Reproducibility of keratometric measurements decreases with time after blinking

Area of Science:

• Ophthalmology
• Optometry
• Corneal Physiology

Background:

• Accurate keratometry is crucial for refractive surgery and contact lens fitting.
• Tear film stability is essential for consistent ocular surface measurements.
• Previous studies have not fully quantified the impact of blinking intervals on keratometry reproducibility.

Purpose of the Study:

• To investigate the reproducibility of keratometry measurements over time after a blink.
• To assess the influence of tear film break-up on simulated keratometric values (K1, K2), surface regularity index (SRI), and surface asymmetry index (SAI).

Main Methods:

• Thirty healthy subjects underwent corneal topography measurements at 5, 15, 30, and 60 seconds post-blink.
• Measurements were repeated three times per individual using a standard corneal topographic instrument.
• Analyzed were mean values, standard deviation, and reproducibility error for K1, K2, SRI, and SAI.

Main Results:

• While mean K1 and K2 values remained stable, measurement error significantly increased over time (p=0.007 for K1, p=0.038 for K2).
• Mean SRI values changed significantly (p=0.034) with time, but measurement error did not increase.
• SAI showed a non-significant trend of elevation over the 60-second period (p=0.093).

Conclusions:

• Tear film break-up significantly degrades keratometry measurement reliability during prolonged, non-blinking gaze.
• The induced error can surpass 0.6 D, considered clinically unacceptable.
• Clinicians should avoid prolonged gaze without blinking during eye examinations to ensure accurate keratometric data.