The Association Between Diurnal Variation of Optic Nerve Head Topography and Intraocular Pressure and Ocular Perfusion Pressure in Untreated Primary Open-angle Glaucoma

Purpose: To investigate the hypotheses that the topography of the optic nerve head (ONH) significantly changes during the day in untreated primary open-angle glaucoma (uPOAG) and healthy volunteers; and that there is a significant association with diurnal variations of intraocular pressure (IOP) and mean ocular perfusion pressure (MOPP). Methods: Fourteen uPOAG and 14 age-matched normals were included. IOP, blood pressure, and ONH topography were measured between 7: 00 AM and 10: 00 PM. MOPP was calculated. A mixed-effect repeated measures analysis was done. Variance component analysis was done for glaucoma and normal groups separately based on the mixed-effect models. Results: The cup volume, rim volume, and cup shape measure in the temporal (T) and temporal-inferior (TI) sectors were significantly different between the 2 groups (P< 0.05). The highest variance component was owing to "patients" whereas "time" had the smallest contributed percentage. Cup volume (T and TI) and reference height (RH) showed a significant (P< 0.001) diurnal change in uPOAG. Rim volume (T and TI) showed a significant diurnal change in normals (P <= 0.01). There was no significant (P> 0.05) association between the change in IOP, MOPP, and ONH topography in either group. There was a significant association between cup volume and RH in both groups (P< 0.001, global and T). There was a significant association between MOPP and RH in both groups (P< 0.001). Conclusion: The ONH topography significantly changed during the day in both groups. The change in ONH topography was associated with the change in reference height, which in turn was associated with MOPP. These findings suggest that the time of the day and the level of perfusion pressure should be considered when evaluating ONH topography using the HRT. Repeated measures are recommended when evaluating ONH topography.