Analysis of macular volume and thickness in primary open angle glaucoma suspects and patients with primary open angle glaucoma using optical coherence tomography

INTRODUCTION: Glaucoma is one of the leading cause of irreversible blindness in the developing countries and a major health problem in developed countries1. The early diagnosis of glaucoma and early detection of its progression are twin challenges the present generation ophthalmologists face4. WHO statistics indicate that glaucoma accounts for blindness in 5.1 million people i.e. 13.5% of global blindness. Since glaucomatous damage is irreversible, prevention of this injury before it occurs is the essential strategy available to those treating the disease. Primary open angle glaucoma is characterized by chronic progressive optic neuropathy developing in the presence of open angles with characteristic visual field defects and raised intra ocular pressure3. In glaucoma the essential pathologic process is the loss of retinal ganglion cells and their axons. Studies have shown that glaucomatous damage to the retinal nerve fiber layer precede functional loss by as much as 5 years. AIMS AND OBJECTIVES: To analyze and establish the structure functional relationship between OCT macular volume /thickness parameters in patients with POAG SUSPECTS and POAG CASES . To correlate macular thickness and RNFL thickness in primary open angle glaucoma suspects and primary open angle glaucoma patients using OPTICAL COHERENCE TOMOGRAPHY (OCT). MATERIALS AND METHODS: A prospective study to analyze and establish the structure functional relationship between OCT macular volume/thickness parameters in patients with POAG –SUSPECTS and POAG PATIENTS was undertaken in the department of glaucoma services , ARAVIND EYE HOSPITAL , MADURAI . The study was conducted between November 2004 and September 2005, during which period a total of 290 eyes of 146 patients were studied and analyzed. SUBJECTS INCLUSION CRITERIA: Patients in the age group of 14 -75 years. Patients with suspected POAG and patients with POAG diagnosed at the time of study or previously diagnosed as POAG patient. Open angles on gonioscopy using modified shaffer’s grading system. Patients with refractive errors-myopia less than 5 diopters , hypermetropia less than 3.5 diopters and astigmatism less than 2 diopters. Patients who were cooperative and willing for the study were included in the study. EXCLUSION CRITERIA Patients outside the age group specified in the inclusion criteria. All types of glaucoma other than POAG. All gross media opacities which interfere with the OCT imaging. Patients with retinal and macular diseases. DISCUSSION: This study was designed with the objective of analyzing the macular thickness and volume parameters in primary open angle glaucoma suspects (POAG Suspects) and primary open angle glaucoma (POAG) patients and establish the structure functional relationship between OCT macular volume / thickness parameters in POAG Suspects and POAG patients. The study also compared the macular thickness with RNFL thickness in its association with the disease and found that the macular thickness changes to be correlating well with changes in the retinal nerve fiber layer , hence represent a surrogate indicator of retinal ganglion cell loss. CONCLUSION: Macular retinal thickness as measured by OCT was capable of detecting glaucomatous damage and corresponded with peripapillary NFL thickness . Glaucoma is a complex multifactorial disorder characterized by a typical pattern of optic nerve damage and visual field loss that is usually but not always associated with elevated IOP . Accepted parameters for monitoring glaucoma include descriptions and photography of the optic disc appearance ( cup disc ratio), measurement of IOP, and periodic threshold perimetry. Advances in posterior segment imaging technology provides a means for generating structural data useful in monitoring eyes with glaucomatous optic nerve damage. Objective, quantitative measurements of optic nerve and surrounding RNFL generated with these technologies correlate with known characteristics of optic disc function and visual function. Based on our findings we do not recommend the routine use of OCT macular scanning alone for glaucoma detection unless there are ocular pathologies that prevent scanning of the peripapillary region. Conversely , because macular retinal thickness corresponds well with peripapillary NFL thickness , macular scanning can provide a confirmation of abnormalities detected by peripapillary OCT scans. Especially in subtle cases, particularly those with minimal or no perimetric findings, macular and peripapillary scans may reinforce each other in conforming the presence of early abnormalities