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Related Experiment Videos

Location of the major corneal reference points

R B Mandell1, C S Chiang, S A Klein

  • 1School of Optometry, University of California, Berkeley, USA.

Optometry and Vision Science : Official Publication of the American Academy of Optometry
|November 1, 1995
PubMed
Summary

Corneal topography measurements show minimal differences when aligned with the corneal sighting center. However, aligning with the corneal apex reveals significant variations in power, toricity, and axis, particularly in the periphery.

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Area of Science:

  • Ophthalmology
  • Optometry
  • Biomedical Engineering

Background:

  • Corneal topography is crucial for contact lens design and refractive surgery prediction.
  • Key applications rely on measurements referenced to the corneal apex (shape) and corneal sighting center (power).

Purpose of the Study:

  • To compare videokeratography measurements using standard alignment versus alignment at the corneal sighting center and corneal apex.
  • To evaluate the impact of reference point alignment on corneal power, toricity, and axis measurements.

Main Methods:

  • Videokeratography was used to measure instantaneous corneal power, toricity, and axis in 20 eyes.
  • Measurements were taken using standard instrument alignment, corneal sighting center alignment, and corneal apex alignment.

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Main Results:

  • Aligning with the corneal sighting center showed minimal differences (<0.50 D) in central corneal power, toricity, and axis compared to standard alignment.
  • Aligning with the corneal apex resulted in significant differences (>0.50 D for power, >10 degrees for axis) compared to standard alignment, especially in the corneal periphery.

Conclusions:

  • Standard videokeratography alignment is comparable to corneal sighting center alignment for central corneal measurements.
  • Corneal apex alignment introduces significant variability, particularly for peripheral measurements, impacting accuracy in refractive surgery planning and lens design.