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W. M. Lau, D. C. Pye; The Effect of Overnight Corneal Edema and Diurnal Variation of Ocular Response Analyser and Goldmann Tonometry Measurements. Invest. Ophthalmol. Vis. Sci. 2010;51(13):566.
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© ARVO (1962-2015); The Authors (2016-present)
To investigate the possible influence of the diurnal variation of central corneal radius (CCR), central corneal thickness (CCT) and Ocular Response Analyse (ORA) measures of corneal hysteresis (CH) and corneal resistance factor (CRF) on diurnal Goldmann Applanation Tonometry (GAT) measurements.
25 healthy normals (age 21±2 years) had auto-keratometry, ORA, GAT and ultrasonic pachymetry readings taken every 2 hours between 17:00 to 23:00. Subjects then slept overnight for approximately 8 hours. No measurements were taken during this time. On the next day, readings were taken every 20 minutes from 07:00 to 09:00, and then at a 2 hour frequency until 17:00.
All variables showed a significant overnight increase (paired t-test, all p<0.05) with a trend for reduction during the corneal deswelling phase (between 07:00 to 09:00). All parameters except CCR and CH showed significant variation after 09:00 (repeated measures ANOVA, p<0.05). The relationship between changes in GAT and changes in CCT was significantly different during, and without, corneal deswelling (linear mixed models (LMM) 0.51±0.25 mmHg GAT change/10 µm CCT change, p<0.05). The association of changes in CRF with changes in GAT was similar during both time periods (LMM, 0.68 mmHg GAT change per mmHg CRF change, both p<0.05). Changes in CCR and CH were non-significant predictors of changes in GAT during both time periods.
The overnight increase in GAT was due to both changes in IOP and an overestimation error resulting from overnight corneal swelling. The similar behaviour of changes in CRF with respect to changes in GAT during and without corneal deswelling suggests CRF is IOP dependent and unaffected by small amounts of corneal edema. Diurnal changes in GAT were unrelated to changes in CCR and CH.
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