The relationship between diurnal variations in intraocular pressure measurements and central corneal thickness and corneal hysteresis
Aachal Kotecha 1*,
David P. Crabb 2,
Alexander Spratt 3,
and
David F. Garway-Heath 4
1 NIHR Biomedical Research Centre for Ophthalmology, Moorfields Eye Hospital and UCL Institute of Ophthalmology, London, United Kingdom; Optometry and Visual Science, City University, London, United Kingdom
2 Optometry and Visual Science, City University, London, United Kingdom
3 Glaucoma Research Unit, Moorfields Eye Hospital, London, United Kingdom
4 NIHR Biomedical Research Centre for Ophthalmology, Moorfields Eye Hospital and UCL Institute of Ophthalmology, London, United Kingdom; Glaucoma Research Unit, Moorfields Eye Hospital, London, United Kingdom; Optometry and Visual Science, City University, London, United Kingdom
* To whom correspondence should be addressed. E-mail: aachalkotecha{at}gmail.com.
 |
Abstract |
|---|
Aims: To examine the relationship between office-hour changes in IOP, measured with the Goldmann applanation tonometer (GAT) & dynamic contour tonometer (DCT), and central corneal thickness (CCT) and corneal hysteresis (CH).
Methods: 62 eyes of 62 untreated glaucoma or normal subjects had IOP measured with the GAT and DCT over an 8 hour period at 2-hourly intervals. CCT (µm) was measured using a non-contact optical low-coherence reflectometry pachymeter and CH (mmHg) was measured with the Reichert Ocular Response Analyzer.
Results: GAT, DCT and CCT changed significantly (ANOVA; GAT: F = 19.9, p<0.001; DCT: F = 4.6, p=0.001; CCT: F = 16.4; p<0.001). No significant changes were observed in CH. Multilevel modelling of the inter-relationships between CCT, CH and age on IOP revealed that CCT and CH changes were significantly associated with GAT IOP changes ( GAT IOP/ CCT slope: 0.04 mmHg/µm, 95% CI 0.02 to 0.06; GAT IOP/ CH slope 0.20 mmHg/mmHg, 95% CI 0.01 to 0.39) . CCT changes were significantly associated with DCT IOP changes (DCT IOP/CCT slope: 0.03 mmHg/µm, 95% CI 0.00 to 0.05). The association between CCT and GAT IOP was relatively uniform between subjects; association between CCT and DCT IOP showed greater inter-subject variability. Age had no effect.
Conclusions: Measured IOP and corneal characteristics co-vary during office hours. Changes in CCT and CH are associated with changes in GAT and, less consistently, with DCT. The data suggests that variations in corneal characteristics may explain a small proportion of the change in IOP measurements made with the GAT during office hours.
Key Words:
corneal biomechanics, intraocular pressure, tonometry
