A Comprehensive Assessment of Anterior Corneal Power by Different Devices (No)

• Flat corneal power [ Time Frame: 2 weeks ] [ Designated as safety issue: No ]
  The intrasession repeatability and intersession reproducibility of flat corneal curvature measurements by using the 8 commercially available instruments.
• Steep corneal power [ Time Frame: 2 weeks ] [ Designated as safety issue: No ]
  The intrasession repeatability and intersession reproducibility of Steep corneal curvature measurements by using the 8 commercially available instruments.

• Flat corneal power [ Time Frame: 1 day, 2 weeks ] [ Designated as safety issue: No ]
  The intrasession repeatability (1 day) and intersession reproducibility (2 weeks) of flat corneal curvature measurements by using the 8 commercially available instruments.
• Steep corneal power [ Time Frame: 1 day, 2 weeks ] [ Designated as safety issue: No ]
  The intrasession repeatability (1 day) and intersession reproducibility (2 weeks) of Steep corneal curvature measurements by using the 8 commercially available instruments.

• Vector power J0 [ Time Frame: 2 weeks ] [ Designated as safety issue: No ]
  The intrasession repeatability and intersession reproducibility of vector power J0 measurements by using the 8 commercially available instruments.
• Vector power J45 [ Time Frame: 2 weeks ] [ Designated as safety issue: No ]
  The intrasession repeatability and intersession reproducibility of vector power J45 measurements by using the 8 commercially available instruments.

• Vector power J0 [ Time Frame: 1 day, 2 weeks ] [ Designated as safety issue: No ]
  The intrasession repeatability (1 day) and intersession reproducibility (2 weeks) of vector power J0 measurements by using the 8 commercially available instruments.
• Vector power J45 [ Time Frame: 1 day, 2 weeks ] [ Designated as safety issue: No ]
  The intrasession repeatability (1 day) and intersession reproducibility (2 weeks) of vector power J45 measurements by using the 8 commercially available instruments.

To comprehensively assess the precision and agreement of anterior corneal power measurements using 8 different devices.

Volunteers with healthy corneas will be measured by different instruments to detect their anterior corneal power. Only the right eye of each subject was selected. Measurements were repeated in the second session scheduled 1 to 2 weeks later.

The present study's definitions of reproducibility, repeatability and agreement were based on those adopted by the British Standards Institute and the International Organization for Standardization.

Corneal curvature measurement provides crucial information for calculating intraocular lens power,screening and managing corneal refractive surgeries and corneal disease.

Volunteers with healthy corneas will be measured by different instruments to detect their anterior corneal power.Only the right eye of each subject was selected.Measurements were repeated in the second session scheduled 1 to 2 weeks later, at almost the same time as the first session, by the same examiner using the same protocol.

Inclusion Criteria:

• healthy cornea,
• best corrected distance visual acuity (BCVA) equal to or better than 20/25,
• willing and able to comply with scheduled visits and other study procedures.

Exclusion Criteria:

• History of refractive surgery or any keratoplasty procedure,
• use of contact lenses,
• history of corneal dystrophies or degenerative diseases,
• history of glaucoma or ocular hypertension,
• significant subjective dry eye symptoms, Schirmer I test results of less than 5.0 mm, tear film break-up time shorter than 5 seconds and corneal fluorescein staining positive.