Page 97 - A Magyar Szemorvostársaság 2023. évi kongresszusa - Tudományos program és előadáskivonatok

the index of surface variation (ISV). For descriptive purposes, observed limits (minimum,
maximum) of outcome variables were used to derive observed ranges of within-subject diurnal
change. To assess diurnal variation by regression modelling, estimates of differences between
daily extremes were adjusted for age and subject group (nurses, who do night-shift work,
versus not nurses), in multilevel mixed-effects linear regression. P values <0.05 were
interpreted as indicating a significant difference.

Results: Altogether 1636 measurements were made. Significant diurnal changes were
observed in case of K1 F, K2 F/B, Astig F/B, Asph F/B, Pachy Min, Vol D 10 and ISV (p <
0.0001), and also for K1 B (p = 0.0002), but no significant variation could be detected in case
of Axis F/B. The cornea after 12.00 is the thinnest during the day and early in the morning,
before 6.00 a.m. is the thickest. The variations of the anterior surface keratometric parameters
are very similar (before 11.00 a.m. is the highest and before 6.00 a.m. is the lowest) while the
fluctuations of the posterior surface parameters (keratometry, astigmatism, asphericity) are not
parallel.

Conclusions: The cornea shows significant diurnal variations. The fluctuations of the anterior
surface are more profound than of the posterior surface, which can be the consequence of
more substantial variations of the surrounding environment than the aqueous humour
contacting to the posterior surface of the cornea. Further studies are required to reveal the
effects of diurnal variations on the quality of vision and to provide valid information for the
planning of the different interventions of refractive surgeries.