Researchers from the Department of Ophthalmology at the University of Toyama, Japan, compared the fluctuation of intraocular pressure in normal-tension glaucoma patients and individuals without glaucoma. They obtained continuous IOP values using a Sensimed Triggerfish contact lens sensor.

The eyes of 12 nonglaucoma subjects and 14 NTG patients were examined. In all 26 subjects, IOP fluctuation was measured continuously for 24 hours with the Triggerfish. The range of IOP fluctuation was analyzed, and cutoff level of IOP fluctuation was calculated using receiver operating characteristic curve analyses.

The mean IOP in the NTG eyes was 11.5 ±2.4 mmHg, and in the nonglaucoma eyes it was 12.7 ±2.0 mmHg, a statistically insignificant difference (p=0.175). The 24-hour range of IOP fluctuations in the NTG group was significantly larger than that of the nonglaucoma group, however (p=0.007). The percentage of NTG patients who had the peak time of IOP fluctuation during nocturnal sleep was 57.1 percent, whereas the corresponding rate for the nonglaucoma eyes was 91.7 percent.

The range of IOP fluctuations was larger in the eyes with NTG than in the nonglaucoma eyes. This larger fluctuation might be one of the factors underlying the aggravation of the visual field by NTG. Measurements of 24-hour continuous IOP might be a useful way to distinguish NTG from nonglaucoma eyes, researchers say.

J Glaucoma 2017;26:195-200
Tojo N, Abe S, Ishida M, Yagou T, Hayashi A.

Tomography Systems in Corneas with Keratoconus
In this reliability analysis of the Orbscan II, Pentacam HR and Galilei tomography systems, researchers from Auckland, New Zealand, studied the repeatability and agreement of keratometry and pachymetry measurements obtained using these three tomographers in eyes with keratoconus. The researchers looked at 50 eyes of 50 patients with keratoconus. The observational procedure focused on: steep keratometry; flat keratometry; central corneal thickness; and thinnest corneal thickness.

Repeatability was assessed using within-subject standard deviation, coefficient of variation and intraclass correlation coefficient. Bland-Altman plots and 95 percent limits of agreement (mean difference ±1.96 multiplied by standard deviation) were used to evaluate agreement between device pairs.

For all studied parameters, ICC was >0.97, with the least repeatable measurements obtained using Orbscan II. Mean steep keratometry values were similar while mean flat keratometry values were significantly different among all devices. The Galilei and Pentacam HR had the lowest 95 percent LoA for both CCT and TCT. There were no significant differences in mean CCT between Galilei and Pentacam HR. Mean Orbscan II CCT measurements weren’t significantly different overall but had wide 95 percent LoA with Pentacam HR (-47.95 to 58.09 μm) and Galilei (-43.70 to 53.91 μm). Mean Orbscan II CCT measurements were significantly lower when an acoustic factor of 0.92 was applied (-33.6 μm vs Pentacam HR, p<0.001; -33.6 μm vs Galilei; p<0.001).

The researchers say that keratometric and pachymetric measurements of keratoconic eyes obtained by Galilei, Orbscan II and Pentacam were disparate. Although overall repeatability was high for all instruments, measurements were less repeatable with Orbscan II in comparison to Pentacam HR and Galilei.

Am J Ophthalmol 2017;175:122-128
Meyer J, Gokul A, Vellara H, Prime Z, McGhee C.