Visual Acuity Testing Procedures
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1. e Room lighting should remain at the level of normal visual acuity testing dim incandescent lighting The trial frame should be removed and the subject should close the opposite eye and occlude it by making a tight seal with the palm around the orbit and the bridge of the nose e The indirect ophthalmoscope light should be in focus at three feet and the rheostat set at six volts From a distance of three feet the beam should be directed in and out of the eye at least four times the subject should be asked to respond when he she sees the light If the examiner is convinced that the subject perceives the light vision should be recorded as light perception otherwise as no light perception RVACC Visual Acuity Testing Procedures Manual_2013 10 17 docx Page 9 of 12 CHAPTER 2 STANDARD ETDRS VISUAL ACUITY PROTOCOL The Standard ETDRS Visual Acuity Protocol should only be used as a back up in the event the Electronic Visual Acuity Tester EVA is not functioning if your site has ETDRS equipment and is ETDRS certified A Visual Acuity Chart Modified Bailey Lovie The ETDRS visual acuity charts 1 and 2 are used for standardized measurement of visual acuity Acuity testing of all subjects regardless of visual acuity begins at four meters Two ETDRS Visual Acuity Charts are used for the measurement of visual acuity each with a different letter sequence The right eye will always be tested with Chart 1 and the left eye with Chart 2 B Ill2. a study was conducted in which high validity and test retest reliability were demonstrated Moke PS Turpin AH Beck RW etal A computerized method of visual acuity testing Adaptation of the amblyopia treatment study visual acuity testing protocol Am J Ophthalmol 2001 132 903 14 1 Overview of E ETDRS Visual Acuity Testing Protocol In brief the E ETDRS Visual Acuity Testing Protocol consists of an initial screening phase to obtain an approximation of the visual acuity threshold and then a testing phase to obtain the visual acuity score The protocol is summarized below The complete algorithm is depicted in the figure that follows RVACC Visual Acuity Testing Procedures Manual_2013 10 17 docx Page 5 of 12 Electronic ETDRS E ETDRS Visual Acuity Testing Protocol Overview The E ETDRS testing protocol e Screening phase With single letter presentations determines smallest logMAR level at which a letter is correctly identified e Testing phase Starts testing letters by intermixing letter sizes of screening phase score and one level smaller e Test progress If a letter is missed at a level one level larger is added to the testing mix if a letter is correct at a level one level smaller is added to the testing mix e Acuity determination Tests 5 letters at each level until smallest level with 5 5 correct and the smallest level with 0 5 correct are determined IN THE FOLLOWING EXAMPLE C CORRECT AND M MIS
3. 11 of 12 e If no letters are read correctly at either the four meter distance or the one meter distance the visual acuity score is 0 and testing for light perception should be performed as described in Chapter 1 Section C Poor Vision Testing Testing for Light Perception RVACC Visual Acuity Testing Procedures Manual_2013 10 17 docx Page 12 of 12
4. be refracted at four meters In addition to the occluder in the trial frame the left eye is occluded with an eye patch or pad placed beneath the trial frame With the lens correction obtained by subjective refraction in the trial frame the subject is asked to read ETDRS Visual Acuity Chart 1 from the top with the right eye It is emphasized to the subject that each answer will be scored so adequate time should be allowed for each letter in order to achieve the best identification The subject is instructed that all of the figures to be read are letters and that there are no numbers The examiner records each letter identified correctly by the subject as he she reads the chart by circling the corresponding letter on the ETDRS score sheet or study form Letters read incorrectly or for which no guesses are made are not marked on this form Each letter read correctly is scored as one point The score for each line including zero if no letters were read correctly on that line and the total score for the eye are recorded on the form as soon as the four meter testing has been completed If the number of letters read correctly at four meters is less than twenty the test should be repeated at one meter and both the four meter and one meter totals should be recorded on the ETDRS score sheet or study form Both eyes should be tested at four meters before the subject is moved up to the one meter test distance It is strongly advised that the total number
5. is shown at each logMAR level Show 20 400 letter Incorrect Correct 20 12 Show letters in 3 level steps e g 20 200 Show letter at each Show a 20 800 20 100 20 50 20 25 20 12 until either a 20 400__ successively smaller Hsin Oe miss or 20 12 correct Correct level until either a miss Correct or 20 400 correct Letter missed Show letter 2 levels up from missed level i e level smaller than last correct level Incorrect Letter Incorrect Correct Missed Show letter at each successive Show letter at each successively larger level until correct smaller level until a miss or 20 12 response or 20 800 is shown correct Screening score is Screeni is last t level creening score 1S last correct leve 20 800 or 20 800 if last letter shown is 20 800 Threshold Phase To start the letter pool consists of letters from 2 levels the level of screening phase score and one level smaller Each letter presentation is randomly selected from the active pool of letters with the stipulation that the first letter and every third letter must be from the largest level in active letter pool A level remains in the active pool until 5 letters are tested at the level A new level is added to the active letter pool when a A letter from largest level in the pool is missed one level larger is added to letter poolt b A letter from smallest level in the pool is correct one level smaller is added to let
6. SED Example Screening 20 400c 20 200c 20 100c 20 50c 20 25m 20 40m Score 20 50 Test progress 1 Start by intermixing 20 50 and 20 40 letters 20 50c 20 40m 20 50c 20 40m 20 50m 2 Because a 20 50 letter was missed add 20 63 to the letter mix so now will have letters of 20 40 20 50 and 20 63 intermixed 20 63c 20 50c 20 40c 3 Because 20 40 was correct add 20 32 to the letter mix mix is now 20 32 20 40 20 50 and 20 63 20 32m 20 63c 20 63c 20 50m 4 Five letters at 20 50 have been tested so it drops out of the mix mix is now 20 32 20 40 and 20 63 20 63c 20 40c 20 32m 20 40m 5 Five letters at 20 40 have been tested so it drops out of the mix mix is now 20 32 and 20 63 20 32m 20 32m 20 63c 6 Five letters at 20 63 have been tested so it drops out of the mix mix is now 20 32 only 20 32m 7 Five letters at 20 32 have been tested there are no letters left in the mix so test is over Test summary 20 63 5 5 correct 20 50 3 5 correct 20 40 2 5 correct 20 32 0 5 correct Letter Score 10 number of letters correctly identified 55 5 times the number of lines above larger than 20 63 and through 20 800 65 Snellen Notation logMAR to Snellen conversion for 65 letters 20 50 RVACC Visual Acuity Testing Procedures Manual_2013 10 17 docx Page 6 of 12 Electronic ETDRS E ETDRS Visual Acuity Testing Protocol Algorithm Screening Phase In each step one letter
7. Visual Acuity Testing Procedures Manual Version 1 4 Revised October 2013 RVACC Visual Acuity Testing Procedures Manual_2013 10 17 docx Table of Contents CHAPTER 1 VISUAL ACUITY TESTING USING THE EVA SYSTEM 3 Aw lt El ctronic Visual Acuity TEStetycie iectesaeciamcsncesuts deeds teenacinnrsoenes eeeeantoedeeey Qivoaatennodaaclaeancees 3 EVA System Description Current Models ceceecessseesseeceseeesecseeeeeaeecsaecsseessneeenees 3 EVA System Description Legacy Models eee eeeecssseeesceesseceseeeseeeeneecnaeenseeeseeeenees 4 System Calibration r EA E E E aaah aon eae 4 B E ETDRS Testing Protocol iiss sssccdecscedaati seine i i A RER ness a EA 5 Overview of E ETDRS Visual Acuity Testing Protocol seesssseesseessesssereseeeesseessee 5 Visual Acuity Testing Procedures j2 25cutiantn aoaee cecilia ance iis 8 Sale Guards tO AVO d E aS ae ran a a A E A E A bans aes 9 C Poor Vision Testing Testing Light Perception sssssesssesssssesssressressessserssseessseesseesseessee 9 CHAPTER 2 STANDARD ETDRS VISUAL ACUITY PROTOCOL 10 A Visual Acuity Chart Modified Bailey Lovie cece esecsseceseeeseeeeseeceaeceseeeseeeeaeecsaeens 10 B Illumination of Visual Acuity Charts and ROOM ecceeseeceeseeceeeeeceeeeeceeneeceeeeeenteeeesaes 10 C Maintenance of ETDRS Visual Acuity Charts and ROOM ceecceceeseceeeeeceeeeeeeteeeeeaes 10 D Best Corrected Visual Acuity Measurementt
8. e suggested that the subject fixate eccentrically or turn or move his her head from side to side or up and down if this improves visual acuity If the subject employs these maneuvers care must be taken to ensure that the fellow eye remains covered When the subject cannot read a letter he she is told to guess If the subject states that a letter is one of two letters then he she is asked to choose only one letter and if necessary to guess When the subject gives one response but then gives a second response before the first response has been finalized i e before the technician has verified the response as correct or incorrect and before the letter presentation on the EVA screen changes the subject should be asked if that is his her final answer if the subject equivocates ask the subject to choose one letter Once the technician has verified the response and the letter presentation has changed on the EVA no changes can be made in the subject s response If the subject provides a number or any other response other than one of the 26 letters of the alphabet the subject should be told again that there are only letters on the chart and to respond with a letter C Poor Vision Testing Testing Light Perception If the subject cannot identify any letters on visual acuity testing of an eye i e letter score 0 the eye is tested for light perception with the indirect ophthalmoscope as the light source The following procedure is required
9. ecssccesscecessceceseeeceeececeeeeecseeeeeseeeeesaes 11 IB POOR Y tS Mott AT sue OE cay EE cy accua EE E TE E 11 F Calculating the Visual Acuity SCOre i scc asdcies sets docoseydehavaavsvassivs hes duehesvategetastntecauiavennes 11 RVACC Visual Acuity Testing Procedures Manual_2013 10 17 docx Page 2 of 12 CHAPTER 1 VISUAL ACUITY TESTING USING THE EVA SYSTEM It is essential to have standardized visual acuity measurements for each examination at each of the participating clinics to minimize the effects of acuity examiner and subject bias Visual acuity testing is performed with the Electronic Visual Acuity Tester EVA using a protocol called the Electronic ETDRS E ETDRS Visual Acuity Testing Protocol This protocol has been developed to provide a visual acuity score that is comparable to that using the manual testing protocol used in the Early Treatment Diabetic Retinopathy Study ETDRS The ETDRS chart testing is used as a back up in case the EVA is not functioning if your site has ETDRS equipment and is ETDRS certified Visual acuity measurements for each eye are obtained by a certified visual acuity examiner after refraction and before the subject s pupils have been dilated A Electronic Visual Acuity Tester 1 EVA System Description Current Models The most recent EVA Figure 1 systems use an Apple iPod Touch that communicates with a personal computer running a Windows 7 operating system For normal high contrast testing st
10. imuli are high contrast black letters with luminance of at least 95 candelas meter and contrast of 98 The system can present single letters or lines of letters Single letter testing is used in the Electronic ETDRS program whereas lines of letters can be used for refraction Single letters are framed with crowding bars spaced one letter width around the letter For low contrast testing only on Model 12 WIN EVA Testers stimuli are gray letters with a contrast of either 2 5 or 5 compared to the white background Letters are framed with crowding bars of the same contrast For lines of letters up to five letters are displayed with a decreasing number of letters per line as letter size increases With a high resolution 1920x1080 21 5 or 23 6 inch monitor the system is capable of displaying letters from 20 800 1 6 logMAR to 20 6 0 5 logMAR at a test distance of 3 meters Letter size is a close but not exact approximation of the logMAR progression of the ETDRS charts within about 2 of the letter size at each logMAR level The Apple iPod Touch Figure 2 communicating with the EVA PC via Wi Fi provides instructions for the technician allows entry of identification data displays the letter that is being shown on the monitor records the responses and sends instructions to the EVA PC with regard to the sequence of letter presentations The size of each letter presentation is determined by a computer program based on the subject s resp
11. of letters correctly read at four meters be calculated as soon as the four meter testing has been concluded in order to identify subjects who require 1 meter testing Prior to actual testing at one meter 0 75 D sphere should be added to the correction already in the trial frame to compensate for the new distance The subject must sit for testing at the one meter distance The same procedure for obtaining visual acuity for the right eye is used for the left eye except that ETDRS Visual Acuity Chart 2 is used Chart 1 should never be exposed to the left eye and chart 2 should never be exposed to the right eye even when switching charts and occlusion E Poor Vision Testing Follow the procedures described in Chapter 1 Section C Poor Vision Testing Testing for Light Perception F Calculating the Visual Acuity Score After each measurement of visual acuity the visual acuity score for the visit is calculated The visual acuity score is defined as follows e If twenty or more letters are read correctly at the four meter test distance the visual acuity score is equal to the number of letters N read correctly at four meters 30 If one or more but less than twenty letters are read correctly at four meter distance the visual acuity score is equal to the number of letters read correctly at four meters plus the number of letters read correctly at one meter in the first six lines RVACC Visual Acuity Testing Procedures Manual_2013 10 17 docx Page
12. onses RVACC Visual Acuity Testing Procedures Manual_2013 10 17 docx Page 3 of 12 2 EVA System Description Legacy Models The EVA Figure 3 utilizes a programmed Palm handheld device that communicates with a personal computer running a Linux or Windows XP operating system Stimuli are high contrast black and white letters with luminance of 85 to 105 candelas meter and contrast of 98 The system can present single letters or lines of letters Single letter testing is used in the Electronic ETDRS program whereas lines of letters can be used for refraction Single letters are framed with crowding bars spaced one letter width around the letter For lines of letters five letters are displayed for sizes smaller than 20 160 on models prior to July 2008 and smaller than 20 200 after July 2008 a decreasing number of letters is displayed as letter size increases With a high resolution 1600x1200 17 inch monitor the system is capable of displaying letters from 20 800 1 6 logMAR to 20 12 5 0 2 logMAR at a test distance of 3 meters With a 19 LCD monitor at 1280x800 models since July 2007 the system displays a range from 20 800 1 6 logMAR to 20 10 0 3 logMAR at a test distance of 3 meters Letter size is a close but not exact approximation of the logMAR progression of the ETDRS charts within about 2 of the letter size at each logMAR level The Palm handheld device Figure 4 communicating with the EVA through a connec
13. rds the back of the light box If the aluminum sleeves are discarded they must be replaced See ordering information at the end of this section Furthermore when changing the fluorescent light tubes the new tubes must be burned in i e left on continuously for 96 hours before using the ETDRS light box To maintain the ETDRS charts in good condition vision examiners are advised to slide the charts into the front slot of the light box rather than bending the charts when changing charts in the front compartment of the light box To maintain the high contrast of the white background the ETDRS charts examiners should refrain from touching the front of the charts with their fingers pens pencils etc If the ETDRS charts become permanently damaged or yellowed they should be replaced The ETDRS vision testing equipment illuminator cabinet floor stand with casters Original Series ETDRS charts and replacement tubes with aluminum sleeves can be ordered from Precision Vision 944 First Avenue La Salle IL 61301 800 772 9211 phone and 800 223 2224 fax RVACC Visual Acuity Testing Procedures Manual_2013 10 17 docx Page 10 of 12 D Best Corrected Visual Acuity Measurements The right eye is tested first and then the left eye The subject is seated such that the distance from the outer canthus of the subject s eye to the ETDRS Visual Acuity Chart is 4 0 meters This testing distance is always used first even if the subject could not
14. t e Verify testing distance from EVA to the front of the patient s face is 3 meters 118 inches e Turn on Apple iPod Touch OR Palm and remove stylus Study Subject Testing e On main menu tap E ETDRS icon e Follow instructions on Apple iPod Touch or Palm Shut Down System e Turn off the PC tester by selecting Shutdown icon on main menu OR Briefly press and release the power button on the EVA tower 2 Visual Acuity Testing Procedures a Trial frames are to be used for refractive correction In addition to the occluder in the trial frame for testing the right eye left eye is occluded with an eye patch or pad placed beneath the trial frames and vice versa b If the protocol specifies that both eyes are to be tested the right eye is always tested first c Visual acuity testing is to be done without cycloplegia and without pupil dilation RVACC Visual Acuity Testing Procedures Manual_2013 10 17 docx Page 8 of 12 3 Safeguards to Avoid Bias The examiner will be masked to prior visual acuity scores when feasible for a study Due to the automated nature of the computerized EVA testing the potential for induction of bias on the part of the technician is minimized Technician instructions to the subject are to be minimal a The subject should be told that there are only letters and no numbers and that each letter is bracketed by lines on all four sides For subjects with poor central vision it may b
15. ted cable or wirelessly with Bluetooth provides instructions for the technician allows entry of identification data displays the letter that is being shown on the monitor records the responses and sends instructions to the EVA with regard to the sequence of letter presentations The size of each letter presentation is determined by a computer program based on the subject s responses 3 System Calibration Two system calibrations are performed at regular intervals 1 size calibration to confirm letters are displayed accurately and 2 luminance calibration to confirm the monitor screen is sufficiently bright for testing Size calibration must be performed at each study visit For non study use size calibration is recommended at least quarterly Luminance calibration must be performed at each study visit Refer to the EVA User s Manual for instructions specific to your EVA Model monitor and RVACC Visual Acuity Testing Procedures Manual_2013 10 17 docx Page 4 of 12 light meter EVA User s Manuals can be found on the EVA website http eva jaeb org and find your model under the Documents tab B E ETDRS Testing Protocol The EVA runs a visual acuity testing program called E ETDRS which stands for Electronic Early Treatment Diabetic Retinopathy Study The program has been developed to provide a visual acuity letter score that is comparable to the ETDRS chart testing score As part of the development of the E ETDRS protocol
16. ter pool Testing continues until an upper logMAR level with 5 of 5 letters correct and a lower logMAR level with 0 of 5 letters correct are determined and 5 letters are tested on all levels in between upper and lower logMAR levels Visual acuity score is the number of letters correctly identified during threshold testing plus 5 letters for each logMAR line above the upper logMAR level through 20 800 NOTE EVA Models released after July 2008 6 WRH and above include a 20 10 letter size The smallest size on models prior to July 2008 is 20 12 The screening phase uses the letters V R K and D The threshold phase uses the same 5 letters from the Sloan letter set that appear on the original ETDRS charts for right and left eyes Unless screening score was 20 12 in which case letter pool consists of only 20 12 level letters Models with 20 10 include both 20 12 and 20 10 in letter pool Unless 20 800 letter is missed Unless 20 12 is correct 20 10 on newer models If 20 12 20 10 on newer models becomes part of the active letter pool it will be the lower logMAR level RVACC Visual Acuity Testing Procedures Manual_2013 10 17 docx Page 7 of 12 Testing Procedures Using the EVA Before each subject study visit Calibrate monitor for letter size Check monitor luminance Check room lighting level dim incandescent lighting is recommended fluorescent lighting should not be used no glare on screen no spotlights Before Every Tes
17. umination of Visual Acuity Charts and Room If required by study protocol each clinic will have use an ETDRS light box for the ETDRS visual acuity charts during any study acuity testing if the EVA is non functional The light box should be hung on the wall or placed on a stand that can be purchased from the Lighthouse for the Blind in New York at a height such that the top of the 3 row of letters 0 8 LogMAR is 49 2 inches 124 5 5 1 cm from the floor Room lighting should be between 50 100 foot candles of light and should be uniform between the subject and the light box Room lighting should be measured using a light meter placed on the white background of one of the ETDRS charts that is inserted into the front of the non illuminated light box The distance from the outer canthus of the subject s eye to the front of the ETDRS chart should be 4 0 meters and should be measured with a tape measure tautly held or a rigid measuring stick C Maintenance of ETDRS Visual Acuity Charts and Room The two 20 watt Cool Daylight fluorescent tubes in the ETDRS light box must be changed annually and a sticker affixed to the side or back of the light box with the date that the bulbs were changed Twenty watt Cool Daylight fluorescent tubes can be purchased from a local hardware store When changing the fluorescent tubes the aluminum fenestrated sleeves must be saved and centered on the new light tubes with the opening of the sleeves pointing towa
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