Effect of spherical aberrations on aberrometer-predicted refraction and manifest refraction

1
The authors have nothing to declare regarding
conflicts of interest or commercial relationships.
Effect of spherical aberrations on
aberrometer-predicted refraction and manifest
refraction
Jinho Jeong1, Mee Kum Kim2, Won Ryang Wee2
Department of Ophthalmology Jeju National
University Hospital, Jeju, Korea1 Seoul National
University Hospital, Seoul, Korea2
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Backgrounds

• Stiles-Crawford Effect
• 1937, W.S. Stiles B.H. Crawford
• The directional sensitivity of the cone
• light passing near the edge of the pupil (a
  marginal ray) is less efficient at evoking
  sensation than light passing through the center
  of the pupil
• Works on photopic condition

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Backgrounds

• The SCE has been reported not to act on rods and
  its directional selectivity is considered to be
  least effective in the scotopic condition.
• Human neurons recognize central rays more
  selectively according to the SCE, but on the
  other hand, aberrometers do not have directional
  selectivity. Therefore, differences between
  manifest refraction and aberrometer predicted
  refraction could occur if measurements were taken
  in the photopic condition. However, these
  measurements are usually conducted in the
  scotopic condition, and the SCE needs evaluation
  under these environments.
• In this study, we compared refractive errors
  measured by manifest refraction with those
  predicted by an aberrometer, both measurement
  types were conducted in the scotopic condition,
  and the role of the SCE was evaluated by
  analyzing correlations between spherical
  aberrations and discrepancies between refraction
  results.

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Purpose

• Purpose To evaluate the influence of the
  Stiles-Crawford effect (SCE) on manifest
  refraction and aberrometer predicted refraction
  in pseudophakic eyes.
• Design Retrospective review of diagnostic tests
• Participants 73 eyes of 45 patients that
  underwent uneventful cataract surgery.

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Methods

• The records of 73 cases with uneventful cataract
  surgery were retrospectively reviewed.
• 1 month after surgery, manifest refraction (MR)
  was assessed, and ocular aberrations, aberrometer
  predicted refraction (APR), and mesopic pupil
  size were measured using a Wavescan 1 (VISX,
  Santa Clara, CA).
• APR was calculated for a 4 mm pupil. Refraction
  gap was calculated by subtraction APR spherical
  equivalents (SEs) from MR SEs, and correlations
  of refraction gap between high order aberration,
  pupil size, and refractive error were analyzed.

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Results
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Results
Paired samples t-test Manifest refraction -
Aberrometer predicted refraction
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Results
The mean refraction gap was -0.28 0.26 D (range
-0.76 to 0.44 D), and MR SEs were significantly
more myopic than APR SEs (paired t test
plt0.001). APR and MR were found to be
significantly correlated with each other
(R0.963), and the distribution of the refractive
gap qualified 95 limit of agreement, which
ranged from -0.84 D to 0.24 D.
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Results
Correlations between refraction gap and
refractive error, pupil size, and high order RMS.
Refraction gap was measured by subtracting
aberrometer predicted refraction from manifest
refraction.
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Results
According to multiple regression analysis,
spherical aberrations were significantly
correlated with refraction gaps (R0.508). As
spherical aberration increased, APR became more
myopic than MR. Refractive error and pupil size
were not found to be significantly related to
refraction gap
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Discussions
Schematic presentation of spherical aberration
effects at a focal point. Spherical aberrations
are caused by peripheral rays, and the minimum
circle of confusion moves in a more myopic
direction in eyes with a positive spherical
aberration and in a more hyperopic direction in
eyes with a negative spherical aberration. When
the Stiles-Crawford effect is taken into account,
central rays are more weighted and the focal
point remains unchanged despite the presence of
spherical aberrations.
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Discussions

• We regard that MR with the SCE may represent the
  refractive state of day vision and APR without
  SCE represents for night vision, although some
  modulation may be necessary to make direct
  comparisons.
• We expect that both MR and APR results should be
  taken into consideration when assessing a
  patients refractive status, and these results
  would also be useful for deciding on ablation
  amounts during corneal refractive surgery in the
  presence of a refraction gap between MR and APR.
• Based on our results, we would expect a 0.4 D
  refraction gap for a 0.2 µm spherical aberration
  change.

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Conclusion

• The Stiles-Crawford effect was found to influence
  manifest refraction results.
• In terms of the interpretation of aberrometer
  predicted refraction, SCE and spherical
  aberrations should be weighted when the
  relationships with MR are being investigated
• Both MR and APR results should be taken into
  consideration when assessing a patients
  refractive status