PURPOSE: To assess accuracy and reproducibility of retinal vessels caliber measurement in Heidelberg retina tomographer (HRT II) images by new developed method.
METHODS: 76 images of optic nerve head were obtained from 76 eyes. Eight vessels' diameters were measured in each case in the area of 0.5 to 1.0 disc diameter from the optic disc margin. The window for "interactive measurements" was used to determine three-dimensional coordinates (x,y,z) of each vessel diameter. Diameter of each vessel was calculated according to the Pythagorean Theorem (value of "z" coordinate remained unchanged).
RESULTS: Diameter of retinal arterioles varied from 55,0 to 106,5 μm. Diameter of retinal venulas ranged from 68,9 to 140,1 μm. The standard deviation value changed from 0,6 to 16 micron. Artetiole/venule ratio mean value was 0,702±0,039.
CONCLUSIONS: Measurement of retinal vessels diameter in images obtained during retinal tomography is exact and informative. The described method is the unique way of retinal vessels caliber measurement in absolute values.
The assessment of optic nerve head (ONH) stability in measured short-term increase of intraocular pressure (IOP) in healthy group and initial primary open angle glaucoma (POAG) patients. METHODS: 147 healthy people were divided in two groups according to the age. The first one (59 people) was comprised of those who were from 16 to 35 years old. The second group included 88 healthy adults from 35 to 78. 64 patients (39 - 80 years old) with initial POAG were included in the third group. The mean cup depth (MCD) of the optic disc was determined with the Heidelberg retina tomographer (HRT II). After baseline examination a suction cup was used to increase IOP for 10 mm Hg above baseline and MCD was determined again. IOP level was controlled by Perkins’ tonometer before and during suction. RESULTS: IOP increase always resulted in MCD increase. In group 1 mean increase was 18,3±1,96 μm. In the second group the value was 22,4±2,63 μm. There was no statistically significant difference in MCD mean increase values in groups 1 and 2 (t=1,46, p>0,05). In POAG group mean MCD increase was 49,2±8,41 μm. The difference of this value was statistically significant when compared with that in group 2 (t=5,38, p<0,05). CONCLUSIONS: 1. There was no correlation between age and MCD mean increase in healthy people. 2. Results of the investigation permit us to establish criteria of normal and decreased stability of ONH to the induced elevation of IOP: we consider the MCD increase less than 25 μm as normal, 25 - 40 μm as borderline and more than 40 μm as lack of lamina cribrosa stability.