Intraocular pressure and circulation at the disc in glaucoma

Intraocular pressure and visual field loss in primary angle closure and primary open angle glaucomas

AIM

To compare the correlation between visual field loss and the pretreatment intraocular pressure (IOP) in primary angle closure glaucoma (PACG) and primary open angle glaucoma (POAG).

METHODS

In a cross sectional observational study of 74 patients (43 PACG, 31 POAG), pretreatment IOP was measured at presentation, before treatment was initiated. The severity of visual field loss was assessed by AGIS score, mean deviation (MD), pattern standard deviation (PSD), and corrected pattern standard deviation (CPSD). Glaucomatous optic neuropathy was assessed from simultaneous stereo disc photographs.

RESULTS

There was a stronger correlation between pretreatment IOP and the extent of visual field loss in PACG subjects than in those with POAG for both MD (PACG: Pearson correlation coefficient (r) = 0.43, p = 0.002; r(2) = 0.19), (POAG: r = 0.21, p = 0.13; r(2) = 0.04) and AGIS score (PACG: r = 0.41, p = 0.003; r(2) = 0.17), (POAG: r = 0.23, p = 0.19; r(2) = 0.05 respectively). No such associations were seen for pattern standard deviation (PSD) or corrected pattern standard deviation (CPSD) in either group (p> 0.29). Both horizontal and vertical cup-disc ratio were well correlated with severity of field loss but not with presenting IOP for either diagnosis.

CONCLUSIONS

This is consistent with the hypothesis of a greater IOP dependence for optic nerve damage in PACG than POAG and, conversely, a greater importance of other, less pressure dependent mechanisms in POAG compared to PACG.

Effects of kallidinogenase on ocular tissue circulation in rabbits

The purpose of this study is to evaluate the effects of kallidinogenase, a tissue kallikrein, on tissue circulation in the optic nerve head (ONH), choroid and retina. Kallidinogenase (1.0 IU/kg) or saline was injected intravenously into urethane-anesthetized rabbits, and the normalized blur value (NB), a quantitative index of in vivo tissue blood velocity, was measured in the ONH, choroid and retina before and for 90 minutes after injection, using the laser speckle method. The difference in NB values in the kallidinogenase group was significantly higher compared with that in the control group in the choroid (p < 0.05) and retina (p < 0.05, ANOVA of repeated measurements). In the ONH, however, there was no significant difference between the kallidinogenase group and the control group except transient increment 10 min after drug administration (p < 0.01, unpaired t-test). On the other hand, systemic condition parameters and intraocular pressure showed no intergroup difference significantly except for a transient decrease in blood pressure and increase in pulse rate in the kallidinogenase groups. Kallidinogenase increased blood velocity, and probably blood flow, in the choroid and retina of rabbits.

Glaucoma: diagnosis and management

Glaucoma is the third most prevalent cause of global blindness, accounting for over 5 million blind. It is common in Western Countries; the estimated prevalence of primary open angle glaucoma rises from a total prevalence of 1.1% to approximately 3% of our population as it ages. Ethnicity affects both the risk of developing glaucoma and the outcome. It is an expensive disease both to detect and to treat. Recent scientific advances include elucidation of the genetic mechanism behind the disease and the study of haemodynamic and biochemical co-factors in the development of glaucomatous optic neuropathy, particularly in relation to the pathogenesis of normal tension glaucoma. Several new types of topical medication have recently been developed for use in glaucoma; both the impact of these therapies and their cost effectiveness remain to be evaluated. There are widely differing regimes which effectively treat glaucoma; some ophthalmologists prefer early surgical intervention whilst others reserve surgery for relatively advanced disease. All methods of current treatment rely on the reduction of intra-ocular pressure; as yet there is no medication which has been definitively proven to be either neuroprotective or to influence favourably optic nerve perfusion. Despite this, most sufferers of glaucoma are able to lead lives of quality. Increased community awareness of glaucoma, and earlier detection of the condition, will doubtless result in decreased morbidity due to glaucoma.