By Alan S. Crandall, MD
This retrospective study in the April/May issue of the Journal of Glaucoma found a significant correlation between corneal hysteresis (CH) and central corneal thickness (CCT), and that CH was the corneal parameter most strongly associated with visual field (VF) progression. While CH is not a commonly used technique, this study finds it as productive as CCT. The results suggest that CH may add value to follow-up, although continued studies are needed to help define which patients are at increased risk for progression.
The authors conducted this study to determine the relationship between CH and CCT and which of these parameters better correlates with VF progression in glaucoma patients. One hundred fifty-three patients (153 eyes) were included who underwent complete ophthalmic examination and tonometry using both the Goldmann applanation tonometer and the Ocular Response Analyzer and Z5 SITA Standard 24-2 VF tests. They underwent a mean of 8.5±3.4 VF tests and had a mean follow-up time of 5.3±2.0 years.
The mean global rate of VF change was -0.34±0.7 dB/y. Twenty-five eyes (16 percent) reached a progression endpoint. Progressing eyes had lower CCT (525.0 ± 34.2 vs. 542.3 ± 38.5 mm, P = 0.04) and lower CH (7.5 ± 1.4 vs. 9.0 ± 1.8 mmHg, P < 0.01) compared with nonprogressing eyes. CH and CCT correlated significantly (r = 0.33, P < 0.01). By multivariate analysis, peak IOP [odds ratio (OR) = 1.13 per mmHg higher, P < 0.01], age (OR = 1.57 per decade older, P = 0.03) and CH (OR = 1.55 per mmHg lower, P < 0.01) remained statistically significant.
The results showed that CH was lower in eyes with worse VF damage. The observation that VF mean deviation was not associated with progression favors an independent association between CH and VF deterioration, regardless of how severe VF was at baseline. The study also adds information regarding rates of VF change and CH, showing that glaucomatous eyes with low CH not only reach event-based progression endpoints but also progress more rapidly (in dB/y) than those with statistically normal CH.
The authors conclude that lower CH could be a marker of increased susceptibility of the optic disc to glaucomatous damage or may be the result of glaucomatous damage itself.
The main clinical implication of this study, they say, is that patients with low CH should undergo more careful surveillance, with more aggressive IOP reduction possibly indicated to prevent future VF worsening.