subjective refraction
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subjective refraction

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subjective refraction Presentation Transcript

  • 1. Refraction
  • 2. What is Refraction? Determination of the refractive status (prescription) of the eye. OBJECTIVE SUBJECTIVE Retinoscopy Subjective Refraction
  • 3. Subjective Refraction To determine by subjective means the combination of spherical and cylindrical lenses necessary to to provide best visual acuity. (with accommodation relaxed)
  • 4. Principles of Refraction1. Accommodation-relaxed state2. Maximum PLUS, minimum minus3. Always trial frame before prescribing4. Take into account vertex distance especially for high prescription individuals
  • 5. How to ensure accommodation is relaxed? Use PLUS lens to FOG Ensure image is located infront of retina This causes image / VA to become worse if eye attempts to accommodate (Image point becomes further away from the fovea)
  • 6. STEPS IN SUBJECTIVE REFRACTIONStart from Auto-Ref Results (OD) Repeat 1-3 M O V 1. Best Vision Sphere E OU T 2. Jackson Cross Cylinder O 4. Binocular Balancing O S 3. Best Vision Sphere 5. Binocular Best Sphere
  • 7. STEPS IN SUBJECTIVE REFRACTIONStart from Auto-Ref Results (OD)Start from Ret Results (OD) Repeat 1-3 M O V 1. Best Vision Sphere E OU T 2. Jackson Cross Cylinder O 4. Binocular Balancing O S 3. Best Vision Sphere 5. Binocular Best Sphere
  • 8. How to achieve BVS? Strongest positive spherical lens to give best VA FOGGING DUOCHROME
  • 9. FOGGING TO ACHIEVE BVS Place enough PLUS lenses to FOG vision to ~6/12 line ROT: every line= ~0.25 DS Slowly reduce the plus power until best VA is obtained Remember:“Maximum plus power for best visual acuity”
  • 10. USING DUOCHROME TEST TOACHIEVE BVS PT TPBased on chromatic aberrationPatient asked: “ Are LETTERS in the red darker orLETTERS in the green darker?”Green letters clearer = Add ‘+ 0.25DS’Red letters clearer = Add ‘- 0.25DS’End-point is obtained when the letters on the Red-Green chart appears equally dark or when a reversaloccurs.
  • 11. STEPS IN SUBJECTIVE REFRACTIONStart from Auto-Ref Results (OD)Start from Ret Results (OD) Repeat 1-3 M O V 1. Best Vision Sphere E OU T 2. Jackson Cross Cylinder O 4. Binocular Balancing O S 3. Best Vision Sphere 5. Binocular Best Sphere
  • 12. STEP 2: JACKSON CROSS CYLINDER(JCC) JCC used to find used to determine the cylindrical axis and the cylindrical power for the patient.
  • 13. Determining Cylinder Axis Patient directed to observe a round target Align dots with trial lens axis ie: 180 OR
  • 14. Determining Cylinder Axis JCC is flipped such that two views are shown Patient asked: “Is view one rounder, sharper, clearer or view two?” FLIP VIEW 1 VIEW 2
  • 15. Refining the axis If view one is clearer turn trial lens’ axis Turn 10 degrees TOWARDS red lines (~5-10 degrees) VIEW 1
  • 16. Patient directed to observe a round targetRefining the axis Align dots with trial lens axis ie: 170 JCC is flipped again such that two views are shown Patient asked: “Is view one rounder, sharper, clearer or view two?” FLIP VIEW 1 VIEW 2
  • 17. Refining the axis If view two is clearer turn trial lens’ axis TOWARDS red lines (~5 degrees) VIEW 2 Turn 5 degrees
  • 18. Determining Cylinder Power Patient directed to observe a round target Align red lines OR white lines to trial lens axis OR
  • 19. Determining Cylinder Power JCC is flipped such that two views are shown Patient asked: “Is view one rounder, sharper, clearer or view two?” FLIP VIEW 1 VIEW 2
  • 20. Determining Cylinder Power If view one is clearer, ADD -0.25 DC To maintain the circle of least confusion on the retina, a +0.25DS is added for every -0.50DC
  • 21. Determining Cylinder Power If view one is clearer, ADD +0.25 DC To maintain the circle of least confusion on the retina, a -0.25DS is added for every +0.50DC
  • 22. STEPS IN SUBJECTIVE REFRACTIONStart from Auto-Ref Results (OD)Start from Ret Results (OD) Repeat 1-3 M O V 1. Best Vision Sphere E OU T 2. Jackson Cross Cylinder O 4. Binocular Balancing O S 3. Best Vision Sphere 5. Binocular Best Sphere
  • 23. How to achieve BVS? Strongest positive spherical lens to give best VA FOGGING DUOCHROME
  • 24. STEPS IN SUBJECTIVE REFRACTIONStart from Auto-Ref Results (OD)Start from Ret Results (OD) Repeat 1-3 M O V 1. Best Vision Sphere E OU T 2. Jackson Cross Cylinder O 4. Binocular Balancing O S 3. Best Vision Sphere 5. Binocular Best Sphere
  • 25. STEPS IN SUBJECTIVE REFRACTIONStart from Auto-Ref Results (OD)Start from Ret Results (OD) Repeat 1-3 M O V 1. Best Vision Sphere E OU T 2. Jackson Cross Cylinder O 4. Binocular Balancing O S 3. Best Vision Sphere 5. Binocular Best Sphere
  • 26. STEP 4 BINOCULAR BALANCING The technique is also known as "equalising". During the monocular refraction, a different state of relaxation of accommodation may occur because one eye was under test while the other was not. Thus, binocular balancing is performed to balance accommodation between eyes. ALTERNATE HUMPHRISS OCCLUSION IMMEDIATE CONTRAST
  • 27. BB: Alternate Occlusion Used only when VA is EQUAL in both eyes1. Fog both eyes with + 0.75DS2. Direct patient to view 3 lines above best VA3. Alternately occlude each eye for ~0.5 secs each while asking patient: “ Which eye sees clearer/sharper?”4. Add +0.25DS to the better eye5. Repeat step 3 and 4 until both eye’s vision is equalised6. Slowly reduce fog until best VA is reached
  • 28. BB: Humphriss immediate contrast Used when VA is EQUAL or UNEQUAL between both eyes1. Fog OS with +0.75DS2. Direct patient to view OD’s best VA line3. (Perform BVS in OD)4. Add +0.25DS in OD VA same or better Add +0.25DS, VA worse remove +0.25, until you achieve max plus min minus5. Repeat Step 1-3 to test OS
  • 29. STEPS IN SUBJECTIVE REFRACTIONStart from Auto-Ref Results (OD)Start from Ret Results (OD) Repeat 1-3 M O V 1. Best Vision Sphere E OU T 2. Jackson Cross Cylinder O 4. Binocular Balancing O S 3. Best Vision Sphere 5. Binocular Best Sphere
  • 30. BINOCULAR BEST VISION SPHERE After binocular balancing, spherical lenses are added in front of the 2 eyes at the same time to determine the Binocular Best Sphere. The most plus/ least minus lens that would not reduce VA would be the end-point. Strongest positive spherical lens to give best VA1. Direct patient to view best OU VA2. ADD +0.25DS VA same= Add +0.25DS (Repeat with additional +0.25DS), VA worse= Remove +0.25DS
  • 31. STEPS IN SUBJECTIVE REFRACTIONStart from Auto-Ref Results (OD)Start from Ret Results (OD) Repeat 1-3 M O V 1. Best Vision Sphere E OU T 2. Jackson Cross Cylinder O 4. Binocular Balancing O S 3. Best Vision Sphere 5. Binocular Best Sphere
  • 32. What about for reading?“I can see clearly at distance, but I can’t read my newspapers!”
  • 33. Near Addition Presbyopic patients would require a near addition for their reading.
  • 34. Finding the Near Addition Step 1: Estimation from patient’s age Age (in Years) Estimated Add (in D) 40 - 45 + 0.50 to + 1.00 46 - 50 + 1.25 to + 1.75 51 - 55 + 2.00 to + 2.50 56 - 60 + 2.50 to + 2.75 61 - 65 + 2.50 to + 2.75 66 - 70 + 2.50 to + 2.75 70 + + 2.50 and Above
  • 35. Finding the Near Addition Step 2: Place the estimated near addition on top of the distance prescription Step 3: Patients holds the near vision chart at habitual distance. The amount of near add is then adjusted to position the patient’s habitual reading distance in the middle of the range of clear vision.
  • 36. Range of clear vision 40CM Patient’s habitual reading distance in the middle of the range of clear vision. 20CM 60CM
  • 37. Range of clear vision 40CM If range is too close to patient: Add -0.25DS in steps 10CM 50CM
  • 38. Range of clear vision 40CM If range is too far to patient: Add +0.25DS in steps 30CM 70CM
  • 39. Instruments for Refraction Trial lens set and frame Phoropter
  • 40. Two sets of commonly usedinstruments
  • 41. Clinical notes for trial lens and trialframe Spherical lenses are usually placed first in the trial frame, while cylindrical lenses are then placed in the front of the spherical lenses. When there are 2 or more spherical lenses, the one with the strongest power should be placed in the cell closest to the eye.
  • 42. Adjusting Sphere Powers
  • 43. Adjusting Cylinder Powers and Axis
  • 44. Cross Cylinder