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Visual Acuity and Evidence-Based Medicine

Visual Acuity and Evidence-Based Medicine. A Failure in Knowledge Translation?. Sound Bites of 2008. Knowledge Translation Knowledge Exchange Knowledge Synthesis Evidence-Based Medicine Best Practice. The Parties Involved…. Researchers Clinicians Students Policy Makers / Politicians

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Visual Acuity and Evidence-Based Medicine

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  1. Visual Acuity and Evidence-Based Medicine A Failure in Knowledge Translation?

  2. Sound Bites of 2008 • Knowledge Translation • Knowledge Exchange • Knowledge Synthesis • Evidence-Based Medicine • Best Practice

  3. The Parties Involved… • Researchers • Clinicians • Students • Policy Makers / Politicians • Administrators • Funding Agencies • Industry…

  4. An Example of “Best Practice” in Action – Visual Acuity

  5. Why measure VA? • Refraction - Presbyopia • Clinical tool • Impairment benefits • Policy Guidelines • Driving License / Personal/Commercial • Airplane License / Personal/Commercial • Etc.

  6. Historical Dates of Relevance • Initial Ideas about measuring resolution of the eye: Ancient Egypt • Resolve Mizar and Alkor (Big Dipper) as separate stars • Later refined: Need 30 sec of visual arc to resolve stars (Hooke, 17th Century)

  7. Beginning of KT • 1843: Küchler (ophthalmologist) calls for standardized vision testing • Jäger, Stellwagen von Cairon, Donders & Snellen develop ideas • 1862: Snellen publishes his chart design

  8. Snellen’s originals

  9. How to improve the original? • 1886: Green • Sans serif letters, geometric size progression, equal target number

  10. Recognition versus Resolution • 1904: Landolt • Landolt-Rings: advantages Then 71 years of silence: Two world wars

  11. Optotypes

  12. How to improve the original? • 1952: Sloan • Standardized Letters • 1976: Bailey & Lovie • Logarhythmic size progression, equal target number, letter-by-letter scoring (see 1886 Green)

  13. How to improve the original? • 1982: Ferris et al. • Early Treatment for Diabetic Retinopathy Study (ETDRS) • OD OS OU

  14. Improvements Continue • Sheedy et al. 1984 • Optimal luminance parameters • Retro-illumination (Lighthouse) • Holladay, 1991 • Log MAR for statistics

  15. ETDRS • Gold Standard since 1993 • Mandatory for clinical randomized control trials • But: Who else is using it (or not) and WHY?

  16. Arguments • Testing Distance measured for 6 meters • But: ETDRS can be done at 4, 2 and 1 m • Testing Time: 1 min for Snellen • But: ETDRS can be done condensed • Units • log MAR expressed as Snellen fraction Hussain et al., 2006

  17. Arguments • Consistency of measure • Need to run in parallel for some time • Cost: 1800.- CAN $ • Lesser measure comes at price of accuracy and precision in evidence-based medicine Hussain et al., 2006

  18. The “NEW” Discovery • DeCarlo DK, et al., IOVS 2006; 47: ARVO E-abstract 3474; Relationship Between ETDRS and Projected Snellen Visual Acuity in Patients With ARMD • Falkenstein I, et al., IOVS 2007; 48: ARVO E-abstract 2148; Comparison of Visual Acuity Measurements in Macular Degeneration Patients Tested With Snellen and LogMAR (ETDRS) Charts • Kaiser PK, IOVS 2008; 49: ARVO E-abstract 2249; Comparison of Snellen versus ETDRS Protocol Visual Acuities Performed by Certified Vision Examiners

  19. The “NEW” Discovery • Hussain, B., Saleh, G. M., Sivaprasad, S., & Hammond, C. J. (2006). Changing from Snellen to LogMAR: debate or delay? Clinical & Experimental Ophthalmology, 34(1), 6-8. • Beck et al. (2007). Visual acuity as an outcome measure in clinical trials of retinal diseases. Ophthalmology, 114(10), 1804-1809. • Falkenstein, et al. (2008). Comparison of visual acuity in macular degeneration patients measured with Snellen and Early Treatment Diabetic Retinopathy Study charts. Ophthalmology, 115(2), 319-323.

  20. Subspecialty: Low Vision • No news here: • Augustus Colenbrander • Measuring Vision and Vision Loss. In W. Tasman & E. A. Jaeger (Eds.), Duane's Ophthalmology (Vol. 5): Lippincott Williams & Wilkins. • Goal: Measure RESIDUAL Vision • Must be done with attention to detail

  21. Optometry & Acuity • This is their domain! • Bailey, I. L. (2006). Visual Acuity. In W. Benjamin & I. M. Borish (Eds.), Borish's Clinical Refraction (2nd ed.): Butterworth-Heinemann

  22. Meaningless Terms? • counting fingers, • hand-motion • light perception • Can be converted into useful scales • Schulze-Bonsel, et al. (2006). Visual acuities "hand motion" and "counting fingers" can be quantified with the Freiburg visual acuity test.Investigative Ophthalmology & Visual Science, 47(3), 1236-1240.

  23. Macular Degeneration Macular Hole Specialized Acuity Charts

  24. Specialized Letters • Rounded letters (S, O, C and D) are generally more difficult to distinguish • Can be language-dependent • Plainis, S., Tzatzala, P., Orphanos, Y., & Tsilimbaris, M. K. (2007). A modified ETDRS visual acuity chart for European-wide use.Optom Vis Sci, 84(7), 647-653.

  25. Optotypes

  26. Special Populations

  27. But: What does VA actually tell us? • Not much! • Resolution power at highest contrast at highest spatial frequency

  28. Spatial Contrast Sensitivity

  29. VA Limitations • Low/Middle Frequency loss is undetected • i.e. MS • VA rarely correlated with perceived visual function (patient perspective) when disease is involved • Contrast loss can be with/without VA loss

  30. VA and Face perception • Common complaint in patients • Face recognition involves multiple spatial frequencies • VA is only related when VA is “good”

  31. Face Acuity

  32. MARS Contrast Chart Colenbrander Low Contrast Chart ETDRS Chart

  33. How to test SCS clinically? But: Not presently commercially available anymore!

  34. Take-Home Message Evidence-based best practice = Apply the best tools

  35. Thank youQuestions?walter.wittich@mail.mcgill.ca

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