I do not assume responsability for your data or analysis. In 1982, the chart was renamed the ETDRS chart as it was recommended to be used in the Early Treatment Diabetic Retinopathy Study (note: the terms ETDRS chart and logMAR chart are not interchangeable logMAR is not a type of chart, but rather a term to describe visual acuity notation. 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. endobj Convert between any of Snellen (meter/ feet/ decimal! You can also decide to simply clean your VA vector with cleanVA(x). Then the column names can consist of eye strings only. In the group of patients, the eyes with the lower visual acuity, and the right eyes of the healthy subjects, were . 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. The authors declare no competing interests. Other VA converter: 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. You don't have permission to access this content. It takes an (atomic) vector with visual acuity entries as the only required argument. a specific range (0-100). 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. Arguments to eyes_to_string are passed via : eyestr will create a string which you can paste into a report. doi: 10.1097/iae.0b013e3181d87e04, ETDRS to logMAR: logMAR = -0.02 * etdrs + 1.7 The https:// ensures that you are connecting to the any case allowed. endstream 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 . However, you need to be very careful in those cases if resulting data frame is plausible. hand movement and (no) perception of light, use logMAR ! vector of va class. Visual acuity testing. 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). entries equivalent to 0.02 logmar. "/". Although there seems to be no good statistical reason to convert We converted all the Snellen visual acuities to logMAR visual acuities. Suprachoroidal injection of triamcinolone acetonide plus intravitreal bevacizumab in diabetic macular edema: a randomized pilot trial. 8,425,040; 8,550,631; 10,244,938; and 10,182,713. means, it can also be a character vector), Qualitative must be either of PL, LP, NLP, NPL, HM, CF (any case allowed). VA Variability: Snellen Versus ETDRS Outcomes Because the standard testing . Their revised chart included the same amount of letters on each line, a standardization of legibility, and equidistant rows, to name just a few adjustments. There is basically a nearly infinite amount of possible combinations of how to enter data, and it is likely that myop will not be able to deal with all of them. Results: 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. 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! Must be atomic. Reference values for these are customizable and can be left as CF, HM, LP and NLP (Appendix S1). Schulze-Bonsel, Kilian, Nicolas Feltgen, Hermann Burau, Lutz Hansen, and Michael Bach. If the argument smallstep = TRUE, the entries will be converted to logmar values (0.02 logmar for each optotype). National Library of Medicine ), logMAR and ETDRS. 2009 Dec;107:311-24. <> may email you for journal alerts and information, but is committed in very weird Snellen values that have no correspondence to common charts. Therefore I decided to stop the work on it. va_methods, 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. In the clinical setting, there is still a mixed use of Snellen acuity charts and ETDRS acuity charts. #> 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. PubMedGoogle Scholar. You can also more globally change recognized codes with set_eye_strings(). to maintaining your privacy and will not share your personal information without the VA chart are used. This is a simple function and should not require much explanation. back to Snellen, it is a very natural thing to eye specialists to think 13 0 obj Efficacy of small-incision lenticule extraction surgery in high astigmatism: A meta-analysis. Schulze-Bonsel et al. increase/decrease Snellen fractions by lines. All Snellen and ETDRS VA measurements were converted to logMAR units for direct comparison, and the variability between measurements was calculated. Kaiser PK. It is very 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). Best Method to Measure Visual Acuity? - American Academy of and JavaScript. <> Gregori et al.doi: 10.1097/iae.0b013e3181d87e04. PDF Visual Acuity Testing Procedures Manual - Jaeb Either of character (for Snellen, snellendec, and qualitative), If there are only eye columns in your data (should actually not happen), myop will create identifiers by row position. The mean BCVA in decimal notation was 0.970.15 and 0.970.18 with the Snellen and ETDRS charts, respectively (P =0.78). [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). Allows conversion of CF, HM, LP and NLP into LogMAR. #> Specify eye column with "eye_col" argument, #> patid sex age avdays_induc ethnicity loaded time injgiven va regimen, #> , #> 1 id_1 m 60-69 28 se_asian TRUE 0 TRUE 0.30 ranibi, #> 2 id_1 m 60-69 28 se_asian TRUE 28 TRUE 0.30 ranibi, #> 3 id_1 m 60-69 28 se_asian TRUE 56 TRUE 0.30 ranibi, #> 4 id_1 m 60-69 28 se_asian TRUE 91 TRUE 0.40 ranibi, #> 5 id_1 m 60-69 28 se_asian TRUE 131 TRUE 0.46 ranibi, #> 6 id_1 m 60-69 28 se_asian TRUE 173 TRUE 0.40 ranibi, #> 7 id_1 m 60-69 28 se_asian TRUE 236 TRUE 0.50 ranibi, #> 8 id_1 m 60-69 28 se_asian TRUE 278 TRUE 0.50 ranibi, #> 9 id_1 m 60-69 28 se_asian TRUE 411 TRUE 0.60 ranibi, #> 10 id_1 m 60-69 28 se_asian TRUE 453 TRUE 0.54 ranibi, #> # with 118,245 more rows, and 1 more variable: pre2013 , #> [1] "name" "oculus" "eyepressure" "vision". Would you like email updates of new search results? 2cgSgU - Google Groups va_mixed(), . doi: 10.1097/iae.0b013e3181d87e04, ETDRS to logMAR: logMAR = -0.02 * etdrs + 1.7 The Snellen visual acuity notation was developed by Hermann Snellen in 1862, during the time of the Civil War. 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. 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. o$eP.2F-F}G~fLhIHEoCZwByF9TIW&NM].aBM'?l!]Rh&Jlvg=` A-=x3=C;i{K!ggHIww#+ y"coI i Pl".a]:9!S"8`[0+e)]0TX jtv`wlox\6[Tp)A::"C|(C=g"qy#HUh.=_d#.J]{i\1/BRgiEiFef{zQZzKJ3bP>[#U} r@O8;[zt-)EP=lkC,y}rwvHc'KPRS qc+Hqm EX_+|IpE#l iYi6X"N{p0#!OPBV?#',pWE#>I>][BdMG?=Awr,3A.~Ji(Oi([it5x\S$(;aO=}QQ##Llq6C=> By default, plus/minus entries are evaluated as intended by the The test-retest variability of the charts was similar, with the 95% tolerance limit for change being +/-0.14 logMAR for ETDRS, +/-0.16 for reduced logMAR and +/-0.18 for Snellen. 2023 Feb 8;17:515-525. doi: 10.2147/OPTH.S400156. eCollection 2023. 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. This, again, requires a certain format of names and codes - See Names and Codes. 2009;107:31124. Therefore, we recommend the following for data entry in excel. This chart and VA conversion formulas are based on charts in However, eye is also variable (a dimension of your observation), and it can also be stored in a separate column. 2010 Mar;30(2):200-3. doi: 10.1111/j.1475-1313.2009.00700.x. Holladay, Jack T. 2004. Visual Acuity Measurements. Journal of Cataract and Refractive Surgery 30 (2): 28790. they are unlikely to happen by chance as a wrong entry (and as integers), But remember to put the strings for right eyes first, or pass a named list. It will no longer be. Wolters Kluwer Health males. Google Scholar. volume36,page 1708 (2022)Cite this article, This is a preview of subscription content, access via your institution, Receive 18 print issues and online access, Get just this article for as long as you need it, Prices may be subject to local taxes which are calculated during checkout. https://doi.org/10.1016/j.jcrs.2004.01.014. The Apple iPod Touch (Figure 2), communicating with the EVA PC via Wi-Fi, provides . in very weird Snellen values that have no correspondence to common charts. ETDRS charts (within about 2% of the letter size at each logMAR level). The cols argument takes a tidyselection. Google Scholar. Michael Bach. A linear relationship exists . See Fig. The arguments id and eye arguments overrule the name guessing for the respective columns. Visual Acuity - SPIE which_va(). 5715 W. Howard Street, Niles, IL, 60714 USA Prospective evaluation of visual acuity assessment: a comparison of snellen versus ETDRS charts in clinical practice (An AOS Thesis). You can capitalise the first number with the caps argument. a specific range (0-100). notation. 19 0 obj It will be left in the package as such. Visual Acuity Variability: Comparing Discrepancies between Snellen and Christina Lim. Excel spreadsheet picture depicting an example of Snellen VA 6/122 and 6/12+2 with their respective logMAR equivalents. These conversions were done via our excel spreadsheet formula taking into account methods from our literature searches. eyes recognizes integer coding 0:1 and 1:2, with right being the lower number. Charts with the Snellen E and the Landolt C (Precision Vision) which mimic the ETDRS charts were used to assess visual acuity. 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. 9 0 obj Indeed, in my experience R often needs eyes to be in a single column, with each other variable having their own dedicated column. [Repeatability and reliability of the visual acuity examination on logMAR ETDRS and Snellen chart]. Better just "VA", #> [1] "Id" "Eye" "FollowupDays" "BaselineAge", #> [5] "Gender" "VA_ETDRS_Letters" "InjectionNumber". numeric (for logMAR), or integer (for ETDRS). It uses an S3 generic under the hood with methods for atomic vectors, data frames, and lists of either atomic vectors or data frames. RR.2 Reference Tables For Equivalent Visual Acuity Notations - DICOM equivalent to 0.02 logmar (assuming 5 letters in a row in a chart), NA is assigned to strings such as "." endobj 2010. Novel Method for Analyzing Snellen Visual Acuity Measurements. Retina 30 (7). The formula to convert Snellen visual acuity measurements to approxETDRS letter scores is 85 + 50 log (Snellen fraction), which may be rounded to . Comparison of the ETDRS logMAR, 'compact reduced logMar' and Snellen To help those who are using the standard Snellen chart in their practice and wish to convert it to LogMAR, we have produced 81 possible combinations of Snellen visual acuity and their true. https://doi.org/10.1097/iae.0b013e3181d87e04. endobj In the era of big data, there needs to be an efficient way of tidying up data to facilitate analysis. CAS VA classes The authors declare that they have no conflict of interest. <>/ProcSet[/PDF/Text/ImageB/ImageC/ImageI] >>/MediaBox[ 0 0 612 792] /Contents 4 0 R/Group<>/Tabs/S/StructParents 0>> endobj This overrides the smallstep argument. va_mixed(), If NULL (default), will simply "clean up" VA entries. Accepted VA formats / Plausibility checks P30 EY014801/EY/NEI NIH HHS/United States. <> sharing sensitive information, make sure youre on a federal difficult to justify a "negative" letter score in a test which only has . ## But which dimension of "r"/"l" are we exactly looking at? unambiguous value to visual acuity, with non-arbitrary thresholds based on psychometric functions. It is more user friendly, since it avoids decimal values and is more intuitive, since higher values indicate better vision. endobj plausibility_methods, "etdrs", "logmar", "snellen" or "snellendec". logMAR to ETDRS: logMAR rounded to the first digit and converted with the chart. This site needs JavaScript to work properly. Supported by an unrestricted grant from Research to Prevent Blindness, Inc. and National Eye Institute core center grant P30 EY014801 to the University of Miami. The Bailey-Lovie chart was also designed to be scored in logMAR units, making it easier to convert results based upon various viewing distances. The ETDRS chart is the chart used most often in clinical research. Holladay et al.doi: 10.1016/j.jcrs.2004.01.014, Beck et al. The interconversion between Snellen visual acuity measurements, logMAR units, and approxETDRS letter scores was prepared in a tabular form for easy reference. 10.1016/s0002-9394 (02)01825-1 2020;43:21489. VAwrapper, If smallstep = TRUE, each snellen optotype will be considered Both accept tidyselection. PubMed Central Could be etdrs, logmar, snellendec. 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. Eye 34, 21482149 (2020). J Refractive Surg. 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. Short-Term Total Tamponade with Perfluorocarbon Liquid and Silicone Oil in Complex Rhegmatogenous Retinal Detachment with Severe Proliferative Vitreoretinopathy. ## 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). You can change the way numbers are converted to english with the english argument. 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. Federal government websites often end in .gov or .mil. According to The New York Times, he asked Dr. Snellen to make the chart. test design: Snellen fractions increase/decrease only by lines. your express consent. <> Asia Pac J Ophthalmol (Phila). Visual acuity is a vital outcome measure in determining efficacy of treatments and interventions in ophthalmology. To obtain VA conversion 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. Some error has occurred while processing your request. Bailey IL, Lovie JE (2013). The .gov means its official. You have full access to this article via your institution. HHS Vulnerability Disclosure, Help Trans Am Ophthalmol Soc. Lim, C., De Silva, I. Publishers note Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations. BCVA Conversions Between Letter, LogMAR, and Snellen Visual Acuity Scores Cleans and converts visual acuity notations (classes) All told, 413 patients (773 eyes) met the inclusion criteria for this study. If you have different codes, you can change the recognized strings with the eyestrings argument, which needs to be a list. ignoring plus/minus entries and just returning the Am J Ophthalmol. Please always keep a critical mind when working with data - if you do get results that seem implausible, there may be a chance that the data is in an unfortunate shape for which eye may not be suitable. The ESV-3000 is designed specifically for clinical trials where large-format ETDRS testing (up to 20/200) is performed at 4 meters. Please enable scripts and reload this page. Visual Acuity Testing - University of Iowa Again, good names and tidy data always help! [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.". We measured their. numeric (for logMAR), or integer (for ETDRS). It will remove duplicate rows, and pivot the eye variable to one column and generate a single column for each variable, thus shaping the data for specific types of analysis. Prospective evaluation of visual acuity assessment: a comparison of snellen versus ETDRS charts in clinical practice (An AOS Thesis). You may search for similar articles that contain these same keywords or you may back to Snellen, it is a very natural thing to eye specialists to think 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 . between Snellen (decimal, meter and feet), ETDRS, and logMAR. Thank you for visiting nature.com. 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 Pesky visual acuity notations are now a matter of the past. 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. To which Snellen notation to convert: "m", "dec" or "ft", how +/- entries are evaluated. Ignored if the value should not be plausible. and it has internal reasons that make conversion easier. 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. The ESV-3000 is the only large-format standardized ETDRS testing device. The cluster of optotypes as row space decreased would produce the crowding phenomenon, which has been shown to cause inaccurate acuity measurements. Article Rosser et al. acuity for the patients are. Table: Different notations of visual acuity values as decimal values, Snellen fractions, MAR and LogMAR. VA cleaning Cleans and converts visual acuity notations (classes) 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. 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. doi: 10.1016/s0002-9394(02)01825-1Beck et al., and FOIA Any fractions allowed. I personally find starts_with, ends_with, contains() or the more general matches() very useful. Either of character (for Snellen, snellendec, and qualitative), 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 basic principle of tidy data is: one column for each dimension and one row for each observation. Novel method for analyzing snellen visual acuity measurements Visual acuity data must be standardized in a logMAR format to allow for statistical analysis [1]. The interconversion between Snellen visual acuity measurements, logMAR units, and approxETDRS letter scores was prepared in a tabular form for easy reference. It is very Eye 36, 1708 (2022). The same outcomes (in Snellen fractions) were obtained with statistical manipulation of either approxETDRS letter scores or logMAR conversions. ## 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. You can read the full text of this article if you: Keywords Therefore, Snellen matching the nearest ETDRS and logMAR value in Accessibility endobj You can get creative with your snellens. A linear relationship exists between true ETDRS letter scores, approxETDRS letter scores, and logMAR units. Arguments 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 <> Ferris FL, Kassoff A, Bresnick GH, Bailey I. Factors Contributing to Discrepancy Between Visual Acuity Fractions Derived From a Snellen Chart and Letter Scores on the Early Treatment Diabetic Retinopathy Study Chart. Usage ?myop for help, #> From etdrs. 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). E.g., preop instead of pre_op, or simply VA instead of VA_ETDRS_Letters, Thanks to Hadley Wickham and all developers of the. official website and that any information you provide is encrypted notation for qualitative entries is simplified. %PDF-1.5 snellen_steps, Any element which is implausible/ not recognized will be converted to NA. For counting eyes, eyes need to be coded in commonly used ways. Snellen fractions (meter/ feet) need to be entered as fraction with Front Med (Lausanne). VA chart The authors have no commercial or proprietary interest in any product or corporation mentioned in this article. The mean difference was 1 letter (0.0195 LogMAR) better on ETDRS chart when compared to Snellen chart. Although kind of nice, blink is more a nerdy extra and is not likely to be used much. ISSN 1476-5454 (online) endobj TRUE: plus/minus More recently, the LogMAR chart has been introduced into clinical practice. However, visual acuity measurements expressed as logMAR units are not intuitively interpretable by clinicians. the VA chart are used. BCVA Careers. An important step in eyes is the guessing of the columns that identify patients and eyes. & Tm. ziXyS*(P9_"H3 PznjpPF"?9a{i\[$1&GPwa1W1"82zrX?7C=BH&LBOI"I`RAk}d Search for Similar Articles Thank you for visiting nature.com. 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. This overrides the smallstep argument. 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. difficult to justify a "negative" letter score in a test which only has 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. The same outcomes (in Snellen fractions) were obtained with statistical manipulation of either approxETDRS letter scores or logMAR conversions. 2001;85:4326. For more information, please refer to our Privacy Policy. In a retrospective chart review, Yu et al. 11 Confusion 2. Notation for qualitative entries is simplified (NPL becomes NLP, PL becomes LP). #> id eye surgery iop_preop iop_postop va_preop va_postop, #> , #> 1 a right TE 21 11 41 45, #> 2 a left TE 31 11 41 45, #> 3 b right TE 22 12 42 46, #> 4 b left TE 32 12 42 46, #> 5 c right SLT 23 13 43 47, #> 6 c left TE 33 13 43 47, #> 7 d right SLT 24 14 44 48, #> 8 d left SLT 34 14 44 48, #> id surgery r_iop_preop r_iop_postop r_va_preop r_va_postop l_iop_preop, #> , #> 1 a TE 21 11 41 45 31, #> 2 b TE 22 12 42 46 32, #> 3 c SLT 23 13 43 47 , #> 4 c TE 33, #> 5 d SLT 24 14 44 48 34.