Cross-sectional study of prevalence, causes and trends in visual impairment in Nirmal District, Telangana, India: Nirmal Eye Evaluation for Trends study

Objective To determine the prevalence, causes and risk factors associated with visual impairment (VI) in the Nirmal district of Telangana, India, using extended Rapid Assessment of Visual Impairment (RAVI) methodology. Design Cross-sectional study. Setting Community setting. Participants Participants aged ≥16 years were enumerated from 90 randomly selected clusters and 4629/5400 (85.7%) participants were examined. Presenting visual acuity (VA) was assessed using a Snellen chart with E optotypes at a 6 m distance. Near vision was assessed binocularly using an N notation chart with tumbling E optotypes at a 40 cm distance. An anterior segment examination done followed by distance direct ophthalmoscopy at 50 cm. Non-mydriatic fundus images were obtained. VI was defined as presenting VA worse than 6/12 in the better eye. The prevalence of VI in the current study was compared with a RAVI study conducted in 2014 to assess the trends in VI among those aged ≥40 years. Primary outcome Prevalence, causes and risk factors for VI. Results Among those examined, 55% were women, 53% had at least school-level education, 2.3% self-reported diabetes and 8.7% self-reported hypertension. The prevalence of VI was 8.81% (95% CI 8.01% to 9.67%). Overall, uncorrected refractive errors (49.5%) were the leading cause of VI, followed by cataracts (40.2%) and posterior segment diseases (4.9%). Among those aged ≥40 years, the prevalence of VI declined by 19.3% compared with the 2014 baseline study (from 20.2% to 16.3%; p<0.01). Conclusion The extended RAVI study conducted in the Nirmal district showed a considerable decline in the prevalence of VI. Targeted interventions are needed to provide adequate eye care for the high-risk groups in this district.


INTRODUCTION
Over a billion people suffer due vision impairment (VI) globally, with cataracts and uncorrected refractive errors (URE) being the leading causes. 1 2 Both these conditions can be addressed using cost-effective interventions, such as spectacles and cataract surgery.
Population-based data on the prevalence and causes of VI are essential to plan eye care service delivery models to address this global problem.Though conventional epidemiological studies provide the data, they are often resource-intensive and need expertise to implement them.The rapid assessment methods are low-cost epidemiological tools that provide data on the prevalence and causes of VI using limited resources while being relatively easy to implement.In addition, these rapid assessments can be repeated at stipulated intervals to study the temporal trends in a given region. 3Rapid assessment studies are even more important now, with WHO setting global targets for effective cataract surgical coverage and effective refractive error coverage as indicators to measure the progress towards universal eye health. 4apid assessment studies initially focused on cataract alone; however, they were modified and evolved to cover other causes of VI, with an increasing focus on emerging eye conditions, such as diabetic retinopathy and refractive errors. 3 5Rapid Assessment of Visual Impairment (RAVI) is the offshoot of multiple rapid assessment methods developed and has been used extensively in India

STRENGTHS AND LIMITATIONS OF THIS STUDY
⇒ Rapid assessments typically focus on participants aged ≥40 years.This study extends the rapid assessment methodology to include younger age groups (≥16 to 39 years) and provides estimates on the prevalence and causes of visual impairment (VI).⇒ In addition to prevalence estimates, temporal trends in the prevalence of VI are presented.⇒ As a randomly selected population-based sample was used, the results from the study can be extrapolated to the population in the region.⇒ The over-representation of women could have overestimated the prevalence of VI in our study.
Recently, it has been modified to include younger individuals (≥16 years) and has been renamed as the extended RAVI methodology. 12In addition, new tools have been added to collect data on systemic conditions and disabilities, helping to more holistic planning of eye health programmes. 5 13The Nirmal Eye Evaluation for Trends is the first study to use extended RAVI.In this study, we report the prevalence, causes and risk factors of VI in the Nirmal district and adjoining areas of Telangana, India.In addition, this paper also compares the temporal trends in the prevalence of VI in this region using data from a previous study conducted in 2014. 14

MATERIALS AND METHODS Patient and public involvement
Patients and other members of the public were not involved in the design of the study.

Sampling strategy
Assuming a VI (presenting visual acuity (VA) worse than 6/12) prevalence of 3.5%, allowing for a 95% CI, a precision of 20%, a design effect of 1.6 for a predetermined cluster size of 60 participants and a 20% non-response rate, the minimum sample size required was 5270, which was rounded up to 5400 participants (90 clusters).A multistage cluster random sampling procedure with a compact segment sampling method was used, which has been described in previous reports. 14The study area had a population of 0.5 million people and comprised 10 subdistricts (mandal) from the Nirmal (8) and Nizamabad (2) districts.The eye care needs of the study area were serviced by a secondary centre of L V Prasad Eye Institute.Data were collected between November 2021 and March 2022.

Data collection
Three teams, each comprising a vision technician and two community eye health workers, collected the data.They were supervised by a study coordinator (optometrist), who was also responsible for travel logistics and quality control.The examiners were trained to conduct the study procedures and document the findings.A reliability assessment was conducted before the study to assess the interobserver agreement on VA with a gold-standard senior optometrist.All examiners had a good agreement with the gold-standard optometrist (kappa 0.8 or more).
One of the three study teams visited participants at their homes and conducted eye examinations.The time of the visits was planned to maximise the availability of the participants at their households for examination.In each selected household, all the individuals who fulfilled the age criteria were documented, and all those who were available during the visit were examined.At least two attempts were made to examine those who were unavailable during the first visit, after which they were marked as unavailable.

Eye examination protocol
A brief interview was conducted to collect personal and sociodemographic information, such as age, education level and systemic health conditions (online supplemental file 1).Data related to the ocular history, including current and previous use of spectacles, use of eye-drops and details of any previous surgery, were also collected.Information regarding the barriers to the uptake of eye care services was also collected using a structured questionnaire.
6][17] In brief, the distance visual acuity (VA) was assessed using a standard Snellen chart with tumbling E optotypes at a distance of 6 m.If a participant was unable to identify the letters in the first line of the chart, the distance between the participant and the chart was progressively reduced to 3 m and then 1 m till VA could be recorded.Unaided VA was recorded for all participants.Aided VA was recorded for participants using spectacles for correction.Aided VA was considered as the presenting VA (PVA) for those with spectacles, and an unaided VA was considered as the PVA for those without spectacles.If the PVA was worse than 6/12, the VA was recorded using a multiple pinhole occluder.Near vision was assessed binocularly using the N notation near vision chart at a fixed distance of 40 cm in ambient lighting conditions.The fixed distance was maintained using a string attached to the near vision chart.Both unaided and aided near vision were assessed if the participant reported spectacles use for near.Near vision was reassessed using near addition lenses in a trial frame appropriate for that age among participants with near vision worse than N6.
An eye examination was performed using a torchlight/ portable handheld slit lamp (Keeler PSL Classic, USA).The lens was assessed using distant direct ophthalmoscopy at approximately 50 cm distance in a shaded area (indoors), which was graded as normal, obvious lens opacity, aphakia, pseudophakia without posterior capsular opacification (PCO) or pseudophakia with PCO.If the lens could not be examined because of corneal opacities, phthisis bulbi or absent globe, then it was documented in the data form.A non-mydriatic portable fundus camera (Visuscout 100 Handheld Fundus Camera, Carl Zeiss Meditec, USA) was used to capture retinal images.Two images, one optic disc-centred and another maculacentred, were captured for each eye.All the images were evaluated by experienced graders at L V Prasad Eye Institute.The participants with VI and those requiring other eye care services were referred to the nearest eye care facility for management.
The WHO categorises visual impairment (VI) into four categories based on the presenting VA in the better eye. 18he four categories are as follows: mild VI (MiVI-VA worse than 6/12-6/18), moderate VI (MVI-VA worse Open access than 6/18-6/60), severe (SVI-worse than 6/60-3/60) and blindness (VA worse than 3/60 to no perception of light).The case definitions for the causes of VI used in this study have been described in our previous publications. 11In brief, URE was defined as presenting VA<6/12, improving to 6/12 or better with pinhole.Cataract was defined as an opacity of the crystalline lens as seen with torchlight and obscuring the red reflex, partially or completely, on the distance direct ophthalmoscopy, resulting in a VA<6/12 that does not improve with pinhole.Posterior segment disease was considered as the cause of VI in cases where there was no media opacity and VA did not improve with a pinhole.Posterior Capsular Opacification (PCO), phthisis bulbi/absent globle and corneal opacities/oedema after cataract surgery were marked as surgical complications.After the eye examination, the principal cause of VI was recorded for each eye separately, and then for the person.If there was more than one cause, the cause that was more easily treatable or correctable was marked as the main cause of VI.
As this study was conducted during the pandemic, all COVID-19-related protocols were followed, including the use of masks (N-95) and visors at all times, frequent hand sanitisation and social distancing.All the team members were vaccinated before the start of the study.The equipment used, such as trial frames and multiple pinhole occluders, were disinfected with alcohol wipes/swabs after each use.The participants were offered hand sanitiser to clean their hands before starting the study procedures.The current health status of all the participants was enquired before the eye examinations.

Data management
In the field, data were collected using paper forms.The forms were then transported to the data centre for entry into a Microsoft Access database.Data analyses were performed using the Stata Statistical Software for Windows, V.14 (StataCorp).The prevalence estimates were adjusted to the age and gender distribution of the population for the year 2011 and presented with the 95% CIs.The demographic associations of VI with age, gender, education and systemic conditions were assessed using multiple logistic regression models and adjusted ORs with 95% CI are reported.A study using the conventional RAVI methodology (included individuals aged 40 years and older) was conducted in the same region in 2014. 14he prevalence estimates from the current study were compared with the 2014 study to assess the trends in VI over time in this region.

Causes of VI
Overall, UREs (49.5%) were the leading cause of VI, followed by cataract (40.2%) and posterior segment diseases (4.9%).UREs were the leading cause of moderate and severe VI, and cataract was the leading cause of blindness.UREs were the leading cause of VI in the younger age group (16-59 years), and cataract was the leading cause of VI in the older age group (60 years and older) (figure 1).

Temporal trends in VI
The data of individuals aged ≥40 years examined in the 2014 and 2021-2022 studies were analysed to capture the Open access trends in the prevalence of VI over time. 14

DISCUSSION
We have reported on the prevalence and causes of VI among the adult population in the Nirmal district of Telangana using the extended RAVI methodology.The conventional RAAB and RAVI methods include individuals aged ≥50 years and ≥40 years, respectively.In contrast, the extended RAVI methodology used in this study included anyone aged ≥16 years.While it is advantageous to only include the older population to minimise the sample size and use of resources, the data on VI are not readily available in the younger age groups.Data on all ages are essential to plan universal eye health initiatives in the region.The extended RAVI is an attempt to provide comprehensive information on the prevalence of VI in the complete adult population in this region.The data from this study can supplement the data from school eye health programmes, providing a complete picture of VI in the entire population, other than children under 5 years.In addition, we used the revised WHO definitions in this study for cross-comparison with other studies done in India and other regions of the world.
The Andhra Pradesh Eye Disease Study (APEDS) conducted between 1996 and 2000 was the only population-based cross-sectional study that included the population of all ages.The prevalence of moderate VI, severe VI and blindness was 10.1%, 2.3% and 2.3%, respectively. 19 20Using similar definitions, the prevalence of moderate VI, severe VI and blindness in this study was 4.6%, 0.60% and 0.69%, respectively. 19 21The prevalence of Mild VI is not reported in APEDS.Despite a difference in the age groups between the studies, a lower prevalence in this study indicates a decline in the prevalence of VI in this region over the last three decades.Such a secular trend of decline in VI has been reported from various locations, suggesting an improvement in the availability and uptake of eye care services in this region.
Both APEDS and the current study had a higher prevalence of VI among the older participants, which is consistent across all the studies conducted in this region. 19 21n this study, though the prevalence did not vary with gender, women had lower odds for VI, which is contrary to the APEDS study, where women had a higher prevalence of VI.This difference could be attributed to the availability, acceptability and a higher uptake of eye care services among women.A higher prevalence of VI was also noted among those with lower levels of education, which is similar to other studies in this region. 11 14 19 21The higher visual needs and availability of resources for eye examinations and treatment might have contributed to a lower prevalence of VI among those with higher levels of education.The participants who self-reported diabetes had a higher prevalence of VI in this study, which might be caused due to an earlier onset of cataract secondary to diabetes and other refractive changes in the eye.
Several studies have reported the prevalence of VI using the RAVI methodology among participants aged

Table 1
Visual impairment (VI) and demographic characteristics of the participants

Table 3
Effects of sociodemographic variables on visual impairment (multiple logistic regression analysis) Figure1Causes of visual impairment across the age groups.

Table 4
Prevalence of visual impairment in Nirmal district in Telanagana, India as reported in various studies APEDS, Andhra Pradesh Eye Disease Study; RACSS, Rapid Assessment of Cataract Surgical Services; RAVI, Rapid Assessment of Visual Impairment.