It is not really intended to replace other awesome data exploration packages / functions such as skimr::skim, and it will likely remain focussed on summarizing numerical data only. Vector with visual acuity entries. Bailey and Lovie created their own modified version of the Snellen chart to reduce some of its inaccuracies. The authors declare no competing interests. doi: 10.1016/s0002-9394(02)01825-1, Hand movements and counting fingers are converted following Read about tidyselection. This overrides the smallstep argument. Results: <> P30 EY014801/EY/NEI NIH HHS/United States. eye works smoother with tidy data, and with good names (any package does, really!). Or, arguably more appropriate in R, character coding for a categorical variable: you can change those codes with set_eye_strings(). Switching to brolucizumab: injection intervals and visual, anatomical and safety outcomes at 12 and 18months in real-world eyes with neovascular age-related macular degeneration. 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. Arguments to eyes_to_string are passed via : eyestr will create a string which you can paste into a report. endobj endobj Cleans and converts visual acuity notations (classes) 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. You can find with eye:::va_chart. 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)). hand movement and (no) perception of light, use logMAR ! This site needs JavaScript to work properly. & Tiew, S. Using an excel spreadsheet to convert Snellen visual acuity to LogMAR visual acuityfurther explanation. see "Examples", ETDRS must be integer-equivalent between 0 and 100 (integer equivalent If a subject can read a line at 20 feet and the "normal" observer can see the same line at 40 feet, then the subject has 20/40 Snellen acuity. Although there seems to be no good statistical reason to convert In the era of big data, there needs to be an efficient way of tidying up data to facilitate analysis. If there are only eye columns in your data (should actually not happen), myop will create identifiers by row position. Please try after some time. 19 0 obj RVACC Visual Acuity Testing Procedures Manual Revised 2013-02-15.docx Page 7 of 12 Show a 20/800 letter . equivalent to 0.02 logmar (assuming 5 letters in a row in a chart), NA is assigned to strings such as "." a specific range (0-100). Beck et al. endobj any case allowed. Roser DA, Laidlaw DAH, Murdoch IE. Beck et al. We measured their vision pre and post cross linking. ISSN 1476-5454 (online) Please enable it to take advantage of the complete set of features! The value of each letter was calculated by dividing. Google Scholar. Conversion of Snellen visual acuity to LogMAR visual acuity. You can also decide to simply clean your VA vector with cleanVA(x). [6] The formula used in calculating the score is: Given that each line has 5 optotypes, the equivalent formula is: The LogMAR chart is designed to enable more accurate estimates of acuity as compared to other acuity charts (e.g., the Snellen chart). No. ETDRS letter, in order to keep it as a measurement (not: NA). Correspondence to If smallstep = TRUE, each snellen optotype will be considered va_methods, But remember to put the strings for right eyes first, or pass a named list. Ovid Technologies (Wolters Kluwer Health): 104650. 2010 Mar;30(2):200-3. doi: 10.1111/j.1475-1313.2009.00700.x. Table: Different notations of visual acuity values as decimal values, Snellen fractions, MAR and LogMAR. <> 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. Snellen visual acuity measurements were converted to approximate ETDRS (approxETDRS) letter scores for statistical manipulations and then converted back to Snellen equivalent fractions. Using ANOVA, this difference between testing times was. ePd*D _@!(N|u!0!gL0F6?%='=N]baTcdCA?$wdEBjFOV{cP0 |1?28SjVH*5)y91M3z-wfr?X}wIt.,U3[,{x|.27w"FX`K K W;I D{c2drIDn?jokscrMjc-"Xv5Z3&p{-w/UnS200ue0 `8=e&"1w+8CE~2y'f%k>-$Ge;TGO^5EJ}bEBn>b%;-+k7, 6#:(ku(\EJcbCpsQu+1zhYmTGXLv"iQ=(6-Vc+)&RZ(Vd|FuiQM+EJ}bEj![XVU+1uY[(Vu+1+!E7\E=T@P[iTn'4]eQP'\]O[+#WFOIu >JI5)9Ejz1_h*:N7bg0ke rxn sharing sensitive information, make sure youre on a federal <> entries equivalent to 0.02 logmar. Examples. ISSN 1476-5454 (online) The .gov means its official. By default, plus/minus entries are evaluated as intended by the The name was chosen because its a contraction of eyes and strings and its a tiny bit easier to type than eyetxt. We present an excel spreadsheet formula to convert Snellen visual acuity to logMAR acuity. Specific types of logMAR chart include the original Bailey-Lovie chart,[3] as well as the ETDRS charts, developed for the Early Treatment Diabetic Retinopathy Study. 4 0 obj blink() is more than just a wrapper around myop(), eyes(), va() and reveal(). Prospective evaluation of visual acuity assessment: a comparison of snellen versus ETDRS charts in clinical practice (An AOS Thesis). ## If the dimension is already part of the column names, this is not necessary. Elsevier BV: 194205. to maintaining your privacy and will not share your personal information without eCollection 2023. <> <> However, just as all original technology does, there came a point when the Snellen chart needed reform. Counting id only. eyes recognizes integer coding 0:1 and 1:2, with right being the lower number. Purpose: 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. The mean BCVA in decimal notation was 0.970.15 and 0.970.18 with the Snellen and ETDRS charts, respectively (P =0.78). va_methods, [4], The chart was designed by Ian Bailey[5] and Jan E. Lovie-Kitchin at the National Vision Research Institute of Australia. va() will detect the class automatically based on specific rules detailed below. Search for Similar Articles ETDRS letter, in order to keep it as a measurement (not: NA). Accepted VA formats / Plausibility checks Eye endobj myop will work reliably if you adhere to the following: An exception is when there is only one column for each eye. This chart and VA conversion formulas are based on charts in In order to calculate with qualitative entries counting fingers, Must be atomic. Bookshelf ETDRS must be integer-equivalent between 0 and 100 (integer equivalent means, it can also be a character vector), snellendec must be greater than 0 and smaller or equal to 2, Qualitative must be either of PL, LP, NLP, NPL, HM, CF (any case allowed), Any element which is implausible / not recognized will be converted to NA. Am J Ophthalmol. Conclusion: This may then result in a vector of "mixed" VA notations. A conversion to snellen gives a good gauge of how the visual 9 0 obj 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. The formula is subsequently validated with manual conversion by two independent clinicians (CL and TS). Off. Basically the opposite of myop() - a slightly intelligent wrapper around tidyr::pivot_longer() and tidyr::pivot_wider(). Holladay J. See Also 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). Letter Score logMAR Snellen Equivaent 0-3 1.70-1.64 <20/800 4 to 8 1.62-1.54 20/800 9 to 13 1.52-1.44 20/640 14 to 18 1.42-1.34 20/500 11 0 obj The etdrs values for NLP and PL are deliberately set at those values because 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. VA chart 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. Dutch eye doctor Hermann Snellen developed the Snellen eye chart in the 1860s. An official website of the United States government. 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. proposed the line scoring method [3]. However, visual acuity measurements expressed as logMAR units are not intuitively interpretable by clinicians. 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. <> 4 5 The ETDRS charts are now considered as the most accurate and standard method of VA recording, . From the data presented in the current study, a conversion chart was created to aid appreciation of empiric Snellen and ETDRS equivalents compared with theoretic conversion standards . Some error has occurred while processing your request. Visual acuity is a vital outcome measure in determining efficacy of treatments and interventions in ophthalmology. VA conversion reveal() is basically a slightly complicated wrapper around mean(), sd(), length(), min() and max() (with na.rm = TRUE and length() counting only non-NA values). However, you need to be very careful in those cases if resulting data frame is plausible. endobj ## if you only want to rename one or a few columns: #> [1] "patID" "oculus" "eyepressure" "VA", ## information on the tested dimension is included ("iop"), ## VA and eye strings are separated by underscores, #> [1] "id" "surgery_right" "surgery_left" "iop_r_preop", #> [5] "iop_r_postop" "iop_l_preop" "iop_l_postop" "va_r_preop", #> [9] "va_r_postop" "va_l_preop" "va_l_postop", ## Id and Eye are common names, there are no spaces, ## VA is separated from the rest with an underscore, ## There is an unnecessary underscore (etdrs are always letters). 1997;13:38891. entries equivalent to 0.02 logmar. "etdrs", "logmar", "snellen" or "snellendec". If you have different codes, you can change the recognized strings with the eyestrings argument, which needs to be a list. The Snellen visual acuity notation was developed by Hermann Snellen in 1862, during the time of the Civil War. However, additional letters read or missed letters are not accounted for. When using a LogMAR chart, visual acuity is scored with reference to the logarithm of the minimum angle of resolution, as the chart's name suggests. Eye 34, 21482149 (2020). https://doi.org/10.1167/iovs.05-0981. The same outcomes (in Snellen fractions) were obtained with statistical manipulation of either approxETDRS letter scores or logMAR conversions. numeric (for logMAR), or integer (for ETDRS). Snellen are unfortunately often entered with +/-, which is a violation of psychophysical methods designed to assign one (!) endobj See also Examples. 10 0 obj The conversion of Snellen data to logMAR can also be misleading as the abstract and results sections of papers that use this process sometimes give the impression that data have been collected using logMAR charts suggesting the data are more reliable that they actually are. For entries with mixed notation, use va_mixed instead. Either of character (for Snellen, snellendec, and qualitative), - https://doi.org/10.1167/iovs.05-0981, (No) light perception are converted following the suggestions by Accessibility males. (Also see related commentary by Andrew P. Schachat, MD, and Marco A. Zarbin, MD, in the same issue. [1][3] They described their motivation for designing the LogMAR chart as follows: "We have designed a series of near vision charts in which the typeface, size progression, size range, number of words per row and spacings were chosen in an endeavour to achieve a standardization of the test task.". PubMedGoogle Scholar. The mean reading times for the subjects were 34.65 s for ETDRS, 21.17 s for reduced logMAR and 18.67 s for Snellen. To Snellen: eye is dedicated to facilitate ophthalmic research, providing convenient application programming interfaces (API) for common tasks: eye includes a visual acuity conversion chart. TRUE: plus/minus US: 877-225-6101 -- International: 00 1 847 763 0500, US Toll-Free: 877-225-6101 -- International: 00 1 847 763 0500, NEW, from M&S Technologies, the CTS 5.5 Ultra-High Resolution Display for use in ophthalmic researc, M&S Technologies Launches the Smart System Virtual Reality Headset Including Critical Eye Tracking, Dynamic Voice Recognition capability available for M&S Technologies Smart System 2 | 2020. 13 0 obj Normal visual acuity (which is better than 1.0 (20/20) ) is represented by negative logMAR values. For this study, the authors assessed data from 12 prospective clinical trials conducted at a large urban retina practice in the United States. between Snellen (decimal, meter and feet), ETDRS, and logMAR. ## will automatically detect VA class and convert to logMAR by default, ## snellen, mixed with categories. 3,575,655. Therefore, we recommend the following for data entry in excel. A linear relationship exists between true ETDRS letter scores, approxETDRS letter scores, and logMAR units. https://doi.org/10.1038/s41433-021-01764-y, DOI: https://doi.org/10.1038/s41433-021-01764-y. Although kind of nice, blink is more a nerdy extra and is not likely to be used much. snellen_steps, It is more user friendly, since it avoids decimal values and is more intuitive, since higher values indicate better vision. Disclaimer. PubMedGoogle Scholar. To which Snellen notation to convert: "m", "dec" or "ft", how +/- entries are evaluated. Visual Acuity Reporting in Clinical Research Publications. Thus, the authors said, the specific retinal disease state and extent of edema may play a role in the variability between the measurements. Provided by the Springer Nature SharedIt content-sharing initiative, International Journal of Retina and Vitreous (2022), Eye (Eye) va_mixed(), 2010. Novel Method for Analyzing Snellen Visual Acuity Measurements. Retina 30 (7). stream & Tm. ziXyS*(P9_"H3 PznjpPF"?9a{i\[$1&GPwa1W1"82zrX?7C=BH&LBOI"I`RAk}d endobj logMAR to ETDRS: logMAR rounded to the first digit and converted with the visual acuity chart (see section VA chart) Snellen to logMAR: logMAR = -1 * log10(snellen_frac) Snellen to ETDRS: ETDRS = 85 + 50 * log10(snellen_frac) doi: 10.1097/iae.0b013e3181d87e04 ETDRS to logMAR: logMAR = -0.02 * etdrs + 1.7 "etdrs", "logmar" or "snellen" - Gregori, Ninel Z, William Feuer, and Philip J Rosenfeld. and JavaScript. Our data set consists of 100 patients who underwent corneal collagen cross linking. This may be a necessary data formal for specific questions. [1] For this reason, the LogMAR chart is recommended, particularly in a research setting.[2]. Usage Trans Am Ophthalmol Soc. To obtain Br J Ophthalmol. in Snellen. In this case, the argument var will be used to name the resulting variable. It will no longer be. The World Health Organization established criteria for low vision using the LogMAR scale. Entries with mixed VA notations Better just "VA", #> [1] "Id" "Eye" "FollowupDays" "BaselineAge", #> [5] "Gender" "VA_ETDRS_Letters" "InjectionNumber". [in press]. Schulze-Bonsel et al. In the meantime, to ensure continued support, we are displaying the site without styles eyes_to_string() parses the output of eyes into text under the hood. A linear relationship exists . logMAR to ETDRS: logMAR rounded to the first digit and converted with the chart. Google Scholar. 1982;94:916. Qualitative visual acuity entries It is very This, again, requires a certain format of names and codes - See Names and Codes. 1 for an example of our spreadsheet. Any fractions allowed. Article Convert between any of Snellen (meter/ feet/ decimal! This is intended for integration into rmarkdown reports, or for easy copy / pasting. 2023 Jan 30;59(2):263. doi: 10.3390/medicina59020263. <> The authors have no commercial or proprietary interest in any product or corporation mentioned in this article. TRUE: plus/minus E.g., preop instead of pre_op, or simply VA instead of VA_ETDRS_Letters, Thanks to Hadley Wickham and all developers of the. back to Snellen, it is a very natural thing to eye specialists to think https://doi.org/10.1016/j.jcrs.2004.01.014. Each letter has a score value of 0.02 log units. endobj 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). Asia Pac J Ophthalmol (Phila). For counting eyes, eyes need to be coded in commonly used ways. 1) hence reducing risk of transcription errors. The Snellen chart, which dates back to 1862, is also commonly used to estimate visual acuity. By default, numbers smaller than or equal to 12 will be real English, all other numbers will be numbers. HHS Vulnerability Disclosure, Help Results: A linear relationship exists between true ETDRS letter scores, approxETDRS letter scores, and logMAR units. will force to evaluate from which notation to convert - Must be Out of convenience, data is often entered in a wide format: In eye research, there will be often two columns for the same variable, one column for each eye. 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. The notation will be detected automatically and converted to the desired notation. A conversion to snellen gives a good gauge of how the visual We converted all the Snellen visual acuities to logMAR visual acuities. Again, good names and tidy data always help! We measured their. . 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. Holladay, Jack T. 2004. Visual Acuity Measurements. Journal of Cataract and Refractive Surgery 30 (2): 28790. FALSE: If you have columns with VA or IOP that contain only 0 and 1 for example (which is unlikely, but not impossible), you can just set, Getting the new names based on the indices of the columns, Creating a vector of expected new names for the summary after myopization, Do not use numeric coding for eyes in column names, Separate eye and VA and IOP codes with underscores (bcva_l_preop, VA_r, left_va, IOP_re), Dont use underscores when you dont need to: Consider each section divided by an underscore as a relevant characteristic of your variable. You can change the way numbers are converted to english with the english argument. Visual acuity data must be standardized in a logMAR format to allow for statistical analysis [1]. The VAS scale (VAS = Visual Acuity Score) serves the same purpose. Michael Bach. 2014 Sep-Oct;3(5):277-85. doi: 10.1097/APO.0000000000000007. From the laboratory to the clinic. va_mixed(), doi: 10.1016/s0002-9394(02)01825-1Beck et al., and https://doi.org/10.1097/iae.0b013e3181d87e04. Michael Bach. Thank you for visiting nature.com. ), logMAR and ETDRS. This is based on the assumption of 5 optotypes in a row. 11 Confusion 2. A logMAR chart (Logarithm of the Minimum Angle of Resolution) is a chart consisting of rows of letters that is used by ophthalmologists, orthoptists, optometrists, and vision scientists to estimate visual acuity. a specific range (0-100). Mean value for Snellen Visual Acuity was 0.043 and that of ETDRS was 0.02365 LogMAR. https://doi.org/10.1016/s0002-9394(02)01825-1. 8600 Rockville Pike if one of CF, HM, LP, PL, NLP, or NPL: Snellen fractions (meter/ feet) need to be entered as fraction with /. In the clinical setting, there is still a mixed use of Snellen acuity charts and ETDRS acuity charts. Any fractions allowed. In the group of patients, the eyes with the lower visual acuity, and the right eyes of the healthy subjects, were . Three out of 5 optotypes per line had to be correctly identified, while wrong answers were monitored. endobj For more information, please refer to our Privacy Policy. Any element which is implausible/ not recognized will be converted to NA. Character vectors will be omitted (and it should give a warning that it has done so). endobj 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. An important step in eyes is the guessing of the columns that identify patients and eyes. Outcome measures included absolute VA and VA variability among disease states. doi: 10.1016/s0002-9394 (02)01825-1 Hand movements and counting fingers are converted following Schulze-Bonsel et al. 1, 35 The first 4 columns contain VA equivalents as they are currently understood, and the fifth column contains the expected 95% ETDRS CI for each Snellen . Logmar-Snellen Conversion Table. Trabelsi O, Bouladi M, Ouertani A, Trabelsi A. Clin Ophthalmol. All Snellen and ETDRS VA measurements were converted to logMAR units for direct comparison, and the variability between measurements was calculated. Either of character (for Snellen, snellendec, and qualitative), Snellen visual acuity measurements were converted to approximate ETDRS (approxETDRS) letter scores for statistical manipulations and then converted back to Snellen equivalent fractions. Rosser et al. ignoring plus/minus entries and just returning the You can read the full text of this article if you: Keywords All told, 413 patients (773 eyes) met the inclusion criteria for this study. This can compromise data quality and accuracy of outcomes. Other VA converter: similar and uniform legibility of each line and offer an ease of conversion of VA to a logarithmic scale. will force to evaluate from which notation to convert - Must be Eye. See also "VA classes", logMAR to ETDRS: logMAR rounded to the first digit and converted with This calculator is intended as a convenient screener for visual acuity to be used on a mobile device and should not be used as a replacement for in-office testing.Evidence for smartphone apps for Snellen visual acuity is limited, and currently no app has been found to be accurate to within at least one line of formal visual acuity testing (and further validation is required). The ETDRS chart is the chart used most often in clinical research. Donders diagnosed vision problems by asking people to look at a chart on a wall and tell him what they could see. It is very Then the column names can consist of eye strings only. The interconversion between Snellen visual acuity measurements, logMAR units, and approxETDRS letter scores was prepared in a tabular form for easy reference. Excel spreadsheet picture depicting an example of Snellen VA 6/122 and 6/12+2 with their respective logMAR equivalents. [ 7 0 R] Holladay et al.doi: 10.1016/j.jcrs.2004.01.014, Beck et al. However, back-conversion should not be Since 1990, M&S Technologies has served eye care professionals. In ETDRS charts, the Sloan letters are used (Sloan letters are perfectly square approximately equally legible one from another), while the BaileyLovie chart used rectangular (5:4) letters based on the Transport typeface, as set out in British Standard 4274:1968.[1]. Firstly, each letter was scored using linear interpolation. endobj any case allowed. The ETDRS chart is fully accessible on modern computerized vision testing systems, thanks to Dr. Bailey and Dr. Lovies work to create a more accurate chart! To which class to convert. the VA chart are used. 2023 Feb 1;9(1):8. doi: 10.1186/s40942-023-00445-0. As each row grew smaller, the amount of space between each row decreased. In order to calculate with qualitative entries counting fingers, The mean and range of testing times were: ETDRS 34.65 (9.38-80.18) seconds, cRLM 21.17 (5-40) seconds, Snellen 18.67 (3-35.56) seconds. BCVA However, LogMAR is actually a notation of vision loss. Snellen fractions need to be entered with "/". means, it can also be a character vector), Qualitative must be either of PL, LP, NLP, NPL, HM, CF (any case allowed). When I started with R, I found it challenging to rename columns and I found the following methods very helpful: Ive got a data frame with unfortunate names: To rename only specific columns, even if you are not sure about their exact position: For even more methods, I found those two threads on Stackoverflow very helpful: reveal() offers a simple API to show common summary statistics for all numeric columns of your data frame. volume34,pages 21482149 (2020)Cite this article. If the argument smallstep = TRUE, the entries will be converted to logmar values (0.02 logmar for each optotype). See Fig. M&S holds US Patent Numbers 7,354,155; 7,926,948; 8,167,429; 8,419,184; [7] Blindness is defined as a best-corrected visual acuity worse than 1.3 LogMAR. Visual acuity testing. ignoring plus/minus entries and just returning the The formula to convert Snellen visual acuity measurements to approxETDRS letter scores is 85 + 50 log (Snellen fraction), which may be rounded to the nearest letter. hand movement and (no) perception of light, use logMAR ! Conversion tables and calculators exist online which allows for whole Snellen fractions to be converted into logMAR equivalents. Eye eyestr was designed with the use in rmarkdown in mind, most explicitly for the use inline. M]D_*zcP?VpON`7?44N]p+8arMa*\ official website and that any information you provide is encrypted the best experience, we recommend you use a more up to date browser (or turn off compatibility mode in or "", "n/a" or " ". reveal() takes the grouping argument by and it returns vector for atomic vectors or a data frame for lists. All Snellen and ETDRS VA measurements were converted to logMAR units for direct comparison, and the variability between measurements was calculated. Distances between lines were not consistent. The score was further modified by adding/subtracting 0.02 logMAR to converted values for letters correctly/incorrectly identified on previous/next line. logMAR to ETDRS: logMAR rounded to the first digit and converted with the visual acuity chart (see section VA chart) Snellen to logMAR: logMAR = -1 * log10 (snellen_frac) Snellen to ETDRS: ETDRS = 85 + 50 * log10 (snellen_frac) 10.1097/iae.0b013e3181d87e04 ETDRS to logMAR: logMAR = -0.02 * etdrs + 1.7 Beck et al. Snellen to ETDRS: ETDRS = 85 + 50 * log10 (snellen_frac) doi: 10.1097/iae.0b013e3181d87e04 ETDRS to logMAR: logMAR = -0.02 * etdrs + 1.7 Beck et al. Eyes were included if a Snellen VA measurement was performed at the visit preceding the initial trial screening and VA was better than counting fingers. acuity for the patients are. The etdrs values for NLP and PL are deliberately set at those values because
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