Development and validation of an Arabic version of the Visual Functioning Index VF-14 for cataract patients.

PURPOSE: To develop and validate an Arabic version of the Visual Functioning Index (VF-14) for patients with cataracts.
MATERIALS AND METHODS: The VF-14 was translated into Arabic by an epidemiologist and an ophthalmologist, both fluent in Arabic and English. The VF-14 was administered to patients diagnosed with cataract at two hospitals in Egypt and two hospitals in Saudi Arabia. Patients were also administered three other forms; the cataract symptoms score (CSS); global measure of vision; and cataract medical form. Internal reliability and external validity were measured. Index sensitivity to visual acuity was detected and potential effective factors were investigated. Correlation analyses were performed. A p value less than 0.05 was considered statistically significant.
RESULTS: The translated VF-14 was consistent and reliable (σ = 0.763, p < 0.0001). It was also statistically significantly sensitive to vision (p < 0.0001). The mean calculated index was 62.18 ± 19.34, and was highly correlated with; CSS and other scores (p < 0.0001, all cases). Factors that may affect the index are; age, sex, vision, wearing glasses, type, position, and severity of cataract.
CONCLUSION: The Arabic VF 14 is a reliable and valid tool for evaluation of both visual functioning and quality of visual life among cataract patients. It is also sensitive to changes in visual acuity, demographic, and clinical characteristics.

INTRODUCTION

Cataract is the major cause of low vision and blindness in the Middle East (45.2%) and worldwide (50%).12 In the Middle Eastern region, 31.4 million individuals aged 60 years or older and 20.8 million below 60 years of age are visually disabled due to cataract.3 As the volume of cataract surgery increases due to the aging population, there is a need to continually monitor and evaluate surgical outcomes and the impact on visual function and quality of life. The Visual Functioning Index VF-14 was developed and validated by Steinberg and colleagues in the early nineties.4 The rationale for developing this index was the need for a tool that can accurately measure cataract surgery outcomes as visual acuity alone was considered as an insufficient measure.56 Since its introduction, the VF-14 has been widely accepted and utilized for various ocular diseases that can affect vision including estimation of the need and urgency of cataract surgery. The VF-14 has been used to evaluate and compare different surgical procedures. This index has been used for glaucoma, retina, cornea, keratoplasty, macular degeneration, low vision, and prevention of blindness research.7–11

The VF-14 was originally developed in English for developed countries, consequently, there was a debate regarding its global validity. Therefore, various investigators have translated, modified and validated the VF-14 to suit different languages and settings. The VF-14 has proved to be reliable, valid, and highly consistent when used for different purposes, in different languages and settings.

In 1999, Karin van Dijk and colleagues (1999) validated a modified version for African countries where a lot of research to prevent blindness – specifically from cataract – takes place.12 In the Middle East, Arabic is spoken in 22 Arabic countries with a total population of 291 million inhabitants. Additionally, the prevalence of blindness in this region is one of the highest.13 There is also a dramatic increase in ocular research that mandates the need to develop and validate a reliable Arabic version of the VF-14. Therefore, we sought to translate, adapt, and validate an Arabic version of the VF-14 for subsequent use in ophthalmologic research.

MATERIALS AND METHODS

The current study was conducted in a cross sectional study design. The original VF-14 questionnaire was separately translated into Arabic by two different ocular researchers (an epidemiologist from Egypt and an ophthalmologist from Saudi Arabia who were fluent in both Arabic and English). Subsequently the two versions were matched and unified. The new Arabic questionnaire was translated back to English by a third researcher (ophthalmologist) and then matched to the original version by an optometrist whose native language was English. Minimal modifications were required by the research team to formulate a final version of the Arabic VF-14 questionnaire to suit the Arabic culture.

Three other forms were administered in parallel with the VF-14 form including the Cataract Symptoms Score (CSS), Global Measure of Vision (including; Trouble and Satisfaction with current vision forms), and a cataract medical form which collected information on patient demographics, visual acuity, and grade, type, and position of cataract. Cataract categorization and grading were simplified and standardized using international guidelines.14–16 Meanwhile, patient visual acuity classification followed the World Health Organization (WHO) standardized guideline.1718

Scoring and scaling system

Each of the VF-14 questions was given a score ranging from 0 – 4 as follows; 4; “no difficulty”, 3; “a little difficulty”, 2; “moderate difficulty”, 1; “a great deal of difficulty” and 0; “Unable to do the activity” while “not applicable” was left blank and excluded from the analysis. The scores were added for all questions and the total was divided by the total number of answered questions. The total score was then multiplied by 4 to get the overall index for each person which indicated the patient's visual functioning scale ranging from (0 – 100) where 0 meant unable to do all applicable activities, and 100 means best possible visual functioning. Likewise, the global measure of vision index (trouble and satisfaction with current vision) were scored in terms of trouble as; 0; “None”, 1; “A little”, 2; “A moderate amount”, 3; “A great deal” and in terms of satisfaction as; 3; “Very dissatisfied”, 2; “Moderately dissatisfied”, 1; “Satisfied”, and 0; “Very satisfied”. The CSS was calculated as; 3; “Very bothered”, 2; “Somewhat bothered”, 1; “A little bothered” and 0; “Not at all bothered”. Calculations of the overall index were performed through summing the total results in a cataract symptoms index for each patient ranging from 0 (no symptoms or not bothered by any of the symptoms) to 15 (very bothered by all five symptoms).

Implementation of the index

The integrated package of forms was administered to a total of 1413 cataract patients from two hospitals in Egypt and two others in Saudi Arabia. Patients recruited for the study were scheduled for surgery within 3 months (maximum). Inclusion criteria were; Arabic as a native language, age of 20 years or older, no prior ocular surgery, no combined procedures, in addition to absence of any ocular co-morbidities.

Statistical analysis and validation

Data management/verification processes were conducted and all ineligible data were removed due to; missing, incomplete, facing contradictions, and or inconsistencies. Validation process included three phases; (1) scoring and descriptive analysis, (2) internal consistency testing (reliability) using Cronbach's α test, (3) testing validity by evaluating correlation between the VF-14 score and; the logarithm of the minimum angle of resolution (LogMAR) visual acuity, CSS, Visual Trouble Score, and Visual Satisfaction Score using Pearson's correlation coefficient. One way analysis of variance (ANOVA) was performed to investigate the sensitivity of the VF-14 to different levels of visual acuity while multiple linear regression was conducted to investigate different factors affecting the new index. A p value less than 0.05 was considered statistically significant. The unit of analysis was the person (not eye) where; visual acuity and the corresponding group of vision were calculated as an average of (0.25* the worse eye + 0.75* the best eye).

Ethics approval was obtained from the Institutional Research and Ethics Board (IREB) of King Saud University (IREB-09-702) and the study conformed to the tenets of the Declaration of Helsinki.

RESULTS

The index was administered to patients booked for cataract surgery from March 1st to September 30th 2010 who met the inclusion criteria. During data management, 33 cases were excluded leaving a total of 1380 patients. The study cohort was recruited from the following institutions; 324 (23.5%) patients from King Abdul Aziz University Hospital, Riyadh; 186 (13.5%) patients from King Fahd Hospital, Baha; 522 (37.8%) patients from Magrabi Eye Hospital, Cairo and; 348 (25.2%) patients from Magrabi Eye Center, Tanta. The first two hospitals were based in two different governorates in Saudi Arabia and the other two hospitals were based in two different governorates in Egypt.

The mean age (±SD) was 63.41 ± 11.19 years (range, 24 years to 80 years). There were 840 (60.9%) males and 540 (39.1%) females. The majority (840; 60.9%) of patients were undergoing surgery on the left eye and 720 (52.2%) patients had visual acuity <20/40. Ninety (6.5%) patients were wearing spectacles. Most (690; 50%) of the patients presented with severe cataract, and posterior sub-capsular cataract was present in 930 (67.4%) patients [Table 1].

Table 1

Distribution of cases per type and position of cataract at presentation

The mean score for the VF-14 was 62.18 ± 19.34 (range, 15.38 to 88.89) [Table 2]. Data on demographics, visual acuity, IOL power and mean score of the visual function index are presented in Table 2. Cronbach's α test for intra-class correlation indicated that the index was statistically significantly reliable (Cronbach's α; 0.763, 95% confidence intervals (CI): [0.743 – 0.782]; p < 0.0001).

Table 2

Demographics and mean score of visual functioning questionnaires and visual acuity

The VF index had statistically significant inverse correlations with the Cataract Symptom Score, Trouble Index, Dissatisfaction Index, and the overall LogMAR Visual Acuity (Pearson ρ:–0.76, –0.63, –0.73, –0.77 respectively; p < 0.0001 for all correlation tests).

The index showed a high correspondence to the level of vision as clearly demonstrated in Table 3. The VF score gradually decreased with decreasing visual acuity [Figure 1]. There was a statistically significant difference in the mean VF-14 score among the – WHO standard – groups of visual acuity (Normal, Low vision, Severe low vision, and Blindness) (ANOVA F; 714.52, p < 0.0001). Post hoc analysis using Tukey's test indicated that the source of variation was in all alternatively tested groups except for the low vision and normal groups [Table 4].

Table 3

Average visual function score per different groups of Visual Acuity

Figure 1

Pattern of visual functioning index (VF 14) with different levels of visual acuity

Table 4

Matrix of Binary Differences between Groups (Post Hoc analysis)

Multiple regression analysis indicated that factors affecting the VF index were; Age, Sex, Vision Group, Spectacle wear, Type, and Position of cataract and Severity of Cataract Symptoms. All factors were highly statistically significant (p < 0.0001, all cases) except for Sex (p = 0.001), and Sclerotic position of cataract (p = 0.032).

DISCUSSION

The need for translation and validation of quality of life indices into local languages has been extensively addressed by the literature. The VF-14 was translated and validated into French, Italian, Spanish, Turkish, Brazilian, Chinese, and several other languages. The VF-14 index was found to have good validity after translation and validation into different languages with minimal adaptation to each language. The rationale for this localization is to adjust for the cultural and other community specific differences. Additionally, there were many attempts to develop similar indices for different age groups.1920 However, the VF-14 showed convenient flexibility either to minimal modifications, reproducibility,21 or to shortening of its questions where it persisted to be reliable and valid.22 Despite the availability of similar indices such as the National Eye Institute NEI VFQ 25, or the WHO VF 20, the VF-14 – which was developed as cataract specific – was then widely utilized for evaluation of other ocular interventions including long term follow up.23 Furthermore, the VF-14 proved to be a reliable tool for decision making24 and prioritization of waiting lists in cataract surgeries.

In an effort to cope with the tremendous increase in ocular research in many Arabic speaking countries, we translated and minimally modified the VF-14 for use in Arabic speaking countries and communities. The new index showed highly significant reliability and validity and was comparable to classic outcome assessment indices including; LogMAR visual acuity, dissatisfaction, and trouble with vision indices (global measures of vision). The CSS is widely accepted as a reliable, valid, and very sensitive tool to assess cataract patients preoperatively. It is internationally recognized as a highly correlated index to the VF-14.2526 Our results are consistent with this international trend. Hence, using the Arabic version would enable international comparisons in addition to standardization of quality eye care. The sensitivity of the Arabic VF-14 to change in vision is similar to the findings of Steinberg and co-workers4 and the general trend to other translation and validation studies.2526 This provides additional evidence on the reliability and validity of the VF-14 as a tool for measuring visual functioning for cataract patients. Additional studies are required to assess the effectiveness of the Arabic VF-14 in other ocular diseases and to use it as a tool for evaluation and comparison of different procedures.

CONCLUSION

The findings of this study indicate that the Arabic VF-14 is a reliable and valid tool for evaluation of both visual functioning and quality of visual life among cataract patients preoperatively. The new Arabic tool can be affected by age, sex, spectacle wear, in addition to different levels of vision and the maturity, severity, type, and position of cataract. The Arabic VF-14 is highly recommended for evaluating visual function as an outcome indicator of surgical intervention either in cataract or in other ocular diseases after pre-testing. It can also be used in decision making process for surgical interventions and for prioritization of surgical waiting lists.