales (one original and the other revised) have good psychometric properties and work well to measure coping patterns in parents of children with disabilities. However the third subscale is limited by its inadequate measurement precision and requires more items.

Quality of life of caregivers of children with congenital glaucoma: development and validation of a novel questionnaire (CarCGQoL).

PURPOSE: We developed and validated an instrument to measure the quality of life (QoL) of caregivers of children with primary congenital glaucoma (PCG): the Caregiver's Congenital Glaucoma Quality of Life (CarCGQoL) questionnaire. METHODS: A total of 70 caregivers of children with PCG under follow-up at a tertiary eye care center in India participated in a series of focus groups, and pre- and pilot testing phases in the development of the 45-item CarCGQoL questionnaire. Subsequently, this instrument was administered to 111 caregivers of children with PCG awaiting glaucoma surgery. Response to each item was rated on a four-category scale. Rasch analysis was used to validate the instrument's psychometric properties, such as unidimensionality (by principal components analysis [PCA] of residuals), item fit to model, measurement precision (by person separation [PS]), response category performance, differential item functioning (DIF), and targeting of items to participant's QoL. RESULTS: Categories required reorganization resulting in a shortened rating scale of 3 categories. The instrument showed misfit to the Rasch model and lacked unidimensionality. Deleting 15 items (obtained through PCA of residuals) restored unidimensionality, but additional items misfit, necessitating item reduction. In addition, 2 items showed DIF and were deleted. Finally, a 20-item CarCGQoL instrument showed good fit and unidimensionality. Targeting was good (0.69 logits) and PS was 2.51, indicating good measurement precision. CONCLUSIONS: We have developed a psychometrically robust 20-item caregiver derived questionnaire, the CarCGQoL, that is a valid and reliable measure of QoL of caregivers of children with PCG. Given its brevity, it is quick and easy to administer in the clinic, and has potential for use as an outcome measure in clinical trials of treatment of PCG.

The patient health questionnaire-9: validation among patients with glaucoma.

BACKGROUND: Depression and anxiety are two common normal responses to a chronic disease such as glaucoma. This study analysed the measurement properties of the depression screening instrument - Patient Health Questionnaire-9 (PHQ-9) using Rasch analysis to determine if it can be used as a measure. METHODS: In this hospital-based cross-sectional study, the PHQ-9 was administered to primary glaucoma adults attending a glaucoma clinic of a tertiary eye care centre, South India. All patients underwent a comprehensive clinical evaluation. Patient demographics and sub-type of glaucoma were abstracted from the medical record. Rasch analysis was used to investigate the following properties of the PHQ-9: behaviour of the response categories, measurement precision (assessed using person separation reliability, PSR; minimum recommended value 0.80), unidimensionality (assessed using item fit [0.7-1.3] and principal components analysis of residuals), and targeting. RESULTS: 198 patients (mean age ± standard deviation  = 59.83±12.34 years; 67% male) were included. The native PHQ-9 did not fit the Rasch model. The response categories showed disordered thresholds which became ordered after category reorganization. Measurement precision was below acceptable limits (0.62) and targeting was sub-optimal (-1.27 logits). Four items misfit that were deleted iteratively following which a set of five items fit the Rasch model. However measurement precision failed to improve and targeting worsened further (-1.62 logits). CONCLUSIONS: The PHQ-9, in its present form, provides suboptimal assessment of depression in patients with glaucoma in India. Therefore, there is a need to develop a new depression instrument for our glaucoma population. A superior strategy would be to use the item bank for depression but this will also need to be validated in glaucoma patients before deciding its utility.

Is utility-based quality of life in adults affected by glaucoma?

PURPOSE: We evaluated the utility values (UVs), using the time trade off (TTO) technique, associated with primary glaucoma and varying degrees of visual field (VF) loss. METHODS: In this cross-sectional study, 198 adults (mean age, 59.8 years) with primary glaucoma were recruited from the glaucoma clinic of a tertiary center in Hyderabad, South India. Each patient underwent comprehensive glaucoma evaluation, and completed the utility (TTO) and Glaucoma Quality of Life-15 questionnaires (Rasch version, Glaucoma Activity Limitation [GAL]-10). Better mean deviation (MD, using Humphrey Field Analyzer program 24-2) between two eyes was used to classify participants into mild, moderate, and severe VF loss groups. Utilities (range, 0.0-1.0) derived by TTO technique (lifetime traded against perfect vision) and interval level Rasch scores of GAL-10 were used for analyses. RESULTS: Mean UV was 0.81 (95% confidence interval [CI], 0.78-0.84); that is, a decrease in quality of life (QoL) of 19%. Of the subjects, 59% were willing to trade lifetime in return of perfect vision; those willing to trade were significantly younger with poorer acuity in the worse-seeing eye. In univariate and multivariate analysis, severe VF loss in the worse eye was associated with lower UV (ß = -0.108; 95% CI, -0.201 to -0.014; P = 0.02). CONCLUSIONS: Our results show that primary glaucoma in adults causes substantial decrease in UVs (and QoL thereof), and is highly dependent on the severity of VF loss in the worse eye.

Revised Olweus Bully/Victim Questionnaire: evaluation in visually impaired.

PURPOSE: To explore the psychometric properties of the revised Olweus Bully/Victim Questionnaire (OBVQ) in children with visual impairment (VI) using Rasch analysis. METHODS: One hundred fifty Indian children with VI between 8 and 16 years (mean age, 11.6 years; 69% male; mean acuity in the better eye of 0.80 logMAR [Snellen, 20/126]) were administered the revised OBVQ. The 40-item revised OBVQ was developed to assess victimization (i.e., being bullied) and bullying (bullying others) in normally sighted schoolchildren. Only 16 items are used for Rasch analysis and are divided into two parts: I (victimization, eight items) and II (bullying others, eight items). Separate Rasch analysis was conducted for both parts, and the psychometric properties investigated included behavior of rating scale, extent to which the items measured a single construct (unidimensionality by fit statistics and principal component analysis [PCA] of residuals); ability to discriminate among participants' victimization and bullying behaviors (measurement precision as assessed by person separation reliability [PSR] minimum recommended value, 0.80); and targeting of items to participants' victimization and bullying. RESULTS: Response categories were misused for both parts I and II, which required repair before further analysis. Measurement precision was inadequate for both parts (PSR, 0.64 for part I and 0.19 for part II), indicating poor discriminatory ability. All items fit the Rasch model well in part I, indicating unidimensionality that was further confirmed using PCA of residuals. However, an item misfit in part II that required deletion following which the remaining items fit and PCA of residuals also supported unidimensionality. Targeting was -0.58 logits for part I, indicating that the items were matched well with the participants' victimization. By comparison, targeting was suboptimal for part II (-1.97 logits). CONCLUSIONS: In its current state, the revised OBVQ is not a valid psychometric instrument to assess victimization and bullying among children with VI.

Assessment of the impact of keratoconus on vision-related quality of life.

PURPOSE: We determined if the Impact of Vision Impairment (IVI) is a valid questionnaire to measure the vision-related quality of life (VRQoL) in keratoconus patients, and investigated if the VRQoL varied with disease severity in this sample. METHODS: WE RECRUITED 160 CONSECUTIVE BILATERAL KERATOCONUS PATIENTS (MEAN AGE 23.3 YEARS, 63% MALE) FROM AN INDIAN TERTIARY EYE CARE CENTER. PARTICIPANTS UNDERWENT A CLINICAL EXAMINATION AND COMPLETED THE IVI. PARTICIPANTS WERE DIVIDED INTO THREE GROUPS BASED ON THE AVERAGE OF THE STEEP KERATOMETRY (K) READINGS: mild (average Sim K < 45 diopters [D]), moderate (average Sim K 45-52 D), and severe (average Sim K > 52 D). Rasch analysis was used to validate the IVI and the VRQoL scores thus obtained were compared across the disease groups. RESULTS: THE MAJORITY (63%) OF PATIENTS HAD SEVERE, WHILE THE REMAINDER (37%) HAD MODERATE KERATOCONUS. RASCH ANALYSIS DEMONSTRATED THE VALIDITY OF THE IVI TO ASSESS VRQOL THROUGH TWO SUBSCALES: vision-specific functioning (VF) and emotional well-being (EWB). There was no significant difference in VF (mean change -0.16, P = 0.55) and EWB scores (mean change -0.32, P = 0.23) between moderate and severe keratoconus groups. CONCLUSIONS: The revised IVI subscales have interval-level measurement properties, which support their suitability to measure VRQoL in this keratoconus sample. Patients with moderate or severe keratoconus had similar, but higher VRQoL scores as assessed by the revised IVI subscales, indicating lack of impact of the disease on their VRQoL. However, this does not exclude the possibility of finding an impact in other populations.

The second version of the L. V. Prasad-functional vision questionnaire.

PURPOSE: The L. V. Prasad-Functional Vision Questionnaire (LVP-FVQ) was developed using Rasch analysis to assess self-reported difficulties in performing daily tasks in school children with visual impairment (VI) in India. However, the LVP-FVQ has psychometric problems of inadequate measurement precision and lack of detailed assessment of dimensionality. Furthermore, items pertaining to use of technology are lacking. The aim of this study was to present the development and validation of the second version of LVP-FVQ (LVP-FVQ II). METHODS: Development of LVP-FVQ II involved extracting items from other similar questionnaires (albeit developed for Western populations) and focus group discussions of children with VI and their parents that resulted in a 32-item pilot questionnaire. Overall, six items from the LVP-FVQ were retained. The questionnaire underwent pilot testing in 25 such children, following which a 27-item LVP-FVQ II emerged, and this was administered to 150 children with VI. Response to each item was rated on a three-category scale. Rasch analysis was used to validate the LVP-FVQ II. RESULTS: Rating scale was used by participants as was intended to. Four mobility-related items required deletion, as these did not contribute toward measurement of a single construct, indicating a secondary dimension. Deletion of the four items resulted in the 23-item unidimensional LVP-FVQ II, with good measurement precision, effective targeting of item difficulty to participant ability, and lack of notable differential item functioning. The LVP-FVQ II has high reliability, indicating that it is effectively able to discriminate between visual disability of school children in India, and is valid across age, gender, duration of VI, and location of residence. CONCLUSIONS: Given the superior measurement properties and the interval-level scores, the LVP-FVQ II appears to offer advantages over LVP-FVQ in assessment of difficulties in performing daily tasks in this population. It can be adapted for use in other developing countries.

Impact of glaucoma on visual functioning in Indians.

PURPOSE: To evaluate the impact of glaucoma on visual functioning in Indians. METHODS: Patients attending the glaucoma service who had undergone a comprehensive glaucoma evaluation were recruited. Better mean deviation (MD, using Humphrey Field Analyzer program 24-2) between two eyes was used to classify participants into mild, moderate, and severe visual field (VF) loss groups. Participants were administered the Glaucoma Quality of Life-15 (GQL-15) questionnaire. Rasch analysis was used to validate the GQL-15 and its four subscales. Linear regression was used to determine associations between GQL-15 scores and VF loss after adjusting for sociodemographic variables. RESULTS: A total of 198 patients (mean age ± SD, 59.8 ± 12.3 years; 67% male) were recruited. Participants with severe VF loss (39%) followed by mild loss (35%) comprised the largest group. Rasch analysis resulted in a 10-item reliable and valid questionnaire: the Glaucoma Activity Limitation-10 (GAL-10). Although a single subscale, "peripheral vision," met requirements of the Rasch model, it could not be preserved in the GAL-10. In multivariate analyses, the middle-income group (compared with higher income) and severe VF-loss (compared with mild VF-loss) participants reported significantly poorer functioning on GAL-10 ([ß = 0.84; 95% confidence interval (CI), 0.16-1.52; P = 0.02] and [ß = 1.19; 95% CI, 0.61-1.78; P < 0.000], respectively). None of these associations were, however, clinically significant. CONCLUSIONS: Glaucoma patients in India, especially those with severe VF loss, face significant challenges in performing daily tasks and in mobility. It is important to prevent progression such that activity limitation is minimized in glaucoma patients.

National Eye Institute Visual Function Questionnaire or Indian Vision Function Questionnaire for visually impaired: a conundrum.

PURPOSE: Both the long form visual functioning scale (LFVFS(39)) and visual functioning scale (VFS) are measures of visual functioning (VF) that represent the Rasch-scaled versions of the NEI-VFQ(39) and the Indian vision function questionnaire (IND-VFQ), respectively. The objectives of this study were to investigate if the 15-item LFVFS(39) and 13-item VFS of the IND-VFQ meet the assumptions of the Rasch model and measure the same construct, VF, in an Indian visually impaired (VI) population. METHODS: Data from 120 VI adults administered both instruments concurrently, were fitted to the Rasch measurement model to demonstrate that each instrument satisfies the assumptions of the model (including unidimensionality by principal components analysis); and both instruments can be cocalibrated onto a single underlying continuum of VF. RESULTS: Both instruments required category reorganization for optimal rating scale functioning and possessed similar measurement precision (person separation = 2.76). Separate analysis of each instrument (eigenvalues, 2.3 and 1.9 for LFVFS(39) and VFS of IND-VFQ, respectively) and the pooled 28-item analyses (eigenvalue, 2.8) satisfied the assumptions of the Rasch model, including unidimensionality. Furthermore, all items fit in the separate and pooled analyses. Separate item and person measures for each instrument correlated strongly with estimates from the pooled data (r > 0.9 for all, P < 0.0001). CONCLUSIONS; Both the LFVFS(39) and VFS of the IND-VFQ measure the same construct, VF, and with equal measurement precision in an Indian VI population. Both instruments can be calibrated onto a single metric, thereby, enabling a comparison of their measurement range of VF.