Article Text

Download PDFPDF

Original article
Efficacy of a remote based computerised visual acuity measurement
  1. Krithica Srinivasan,
  2. S Ve Ramesh,
  3. Noushad Babu,
  4. Nijil Sanker,
  5. Avik Ray,
  6. S M Karuna
  1. Department of Optometry, Manipal College of Allied Health Science, Manipal University, Karnataka, India
  1. Correspondence to S Ve Ramesh, Department of Optometry, Manipal College of Allied Health Science, Manipal University, Manipal, Karnataka 576104, India; ramesh.sve{at}


Aim To determine the efficacy of a remotely operated computer-based logarithmic (logMAR) visual acuity chart.

Methods Visual acuity was tested using a laptop or computer-based logMAR chart (COMPlog) for all subjects by two different methods. The methods differed by the physical presence and absence (remote) of an optometrist and in the mode of instructions provided. Remote access was obtained through the internet, using Teamviewer software to control the system linked to COMPlog and instructions were provided by telephone. The order of measurements and the eye to be tested was randomised. logMAR visual acuity and time taken were recorded. A questionnaire was used to assess the participant's feedback.

Results Intraclass correlation for visual acuity between the two methods (α=0.964, 95% CI 0.937 to 0.979). There was no statistically significant difference (p=0.648) in the median visual acuity measurement between the two methods (median difference 0.00, IQR 0.20 logMAR). The time taken between the two methods was not statistically significant (p=0.457). There was no significant difference in the responses to the questionnaire between the study methods (p=0.119).

Conclusions Tele (remotely controlled) visual acuity measurement is as reliable as that measured with the physical presence of an optometrist.

  • COMPlog
  • epidemiology
  • field of vision
  • glaucoma
  • optic nerve
  • remote
  • tele screening
  • vision
  • visual acuity

Statistics from

Over 161 million people were visually impaired, of whom 37 million were blind across the world as at 2002.1 The recent estimation from the WHO shows a significant increase of approximately 285 million people being visually impaired across the world, of whom 39 million are blind.2 The prevalence of blindness is not distributed uniformly throughout the world—lesser developed countries have more people with blindness than developed countries.1 The prevalence, awareness, knowledge and uptake of facilities vary significantly between the urban and rural populations, impairing the implementation of healthcare facilities in India.3 ,4 Using effective screening methods to detect the at-risk population followed by a comprehensive eye examination would be an appropriate way to reduce preventable blindness. However, performing a standard vision examination on every individual is a challenging task, and factors such as the lack of infrastructure and a dearth of qualified primary eye care practitioners are the major issues.

Visual acuity is the basic and pertinent parameter needed for both the detection and management of any ocular malady. There are only 12 eye care practitioners per million population in Asia.5 As a result of this lack of qualified healthcare professionals, non-health professionals such as social workers, teachers and student volunteers are trained for visual acuity screening, but the validity of such screening is limited and variable.3 One of the solutions for cost-effective and quality eye care delivery is through tele-based eye screening in which qualified professionals perform the standard visual assessment either in real time or performing in person.6

The conventional Snellen acuity chart provides unreliable visual acuity measurements and is considered to be outdated.7 Logarithmic (logMAR) acuity charts provide more accurate and repeatable estimates of patients' visual acuity and are the recommended modality worldwide. This could be used as an effective tool in identifying at-risk populations with refractive error and sight-threatening eye diseases such as diabetic retinopathy, macular degeneration, etc.8 The recent advent of computerised logMAR acuity charts are a substitute for the conventional printed chart. Therefore, we intend to determine the efficacy of a remotely operated computer-based logMAR visual acuity chart.


The current study was conducted on willing participants among the university students and staff of Manipal College of Allied Health Science, Manipal University, Karnataka, India. All subjects signed a written informed consent and the study was accepted by the institutional review board.

Visual acuity was tested using a computer-based logMAR chart: COMplog (Ver 1.3.13; Medisoft Inc, UK). Laidlaw et al9 reported the clinical validity of COMPlog on 59 children and 70 adults and they report good agreement with conventional ETDRS and electronic ETDRS charts. The inclusion criterion was uncorrected visual acuity better than or equal to 6/60 vision. The order of testing (remote or optometrist controlled) and the eye to be tested were also randomly assigned, random number generated in blocks of 10. Only one randomly selected eye of each subject is tested for visual acuity. The visual acuity and time taken to perform the procedure for both optometrist and remote controlled protocol were recorded. Subjects with any history of ocular trauma, surgery and/or not willing to participate were excluded from the study.

COMPlog visual acuity screener

COMPlog is a computerised logMAR chart, is user friendly and a validated visual acuity measurement tool.9 It is a visual acuity measurement software, operated through a laptop PC (Windows system) and the patient views the letter on a secondary monitor (24 in, 1600×1200 resolution LED flat panel). The secondary monitor was calibrated for 3 m distance for performing acuity measurements. The optometrist controlled the test and graded whether the patient's responses were correct or incorrect on the laptop (figure 1). The software runs an acuity screener to identify quickly the rough visual acuity of the patient and further refines using a thresholding technique.

Figure 1

COMPlog visual acuity measurement. Top-acuity screener, bottom-thresholding method, these control displays appear in both remotely and optometrist-controlled visual acuity measurement methods.

  • Step A: In the acuity screening, the test starts with a single letter of size 0.8 logMAR with crowding bars on all four sides.

  • Step B: With every correct response, the software presents a new letter two logMAR lines smaller than the previous line until the letter is incorrectly identified.

  • Step C: With every wrong response the software presents a single line of five letters and the response to individual letters is scored to calculate the accurate logMAR acuity.

  • Step D: The lines of random selected letters are presented one logMAR line smaller than the previous line until a complete line is incorrectly identified. This is considered the endpoint and the visual acuity of the patient is recorded and stored on the computer.

Remote control of COMPlog and patient instruction

Internet connectivity was established on two laptops, using commercially available broadband plug and play mobile internet devices. One of the laptop was linked to the COMPlog unit and the other was used to access this from a different location in the premises through the internet. Both the units were physically apart so as to ensure there was no direct bias in providing instruction and in test performance. Team Viewer (Team Viewer version 7, Teamviewer GmbH, Goppingen, Germany) is a free software that assists in remote access and control of any computer or server through the internet. In this study we assessed the efficacy of performing visual acuity using COMPlog and performing the test using Team Viewer, thereby controlling the test in a remote mode. Team Viewer software was installed on both laptops and the remote connection was established from the second laptop as and when the participants were ready for remote examination. Patient instructions were provided through telephone conversation and a trained optometrist performed visual acuity examination, both in person and through remotely controlled modes. Patient details were entered separately; the procedure was performed with the physical absence of the optometrist in the examination room. They were also masked from the previous visual acuity measurements.

A custom-developed questionnaire was used to assess the participants' comfort and ease of administering visual acuity through telephone and remote-based medium (see supplementary appendix 1, available online only). The questionnaire was used to grade (scale of 0 worst to 5 best) the comfort level, clarity of instruction and happiness of being examined in person and through remotely controlled methods. Final visual acuity logMAR values obtained and the statistical comparison was performed using the Wilcoxon sign rank test and statistical significance was considered for p<0.05. Bland–Altman plots were obtained and the limits of agreement between the test methods were obtained and clinical agreement was determined.


Of the 61 screened, a total of 52 (85.3%, 95% CI 74.3 to 92.0) subjects were eligible for the study. The mean age of the study population was 23 years (SD 6.1, range 18–51) and 67.3% (95% CI 53.8 to 78.5) were women participants. In the random order, 53.8% (95% CI 40.5 to 66.7) underwent remote examination first and 51.9 (95% CI 38.7 to 64.9) had the right eye examined. The median difference in visual acuity between the two methods was 0.00 logMAR. There was no statistically significant difference (p=0.648) in the median visual acuity measurement between the two methods (table 1). Similarly, the median difference in time taken to measure visual acuity between the two methods was 0 s (p=0.457) (table 1). Figure 2 shows the Bland–Altman plot, the mean difference between remote and optometrist controlled methods. The upper and lower 95% limits of agreement were 0.26 and −0.26 logMAR units, respectively. There was very good intraclass correlation for visual acuity between the two methods (α=0.964, 95% CI 0.937 to 0.979). For all questions, over 84.62% (95% CI 72.48 to 91.99) of the study population provided scores above four for remote examination, and 13.46% (95% CI 6.68 to 25.27) complained of poor clarity in instruction and telephone conversation. The responses for the question on the clarity of instruction given in both the methods were not statistically significant (Wilcoxon sign rank test, p=0.808). The responses were further categorised into two groups as scores ≤3 (bad experience) and >3 (good experience). Table 2 shows the percentage of responses among these categories. There was no significant difference in the categorised responses for all the three domains (comfort, clarity, happiness) between the remote and optometrist controlled study methods (χ2 test, p=0.119).

Table 1

Comparison of mean visual acuity measurements and time taken to perform COMplog vision between remotely and optometrist-controlled methods

Table 2

Distribution of questionnaire responses across domains

Figure 2

The difference versus average (Bland–Altman) plot between remote and optometrist-controlled COMPlog visual acuity (VA) measurements.


The current study showed that visual acuity measurements performed through a remote telephone mode were as comparable with the measurements made by an optometrist in person in a university population. There was very good correlation between the two modalities (intraclass correlation 0.964). There was no statistically significant difference between the two measurements (p=0.648) and the 95% limits of agreement ranged from +0.26 to −0.26 logMAR.

Tele-based eye screening methods currently show an emphasis on improving strategies to detect retinal pathologies.10 The current study throws light on assessing in real time the functional visual acuity measurement in patients using a computerised logMAR acuity chart. Effective telemedicine practice could be established by incorporating vital information through real-time access and this is being advocated as a sustainable model.6 ,10 We report that real-time assessment of visual acuity through a remotely operated mode is a new feasible modality of vision screening. This mode of remote control real-time eye screening presents further scope for including objective and subjective refraction techniques using computer-controlled instrumentation.

Vision screening is performed using a wide variety of rapid screening tools such as finger counting, Snellen acuity drum, 3 m Snellen acuity chart and logMAR acuity charts.3 ,7 The lack of trained professionals and the usage of non-standard charts for visual acuity measurement impairs the efficacy of regular vision screening.3 LogMAR-based pocket vision screeners are useful in mass screening,11 but such tools do not provide true visual acuity measurements. COMPlog provides accurate and reliable measurements of vision and could be very useful in monitoring vision during follow-up visits. Laidlaw et al9 compared COMPlog with conventional ETDRS charts and showed a test–retest variability of ±0.12 and ±0.10 logMAR units among amblyopia and adult study group, respectively. The authors also reported a variability of ±0.16 logMAR for electronic ETDRS charts. In the current study COMPlog measurements performed in a remotely controlled mode showed relatively lower and clinically acceptable variability (±0.14 logMAR). Clinically, an individual's logMAR visual acuity needs to change by more than two lines (0.2 logMAR) to be considered as a significant change.12 The difference observed in the remote visual acuity assessment could also be attributed to the deficit of using only telephone conversations for providing instruction. It is reported that an audio and visual conversation between the doctor and patient enhances the patient's satisfaction in tele-based eye screening.13 In the current study, although over 84% reported a good comfort level and were happy being examined through a remote mode, approximately 13% complained of poorer clarity in telephone conversations. Lower variability and better reproducibility would be expected if live one-to-one video interaction and patient training videos are included in remote vision screening.

We report a novel method of using COMPlog and Team Viewer software to monitor and record reliable logMAR acuity measurements remotely compared with measurements made by an optometrist in person.



  • Competing interests None.

  • Patient consent Obtained.

  • Ethics approval Ethics approval was obtained from the Institutional Review Board, MCOAHS, Manipal University, Karnataka, India.

  • Provenance and peer review Not commissioned; externally peer reviewed.

Request Permissions

If you wish to reuse any or all of this article please use the link below which will take you to the Copyright Clearance Center’s RightsLink service. You will be able to get a quick price and instant permission to reuse the content in many different ways.

Linked Articles

  • At a glance
    Harminder Singh Dua Arun D Singh