Successfully reported this slideshow.
We use your LinkedIn profile and activity data to personalize ads and to show you more relevant ads. You can change your ad preferences anytime.

Subjective refraction

4,418 views

Published on

Subjective refraction

Published in: Healthcare
  • I tried Semenax and noticed results after 3 days! I had tried other products... But Semenax WORKS! ♥♥♥ https://bit.ly/2No6XLF
       Reply 
    Are you sure you want to  Yes  No
    Your message goes here

Subjective refraction

  1. 1. SUBJECTIVE REFRACTION OPTOM FASLU MUHAMMED
  2. 2. REFRACTION PROCEDURE: DISTANCE 2 1. Visual acuity (VA) with current Rx VA versus spherical Rx table • Spectacles • AR • Retinoscope • Unaided 2. Perform Pinhole test Unaided VA with existing Rx if aided VA is worse than 6/12
  3. 3. REFRACTION PROCEDURE: DISTANCE 3. Determine Best Vision sphere 3 • Letter Chart • Duochrome 4. Estimate Astigmatism • VA with BVS • Refractive Error Estimation table
  4. 4. 4 5. Refine Astigmatism (cylinder) • Axis location • Astigmatic power - Fan & Block - Jackson X-cyl - Cyl trial lens Rotation & Letter chart 6. Refine Sphere of Rx • +1.00 DS Fog to blur vision Refraction Procedure: Distance
  5. 5. REFRACTION PROCEDURE: DISTANCE 5 7. Bi-Ocular balance • Simultaneous • Alternating - Prism Dissociation - Polaroid 8. Final Rx• Option s
  6. 6. REFRACTION PROCEDURE: NEAR ADD 1. Establish Preferred Near Viewing Distance 6 2. Determine Near Blur Point • Binocular • Monocular recheck – near letter chart – measuring tape • Binocular – measuring tape
  7. 7. REFRACTION PROCEDURE: NEAR ADD 3. Calculate Near ADD required 7 • Maintain half (50%) the Amplitude of Accommodation in reserve - nomogram, nomograph (in the workbook) 4. Refine ADD • Range of clear vision - near letter chart - trial lens
  8. 8. LOGMAR CHARTS •The design principles suggested by Bailey & Lovie •More lines than a typical Snellen chart, particularly at poor VA levels •Not truncated to 6/5 (20/15) or similar.
  9. 9. TYPES  ADULTS – Bailey–Lovie Charts – ETDRS charts  CHILDREN – The Glasgow Acuity Cards  Keeler crowded logMAR charts
  10. 10. PROCEDURE  The luminance of the chart should be between 80 and 320cd/m2.  Seat the patient comfortably with an unobstructed view of the test chart.  You should sit in front and to one side of the patient in order to monitor facial expressions and reactions.
  11. 11. •They should be pushed to determine whether they can see any more. •If they make four or more mistakes on a line of five •Ask them to move closer if chart not seen
  12. 12. If the patient cannot see the letters even at the closest test distance a) Hand Movements (HM) @ Y cm b) Light Projection (Lproj.):50 cm c) Light Perception (LP): Repeat measurements for the other eye and binocularly.
  13. 13. Since each letter is worth an equal 0.02 log units, you can most accurately determine visual acuity by accounting for every letter correctly identified. Typically, an equation is used to calculate VA: logMAR VA = 1.1 - (0.02 x letters missed)
  14. 14. MOST COMMON ERRORS 1. Allowing cautious patients to decide their acuity (i.e. not pushing them to guess). 2. Permitting the patient to screw their eyes up and improve their VA. 3. Permitting the patient to look around the occluder or through their fingers and view binocularly when measuring monocular VA. 4. Taking distance VAs in a PAL or varifocal wearer when they are not looking through the distance vision section of the lens. 5. Using an incorrect working distance. 6. Not recording the result immediately and guessing the result at the end of the examination.
  15. 15. VA MEASUREMENT USING SNELLEN CHART  Procedure is similar to logMAR chart  Vn is recorded as the smallest line in which the majority of letters are seen,irrespective of subjective blurr.  Errors are recorded by appending a -1,-2, or -3 to snellen fraction Eg:6/9(-2),6/9(-3)… If pt couldn’t see 6/60 letter @ 6m,but could @ 2m,recorded as 2/60.
  16. 16. RECORDING  The Snellen fraction is defined as:  Test Distance /Distance at which the letters subtend 5 min of arc. 1. Test distance can be provided in metres (metric) or feet (imperial). 1. Snellen VA can be labelled in either decimal or conventional Snellen notation
  17. 17. Snellen Fraction = Test Distance Distance at which entire letter subtends 5’ The acuity test distance should be long enough to not stimulate the accommodative system. By convention, the standard test distance in the U.S. has been 20 feet. Everywhere else it is 6 meters: 20 is a Snellen fraction in feet 60 6 is the same Snellen fraction 18 in metric units Measuring visual acuity: The Snellen Fraction
  18. 18. Measuring Distance Visual Acuity Testing Sequence By convention you always test in the following order 1st OD ocular dexter Right eye (cover left eye) 2nd OS ocular sinister Left eye (cover right eye) 3rd OU ocular utrique Both eyes
  19. 19. Measuring Distance Visual Acuity: Example 2 A P E O T F 20/25 E V O C T Z 20/20 O H P N T C 20/15 What is the visual acuity of this patient? 5/6 letters on the 20/25 line and only 2 letters on the 20/20 line No reason to even test the 20/15 line The visual acuity can be expressed as 20/25 However, accounting for the missed and identified letters... The VA can be more descriptively expressed as 20/25-1/+2
  20. 20. MONOCULAR SUBJECTIVE RX Letter Chart Duochrome test Combination 22 Spherical Correction = Best vision sphere (BVS) Obtain spherical correction giving best VA
  21. 21. MONOCULAR SUBJECTIVE RX Starting point for BVS  Sphere component of Spec Rx  Sphere component of Auto-Rx  Unaided VA Estimation Method 23 BVS = (Sphere Rx) + (Astigmatic Rx ÷ 2) Best Vision Sphere (BVS)
  22. 22. VISUAL ACUITY Snellen 6/VA Decimal MAR (Minutes of Arc) logMAR 3 2.00 0.50 -0.30 4 1.50 0.67 -0.18 5 1.20 0.83 -0.08 6 1.00 1.00 0.00 7.5 0.80 1.25 0.10 9 0.67 1.50 0.18 9.5 0.63 1.58 0.20 12 0.50 2.00 0.30 15 0.40 2.50 0.40 18 0.33 3.00 0.48 19 0.32 3.17 0.50 24 0.25 4.00 0.60 30 0.20 5.00 0.70 36 0.17 6.00 0.78 38 0.16 6.33 0.80 48 0.13 8.00 0.90 60 0.10 10.00 1.00 120 0.05 20.00 1.30 24
  23. 23. RELATIONSHIP BETWEEN REFRACTIVE ERROR AND VA 25 Vision 6/6 (20/20) 6/9 (20/30) 6/12 (20/40) 6/18 (20/60) 6/24 (20/80) 6/36 (20/120) 6/60 (20/200) Spherical* small 0.50 0.75 1.00 1.50 2.00 2.00 to 3.00 Astigmatic small 1.00 1.50 2.00 3.00 4.00 high Refractive Error (D) Bennett and Rabbetts, 1984 * Myopia or absolute hypermetropia
  24. 24. RELATIONSHIP BETWEEN REFRACTIVE ERROR AND VA 26 Vision 6/6 (1.00) 6/9 (0.67) 6/12 (0.50) 6/18 (0.33) 6/24 (0.25) 6/36 (0.13) 6/60 (0.10) Spherical * < 0.50 0.50 0.75 1.00 1.50 2.00 2.00 to 3.00 Astigmatic < 0.75 1.00 1.50 2.00 3.00 4.00 > 4.00 Refractive Error (D) Bennett and Rabbetts, 1984 * Myopia or absolute hypermetropia
  25. 25. ESTIMATE RESIDUAL SPHERICAL ERROR: DISTANCE RX 27 • Note the Best Snellen VA obtained • Estimate the Amount of Spherical Error Procedure Residual Spherical Error = Snellen (metric) VA Denominator ÷16
  26. 26. ESTIMATE RESIDUAL SPHERICAL ERROR: DISTANCE RX Unaided Visual Acuity RE LE Patient A Spherical Rx Snellen 6/12 Snellen 6/9 Patient B Spherical Rx Snellen 20/30 Snellen 20/60 Patient C Spherical Rx Decimal VA 0.1 Decimal VA 0.17 Patient D Spherical Rx MAR 4 logMAR 0.7 28 0.75D 0.56D 0.56D 1.12D 2.25D3.75D 1.50D 1.75D
  27. 27. MONOCULAR SUBJECTIVE RX • Use the ‘highest plus’ sphere as a starting point • Add plus lenses in 0.50 steps until VA begins to decrease • Then add negative lenses in 0.25D steps until there is no further VA improvement: “Does this lens make the letters clearer or just smaller and darker?” 29 Refinement: Sphere (BVS) Letter Chart
  28. 28. SPHERICAL CORRECTION Points to note:  Accommodation  if the letters get darker and smaller only, then too much minus has been prescribed  When adding plus lenses, assure the patient you know it is getting worse 30 Letter Chart
  29. 29. SPHERICAL CORRECTION Duochrome (starting point) 31 Combination Tests Letter chart (refinement) Duochrome (end point) Letter chart (BVS) OR

×