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Retinal Image Height, Anisometropia and Aniseikonia

Retinal Image Height, Anisometropia and Aniseikonia. To calculate uncorrected retinal image height (  = 3 ) in a 5 D (F O ) axially myopic (reduced) eye, the parameter(s) that must be calculated specifically for that eye is/are:. M CR , reduced axial length, F S

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Retinal Image Height, Anisometropia and Aniseikonia

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  1. Retinal Image Height, Anisometropia and Aniseikonia

  2. To calculate uncorrected retinal image height ( = 3) in a 5 D (FO) axially myopic (reduced) eye, the parameter(s) that must be calculated specifically for that eye is/are: • MCR, reduced axial length, FS • MCR, reduced axial length • reduced axial length, FS • reduced axial length

  3. To avoid retinal aniseikonia in an axially anisometropic patient, the most appropriate correction would be: • contact lenses • a contact lens for one eye and spectacle lens for the other • spectacles at the shortest practical vertex distance • spectacles at a relatively long vertex distance

  4. For a patient with axial myopia, the effect of a spectacle correction at Knapp’s Plane is to: • decrease the size of the retinal image so that it equals that of the standard emmetropic eye • produce no change between uncorrected and corrected retinal image height • increase the size of the retinal image so that it equals that of the standard emmetropic eye • produce the effect as that of a contact lens correction on retinal image height

  5. Page 11.15 Refractive Ametropia

  6. Refractive Ametropia (a) Uncorrected

  7. P FE FH FM CHIEF RAY   hE CHIEF RAY RI Height in Uncorrected Refractive Ametropia Page 11.15 hE = hU (M) = hU (H)

  8. RI Height & Correction of Refractive Ametropia • Uncorrected RI heights the same in all refractive ametropes • Any difference in retinal image height after correction will therefore be due to differences in spectacle magnification (O.D. vs. O.S.) • To avoid aniseikonia in refractive anisometropia  want both correcting lenses to have same SM •  want to prescribe contact lenses to avoid aniseikonia in refractive anisometropia

  9. Pp. 11.16-17 Example 11.2

  10. Pp. 11.16-17

  11. Fig 11.9 Looking at same object (same  and ) Left Eye: hU ?? Same ax as right  hU (Left) same as hU (Right) = 0.728 mm

  12. hE hM

  13. Compare corrected RI heights hH hH hM hM

  14. Page 11.18 Summary: Corrected Retinal Image Height in Axial and Refractive Anisometropia

  15. Knapp’sPlane ReducedSurface HIGH My LOW Hy Em My LOW Fe HIGH Hy hem hS (A) d AXIAL AMETROPIA Eliminate ANK with spectacles at Knapp’s Plane Variation in Corrected RI Height: Axial Ametropia This figure is a graph NOT an optical diagram Page 11.18

  16. ReducedSurface Hy HIGH LOW Em Eliminate ANK with contact lenses LOW HIGH My hem hS (R) d BASELINE REFRACTIVE AMETROPIA Variation in Corrected RI Height: Refractive Ametropia This figure is a graph NOT an optical diagram Effectively an SM plot for each magnitude of ametropia

  17. Zero ANK here Zero ANK here Variation in Corrected RI Height with Ametropia Knapp’sPlane ReducedSurface ReducedSurface Hy HIGH HIGH My LOW LOW Hy Em My LOW LOW Fe HIGH HIGH Hy My hem hS (A) hS (R) d d BASELINE AXIAL AMETROPIA REFRACTIVE AMETROPIA

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