Conversion of Snellen visual acuity fractions to approxETDRS letter scores for the purpose of performing statistical manipulations provides more readily interpretable outcomes compared with the current strategy of converting Snellen visual acuity fractions to logMAR units. In the clinical setting, there is still a mixed use of Snellen acuity charts and ETDRS acuity charts. This chapter explains how you can improve names and codes so that eye will work like a charm. The term LogMAR is an acronym for the Logarithm of the Minimum Angle of Resolution. proposed the line scoring method [3]. Will find the eye column, unify the codes for the eyes (all to r and l) and pivot the columns wide, that have been specified in cols. Schulze-Bonsel et al. 2009 Dec;107:311-24. A more intuitive approach is presented here which uses the conversion of Snellen visual acuity fractions to Early Treatment Diabetic Retinopathy Study (ETDRS) letter scores for statistical manipulations. endobj endobj Although kind of nice, blink is more a nerdy extra and is not likely to be used much. ## But which dimension of "r"/"l" are we exactly looking at? 3,575,655. P30 EY014801/EY/NEI NIH HHS/United States. Decimal Snellen fractions MAR LogMAR 6m 5m 4m 3m 20ft 10ft 0.010 6/600 5/500 4/400 3/300 20/2000 10/1000 100 2.0 0.012 6/480 5/400 4/320 3/240 20/1600 10/800 80 1.92 For example, in Peden et al., Snellen VAs were retrospectively collected from records and converted to letter values 'in a standard fashion for statistical analy-sis'.12 Graphs misleadingly include Y-axes of 'ETDRS let-ters' with gure 5 scores averaging around 60 letters (0.50 logMAR, Snellen 6/18, 20/60), whereas the patient has [in press]. https://doi.org/10.1016/s0002-9394(02)01825-1. Conversion of Snellen visual acuity fractions to approxETDRS letter scores for the purpose of performing statistical manipulations provides more readily interpretable outcomes compared with the current strategy of converting Snellen visual acuity fractions to logMAR units. will force to evaluate from which notation to convert - Must be Provided by the Springer Nature SharedIt content-sharing initiative, International Journal of Retina and Vitreous (2022), Eye (Eye) You can capitalise the first number with the caps argument. Ophthalmic Physiol Opt. Bailey and Lovie created their own modified version of the Snellen chart to reduce some of its inaccuracies. From Snellen to ETDRS | M&S Technologies <> Elsevier BV: 194205. or "", "n/a" or " ". (Also see related commentary by Andrew P. Schachat, MD, and Marco A. Zarbin, MD, in the same issue. Suprachoroidal injection of triamcinolone acetonide plus intravitreal bevacizumab in diabetic macular edema: a randomized pilot trial. eyes recognizes integer coding 0:1 and 1:2, with right being the lower number. will force to evaluate from which notation to convert - Must be VA cleaning Arguments Column C: letters gained (+) or missed (), ENTER INTO FORMULA BAR FOR CELL:=ROUND(LOG(B2/A2),2)(C2*0.02). if one of CF, HM, LP, PL, NLP, or NPL: Snellen fractions (meter/ feet) need to be entered as fraction with /. It can be rear or front illuminated. A linear relationship exists . We examined two different methods of scoring individual letters on a Snellen chart. This may then result in a vector of "mixed" VA notations. "etdrs", "logmar", "snellen" or "snellendec". All told, 413 patients (773 eyes) met the inclusion criteria for this study. The site is secure. The cols argument takes a tidyselection. See also "VA classes", logMAR to ETDRS: logMAR rounded to the first digit and converted with Description PubMedGoogle Scholar. Anyone you share the following link with will be able to read this content: Sorry, a shareable link is not currently available for this article. Correspondence to Even more so, as the given conditions should work for charts with 4 or 5 optotypes in a line, and visual acuity is not always tested on such charts. New visual acuity charts for clinical research. To which Snellen notation to convert: "m", "dec" or "ft", how +/- entries are evaluated. Both accept tidyselection. 5 0 obj Effect of letter separation on computerised visual acuity measurements: comparison with the gold standard Early Treatment Diabetic Retinopathy Study (ETDRS) chart. As each row grew smaller, the amount of space between each row decreased. For access, try logging in If you are subscribed to this group and have noticed abuse, report abusive group. This argument can be overriden with noplus = TRUE, ignoring the plus minus entries entirely and simply returning the nearest Snellen values. endobj If there still are variables spread over two columns for right and left eyes, then this is an example of messy data. Most retrospective reviews convert Snellen visual acuity measurements obtained during routine clinic visits to logarithm of the minimum angle of resolution (logMAR) units so that statistical manipulations can be performed. Standardized ETDRS Testing - VectorVision "/". Conversion directly from one cell of Snellen fraction into another cell without manipulation or re-formatting of the original Snellen fraction (Fig. This is intended for integration into rmarkdown reports, or for easy copy / pasting. endstream Distances between lines were not consistent. hand movement and (no) perception of light, use logMAR ! #> Unclear which is the eye column. See Fig. Read reviews, compare customer ratings, see screenshots and learn more about Visual Acuity. similar and uniform legibility of each line and offer an ease of conversion of VA to a logarithmic scale. Holladay J. For more information, please refer to our Privacy Policy. Entries with mixed VA notations doi: 10.1016/s0002-9394 (02)01825-1 Hand movements and counting fingers are converted following Schulze-Bonsel et al. Gregori et al.doi: 10.1097/iae.0b013e3181d87e04. numeric (for logMAR), or integer (for ETDRS). [4], The chart was designed by Ian Bailey[5] and Jan E. Lovie-Kitchin at the National Vision Research Institute of Australia. endobj The etdrs values for NLP and PL are deliberately set at those values because vector of va class. and JavaScript. The Apple iPod Touch (Figure 2), communicating with the EVA PC via Wi-Fi, provides . 2023 M&S Technologies Please enable it to take advantage of the complete set of features! The formula is subsequently validated with manual conversion by two independent clinicians (CL and TS). For example, eight columns that store data of four variables for right and left eyes will be pivoted to 5 columns (one eye column and four further variable columns)). By default, plus/minus entries are evaluated as intended by the Using ANOVA, this difference between testing times was. Ferris FL, Kassoff A, Bresnick GH, Bailey I. Other VA converter: The mean difference was 1 letter (0.0195 LogMAR) better on ETDRS chart when compared to Snellen chart. - https://doi.org/10.1167/iovs.05-0981, (No) light perception are converted following the suggestions by It is more user friendly, since it avoids decimal values and is more intuitive, since higher values indicate better vision. 8 0 obj Stephenie Tiew. The Bailey-Lovie chart was also designed to be scored in logMAR units, making it easier to convert results based upon various viewing distances. Charles RC, Frost NA. To Snellen: 13 0 obj CAS However, additional letters read or missed letters are not accounted for. The formula to convert Snellen visual acuity measurements to approxETDRS letter scores is 85 + 50 x log (Snellen fraction), which may be rounded to the nearest letter. & Tiew, S. Using an excel spreadsheet to convert Snellen visual acuity to LogMAR visual acuityfurther explanation. Kucukevcilioglu M, Yeilta YS, Durukan AH, Unlu N, Onen M, Alp MN, Kalayci D, Acar MA, Sekeroglu MA, Citirik M, Altintas AGK, Hazirolan D, Ozdal PC, Toklu Y, Bicer T, Ugurlu N, Budakoglu O, Yazar Z, Zeki NIU, Serdar K, Doguizi S, Erol YO, Atilgan CU, Yorgun MA, Soba DO, Berker N, Baskan C. Medicina (Kaunas). You may search for similar articles that contain these same keywords or you may Plausibility checks are performed for the automatically or manually defined ETDRS charts (within about 2% of the letter size at each logMAR level). Snellen Notation (logMAR to Snellen conversion for 65 letters): 20/50. Qualitative visual acuity lower than counting fingers is assigned 0 #> blink , #> Data , #> , #> 1 a right TE 21 11 0.88 0.80, #> 2 a left TE 31 11 0.88 0.80, #> 3 b right TE 22 12 0.86 0.78, #> 4 b left TE 32 12 0.86 0.78, #> 5 c right SLT 23 13 0.84 0.76, #> 6 c left TE 33 13 0.84 0.76, #> 7 d right SLT 24 14 0.82 0.74, #> 8 d left SLT 34 14 0.82 0.74, #> Count of patient and eyes , #> Counts , #> Visual acuity , #> Intraocular pressure , #> $IOP_eyes (right and left eyes), #> Warning: Data seems already myopic - no changes made. eye works smoother with tidy data, and with good names (any package does, really!). integer coding 0:1 and 1:2, right eye being the lower number. From the *Department of Ophthalmology, Bascom Palmer Eye Institute, University of Miami Miller School of Medicine, Miami, Florida; and the Ophthalmology Service, Miami Veterans Affairs Medical Center, Miami, Florida. PDF Snellen ETDRS Snellen Letters 2.00 100 20/10 6/3 -0.3 1.60 - Ophtha.ch Before Visual Acuity - SPIE Correspondence to Pesky visual acuity notations are now a matter of the past. The letter size is described in LogMAR units where LogMAR 0.00 is equivalent to 6/6 (20/20) in snellen scale or 85 ETDRS letter Score. The VAS scale (VAS = Visual Acuity Score) serves the same purpose. Results: The chart was developed at the National Vision Research Institute of Australia in 1976, and is designed to enable a more accurate estimate of acuity than do other charts (e.g., the Snellen chart). Each class can be converted from one to another. All Snellen and ETDRS VA measurements were converted to logMAR units for direct comparison, and the variability between measurements was calculated. Data is temporarily unavailable. Better just "VA", #> [1] "Id" "Eye" "FollowupDays" "BaselineAge", #> [5] "Gender" "VA_ETDRS_Letters" "InjectionNumber". Google Scholar. The Snellen visual acuity (VA) chart is routinely used in clinical practice, while that developed in the Early Treatment Diabetes Retinopathy Study (ETDRS) is the gold standard for ophthalmic clinical trials. Michael Bach. 2 0 obj I do not assume responsability for your data or analysis. ), logMAR and ETDRS. You are using a browser version with limited support for CSS. TRUE: plus/minus Since there are 5 letters per line, the total score for a line on the LogMAR chart represents a change of 0.1 log units. Indeed, in my experience R often needs eyes to be in a single column, with each other variable having their own dedicated column. For entries with mixed notation, use va_mixed instead. Clipboard, Search History, and several other advanced features are temporarily unavailable. By default, numbers smaller than or equal to 12 will be real English, all other numbers will be numbers. LogMAR chart - Wikipedia <> 2023 Jan 19;9:1100241. doi: 10.3389/fmed.2022.1100241. However, visual acuity measurements expressed as logMAR units are not intuitively interpretable by clinicians. 10.1016/s0002-9394 (02)01825-1 Beck, Roy W, Pamela S Moke, Andrew H Turpin, Frederick L Ferris, John Paul SanGiovanni, Chris A Johnson, Eileen E Birch, et al.2003. A Computerized Method of Visual Acuity Testing. American Journal of Ophthalmology 135 (2). endobj volume34,pages 21482149 (2020)Cite this article. Excel spreadsheet picture depicting an example of Snellen VA 6/122 and 6/12+2 with their respective logMAR equivalents. eCollection 2022. Basically the opposite of myop() - a slightly intelligent wrapper around tidyr::pivot_longer() and tidyr::pivot_wider(). Beck et al. 15 0 obj stream 8,425,040; 8,550,631; 10,244,938; and 10,182,713. Real Life Multicenter Comparison of 24-Month Outcomes of Anti-VEGF Therapy in Diabetic Macular Edema in Turkey: Ranibizumab vs. Aflibercept vs. Ranibizumab-Aflibercept Switch. Snellen acuity is given in terms of a Snellen fraction S, which is defined as Typical testing distances for the Snellen chart are 20 feet and 6 meters. In the meantime, to ensure continued support, we are displaying the site without styles The https:// ensures that you are connecting to the Convert Snellen to logMAR Snellen numerator: Snellen denominator: Convert logMAR to Snellen logMAR: Usage: In addition to interactive use of the calculator, links to the calculator may contain either logMAR or Snellen values that will be automatically evaluated. ## automatic detection of VA notation and converting to logMAR by default, #> [1] "20/320" "20/80" "20/32" "20/70", ## And the decimal snellen notation, so much loved in Germany, ## Remove weird entries and implausible entries depending on the VA choice, #> From snellen. 2017 Jun 1;135(6):651-653. doi: 10.1001/jamaophthalmol.2017.0932. <> set out to compare the variability between the two measurements of best-corrected visual acuity (BCVA). <> Our data set consists of 100 patients who underwent corneal collagen cross linking. The ESV-3000 allows testing up to 20/200 ETDRS Acuity at a test distance of 4 meters The device is operated by infrared remote control. % Am J Ophthalmol. PDF Visual Acuity Score Conversion - Jaeb Must be atomic. Front Med (Lausanne). [ 14 0 R] The formula can be copied and paste into the subsequent cells in the logMAR column (column D) to facilitate bulk analysis of data. Visual Acuity Testing (Snellen Chart) - MDCalc and transmitted securely. back to Snellen, it is a very natural thing to eye specialists to think https://doi.org/10.1097/iae.0b013e3181d87e04. ## If the dimension is already part of the column names, this is not necessary. 1 for an example of our spreadsheet. Using an excel spreadsheet to convert Snellen visual acuity to - Nature acuity for the patients are. Google Scholar. Vision Research 90: 2-9. Holladay, Jack T. 2004. Visual Acuity Measurements. Journal of Cataract and Refractive Surgery 30 (2): 28790. Comparison of the ETDRS logMAR, 'compact reduced logMar' and Snellen Using an excel spreadsheet to convert Snellen visual acuity to - Nature the VA chart are used. doi: 10.1097/iae.0b013e3181d87e04, ETDRS to logMAR: logMAR = -0.02 * etdrs + 1.7 It will return a list object which gives you easy access to the data. see "Examples", ETDRS must be integer-equivalent between 0 and 100 (integer equivalent 2023 Jan 27;23(1):40. doi: 10.1186/s12886-023-02790-y. endobj National Vision Research Institute of Australia, Early Treatment Diabetic Retinopathy Study, "Reading aids for adults with low vision", https://en.wikipedia.org/w/index.php?title=LogMAR_chart&oldid=1135496931, LogMAR VA = 0.1 + LogMAR value of the best line read 0.02 X (number of optotypes read), LogMAR VA = LogMAR value of the best line read + 0.02 X (number of optotypes missed), This page was last edited on 25 January 2023, at 00:42. The PubMed wordmark and PubMed logo are registered trademarks of the U.S. Department of Health and Human Services (HHS). Conversion of Snellen visual acuity to LogMAR visual acuity. 1) hence reducing risk of transcription errors. It is very - https://doi.org/10.1167/iovs.05-0981 Snellen to logMAR: logMAR = -1 * log10(snellen_frac) Snellen to ETDRS: ETDRS = 85 + 50 * log10(snellen_frac) Gregori et al.. ETDRS to logMAR: logMAR = -0.02 * etdrs + 1.7 Beck et al. <> Kaiser PK. 10 0 obj Its formula is: 100 - 50 x logMAR or 100 + 50 x log (V). PubMedGoogle Scholar. Conversions Between Letter, LogMAR, and Snellen Visual Acuity Scores Internet Explorer). 4 0 obj Chen FK, Agelis LE, Peh KK, Teong J, Wong EN. va: Visual acuity notation conversion in eye: Analysis of Eye Data Coney JM, Zubricky R, Sinha SB, Sonbolian N, Zhou L, Hull TP, Lewis SA, Miller DG, Novak MA, Pendergast SD, Pham H, Platt SM, Rao LJ, Schartman JP, Singerman LJ, Donkor R, Fink M, McCoy J, Karcher H. Int J Retina Vitreous. Or, arguably more appropriate in R, character coding for a categorical variable: you can change those codes with set_eye_strings(). endobj Vector with visual acuity entries. plausibility_methods, To which class to convert. endobj Visual acuity testing. <> . The interconversion between Snellen visual acuity measurements, logMAR units, and approxETDRS letter scores was prepared in a tabular form for easy reference. For more information on customizing the embed code, read Embedding Snippets. the best experience, we recommend you use a more up to date browser (or turn off compatibility mode in [Landolt C and snellen e acuity: differences in strabismus - PubMed "etdrs", "logmar" or "snellen" - Snellen-Logmar Calculator - Visual Impairment Network for Children Visual acuity is a vital outcome measure in determining efficacy of treatments and interventions in ophthalmology. For this study, the authors assessed data from 12 prospective clinical trials conducted at a large urban retina practice in the United States. [Repeatability and reliability of the visual acuity examination on logMAR ETDRS and Snellen chart]. eyes offers a very simple tool for counting patients and eyes. %PDF-1.5 endobj FOIA This is a simple function and should not require much explanation. Trabelsi O, Bouladi M, Ouertani A, Trabelsi A. Clin Ophthalmol. Prospective evaluation of visual acuity assessment: a comparison of snellen versus ETDRS charts in clinical practice (An AOS Thesis). <> In order to calculate with qualitative entries counting fingers, considered an exact science and any attempt to use formulas will result You can also more globally change recognized codes with set_eye_strings(). ETDRS letter, in order to keep it as a measurement (not: NA). M&S holds US Patent Numbers 7,354,155; 7,926,948; 8,167,429; 8,419,184; https://doi.org/10.1167/iovs.05-0981. VAwrapper, 2010 Mar;30(2):200-3. doi: 10.1111/j.1475-1313.2009.00700.x. Usage 16 0 obj VA Variability: Snellen Versus ETDRS Outcomes in Snellen. Reprint requests: Philip J. Rosenfeld, MD, PhD, Bascom Palmer Eye Institute, 900 NW 17th St., Miami, FL 33136; e-mail: [emailprotected]. doi: 10.1016/s0002-9394(02)01825-1Beck et al., and VA classes va_mixed(), Please try after some time. va_methods, This chart and VA conversion formulas are based on charts in va: Visual acuity notation conversion in tjebo/eye: Analysis of Eye Data You can find with eye:::va_chart. between Snellen (decimal, meter and feet), ETDRS, and logMAR. In the meantime, to ensure continued support, we are displaying the site without styles ISSN 0950-222X (print), Using an excel spreadsheet to convert Snellen visual acuity to LogMAR visual acuity, https://doi.org/10.1038/s41433-020-0783-6, Three-dimensional heads-up system assisted pars plana vitrectomy and subretinal recombinant tissue plasminogen activator injection for submacular hemorrhage, Anatomical and functional outcomes of retinal detachment associated with nontraumatic giant retinal tears compared to simple rhegmatogenous retinal detachment, Stabilization of refractive error and associated factors following small incision phacoemulsification cataract surgery, Effect of time to operative repair within twenty-four hours on visual acuity outcomes for open globe injuries, Comment on: Conversion of Snellen visual acuity to LogMAR visual acuity. When VA was assessed by subgroups, eyes with worse vision had a greater difference between Snellen and ETDRS scores: Eyes 20/25 or better were a mean +1.9 letters better on ETDRS testing, and eyes 20/160 or worse were a mean +12.6 letters better on ETDRS testing (p < .05 for both). If NULL (default), will simply "clean up" VA entries. Could be etdrs, logmar, snellendec. ## will automatically detect VA class and convert to logMAR by default, ## snellen, mixed with categories. See also Examples. For some more details see VA conversion. ?myop for help, #> From etdrs. [1] For this reason, the LogMAR chart is recommended, particularly in a research setting.[2]. 2006. Visual Acuities Hand Motion and Counting Fingers Can Be Quantified with the Freiburg Visual Acuity Test. Investigative Ophthalmology & Visual Science 47 (3): 123640. M]D_*zcP?VpON`7?44N]p+8arMa*\ Donders diagnosed vision problems by asking people to look at a chart on a wall and tell him what they could see. Thus, the authors said, the specific retinal disease state and extent of edema may play a role in the variability between the measurements. All Snellen and ETDRS VA measurements were converted to logMAR units for direct comparison, and the variability between measurements was calculated. Contact Us and let us know. ISSN 1476-5454 (online) The same outcomes (in Snellen fractions) were obtained with statistical manipulation of either approxETDRS letter scores or logMAR conversions. any case allowed. Smart System Reg U.S. Pat. Article logMAR - Snellen Conversion Calculator ::: MyVisionTest.com To Snellen: Gregori, Ninel Z, William Feuer, and Philip J Rosenfeld. Tiew S, Lim C, Sivagnanasithiyar T. Using an excel spreadsheet to convert Snellen visual acuity to LogMAR visual acuity. It will look for VA and for IOP columns and provide the summary stats for the entire cohort and for right and left eyes for each VA and IOP variable. <> This, again, requires a certain format of names and codes - See Names and Codes. These conversions were done via our excel spreadsheet formula taking into account methods from our literature searches. As for myop and of course blink, a specific column naming is required for a reliable automatic detection of patient and eye column(s) ( see Names and codes). You can read the full text of this article if you: Keywords If you are not happy with the automatic column selection, you can manually select the VA and IOP columns with the arguments va_cols or iop_cols. Holladay et al.doi: 10.1016/j.jcrs.2004.01.014, Beck et al. Visual Acuity Variability: Comparing Discrepancies between Snellen and Eye 34, 21482149 (2020). It takes an (atomic) vector with visual acuity entries as the only required argument. EDITORIAL The good (logMAR), the bad (Snellen) and the ugly (BCVA Please try again soon. endobj However, back-conversion should not be See names and codes If there is already a column called eye or eyes, myop will not make any changes - because the data is then already assumed to be in long format. reveal() takes the grouping argument by and it returns vector for atomic vectors or a data frame for lists. R: Visual acuity notation conversion Could be snellen, logmar, snellendec, etdrs, #> 6x NA introduced for: 0.8, 34, , ., -, NULL, #> [1] "20/20000" NA NA "20/400" "20/2000" "20/50", #> [7] NA NA NA NA, #> 8x NA introduced for: 34, 3/60, 2/200, 20/50, , ., -, NULL, #> [1] "20/20000" "20/25" NA NA NA NA, #> 8x NA introduced for: 0.8, 3/60, 2/200, 20/50, , ., -, NULL, #> [1] "20/20000" NA "20/200" NA NA NA, #> [1] "20/20000" "20/125" NA NA NA NA, ## "plus/minus" entries are converted to the most probable threshold (any spaces allowed), ## or evaluating them as logmar values (each optotype equals 0.02 logmar), ## or you can also decide to completely ignore them (converting them to the nearest snellen value in the VA chart), #> [1] "20/200" "20/20" "20/50" "20/20" "20/32", #> [1] "r" "r" "r" "r" "l" "l" "l" "l" "b" "b", #> [1] "od" "od" "od" "od" "os" "os" "os" "os" "ou" "ou", #> Missing values and/or meaningless strings contained, ## If you are using different strings to code for eyes, e.g., you are using a different language, you can change this either with the "eyestrings" argument, ## or change it more globally with `set_eye_strings`, # to restore the default, call set_eye_strings empty. 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Therefore, Snellen matching the nearest ETDRS and logMAR value in Google Scholar, Department of Ophthalmology, University Hospitals of Leicester NHS Trust, Infirmary Square, Leicester, LE1 5WW, UK, Stephenie Tiew,Christina Lim&Tharsica Sivagnanasithiyar, You can also search for this author in Get new journal Tables of Contents sent right to your email inbox, NOVEL METHOD FOR ANALYZING SNELLEN VISUAL ACUITY MEASUREMENTS, Articles in PubMed by Ninel Z Gregori, MD, Articles in Google Scholar by Ninel Z Gregori, MD, Other articles in this journal by Ninel Z Gregori, MD, BACILLARY LAYER DETACHMENT: MULTIMODAL IMAGING AND HISTOLOGIC EVIDENCE OF A NOVEL OPTICAL COHERENCE TOMOGRAPHY TERMINOLOGY: Literature Review and Proposed Theory, GEOGRAPHIC ATROPHY INCIDENCE AND PROGRESSION AFTER INTRAVITREAL INJECTIONS OF ANTI-VASCULAR ENDOTHELIAL GROWTH FACTOR AGENTS FOR AGE-RELATED MACULAR DEGENERATION: A Meta-Analysis, CHOROIDAL INVOLVEMENT IN HEREDITARY TRANSTHYRETIN AMYLOIDOSIS PATIENTS, A NEW HEAVY SILICONE OIL (HWS 46-3000) USED AS A PROLONGED INTERNAL TAMPONADE AGENT IN COMPLICATED VITREORETINAL SURGERY: A Pilot Study, BIOCOMPATIBILITY OF BRILLIANT BLUE G IN A RAT MODEL OF SUBRETINAL INJECTION, Privacy Policy (Updated December 15, 2022). va_methods, Qualitative visual acuity lower than counting fingers is assigned 0 a specific range (0-100). see "Examples", ETDRS must be integer-equivalent between 0 and 100 (integer equivalent https://doi.org/10.1038/s41433-020-0783-6, DOI: https://doi.org/10.1038/s41433-020-0783-6. eyes also include a convenience function to turn the count into a text. A linear relationship exists between true ETDRS letter scores, approxETDRS letter scores, and logMAR units. unambiguous value to visual acuity, with non-arbitrary thresholds based on psychometric functions.