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Related Experiment Videos

Predicting visual performance following excimer photorefractive keratectomy.

W S Baron1, C Munnerlyn

  • 1Visx Inc, Sunnyvale, Calif.

Refractive & Corneal Surgery
|September 1, 1992
PubMed
Summary

Excimer photorefractive keratectomy can create duplex optical images, leading to visual side effects like halos. Low refractive errors are more prone to these visual disturbances than high refractive errors.

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Area of Science:

  • Ophthalmology
  • Optical Engineering
  • Visual Optics

Background:

  • Excimer photorefractive keratectomy (EPRK) can generate a duplex optical image when the ablation zone is smaller than the entrance pupil.
  • This phenomenon impacts visual performance and can lead to secondary visual effects.
  • A theoretical model is employed to analyze these optical image characteristics.

Purpose of the Study:

  • To analyze visual performance and secondary effects resulting from duplex optical images.
  • To investigate the relationship between optical parameters and visual outcomes after EPRK.
  • To understand the prevalence and predictors of visual side effects.

Main Methods:

  • A theoretical model was used to calculate the point-spread function (PSF).
  • The PSF incorporates an in-focus component and an annular out-of-focus component, derived from pupil size, ablation size, refractive error, and photoreceptor sensitivity.
  • Line-spread, edge-spread, and optical transfer functions were subsequently derived.

Main Results:

  • Secondary maxima and curvilinear ramps in spread functions were most prominent in cases of low refractive error.
  • The half-height widths of the point-spread and line-spread functions remained largely unchanged.
  • The optical transfer function reduction was proportional to the light distribution between the image components.

Conclusions:

  • Stable point and line spread function widths explain visual acuity's insensitivity to annular blur.
  • Contrast sensitivity correlates with perceived haze and fog.
  • Halos and ghost images are linked to secondary optical maxima and curvilinear ramps, particularly in low illumination and with low refractive corrections.
  • Visual acuity and contrast sensitivity do not predict halos or ghost images; high refractive errors yield fewer visual side effects.

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