Contribution and significance of Heidelberg retinal tomography II in diagnostics of ocular hypertension and its conversion into primary open-angle glaucoma

Abstract

Background/Aim. A term 'ocular hypertension' is used when IOP is found to be > 21 mmHg on two consecutive occasions, in the absence of detectable glaucomatous damage. The aim of this study was to determine the significance and contribution of Heidelberg Retinal Tomography II (HRT II) results that show very early, subtle changes in retinal neurofibre layers (RNFL) in the optic nerve head that are specific for glaucoma itself (the loss of neuroretinal rim area and an increase of Cup/Disc ratio), but are not possible to register by an ophthalmoscope. Also, when the results of the functional tests remain unchanged, that confirms the conversion of ocular hypertension into glaucoma. Methods. During a 5-year study period (2002-2007), 29 patients with ocular hypertension were examined. The frequency of control examinations, based on the presence of risk factors for glaucoma development, was 3-6 months. The examination also included IOP measurements with Goldmann Applanation Tonometry (GAT), central corneal thickness (CCT) determination by pachymetry, the examination of chamber angle using indirect gonioscopy, visual field tests by computerized perimetry and also papillae nervi optici (PNO) examination by using HRT II. The application of HRT II enables a great number of stereometric parameters of optic disc, the most important being the rim area and Cup/Disc (C/D) ratio, which was followed during the control examination by each segment, as well as PNO in global. Results. In the examination period, three cases of conversion of ocular hypertension into a primary open-angle glaucoma were found. In the group of patients with ocular hypertension, HRT II results after six months did not show a significant increase in C/D ratio. No significant loss of rim area or rim volume was found either. In three cases of conversion, HRT II results after 3 months showed an increase of C/D ratio and also a significant loss in rim volume at first examination (0.413) comparing to the last one. Conclusion. In diagnosing ocular hypertension and its conversion to glaucoma, HRT II is used for quantitative evaluation of retinal topography and for quantitative monitoring of topographical changes, especially regarding the increase of C/D ratio and loss of rim volume tissue, which enables to see and register subtle structural changes in optic nerve head and RNFL that are so characteristic for glaucoma, which cannot be seen by an ophthalmoscope. With these results, according to risk factors for glaucoma, one can confirm the diagnosis of ocular hypertension and its conversion to primary open-angle glaucoma. In this study HRT II revealed conversion of ocular hypertension into glaucoma in 10% of the patients