Correlation of structural and functional changes in primary open angle glaucoma (POAG) patients based on visual field and optical coherence tomography

• Author Details:   
• Krupali Raol ^*
• Ruchi Kabra
• Ronak Bhanat
• Riddhi Gajjar
• Rajvi Mehta

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Background: Primary open-angle glaucoma (POAG) is characterized by an open anterior chamber angle, glaucomatous optic nerve head (ONH) changes, visual field (VF) defect, and an intraocular pressure (IOP) more than 21 mm Hg on more than one occasion.

Aim & Objectives: Comparison of subjective and objective diagnosis of structural abnormality of optic nerve head caused in glaucoma patients by 90D lens on slit lamp v/s SD OCT based disc and RNFL changes and functional abnormality by visual field changes using standard automated perimetry (SAP). The Objective is to assess clinical cup/disc ratio, RNFL loss using SD OCT and visual field by perimetry, and the correlation of intraocular pressure (IOP) with all these variables, thereby identifying risk factors and aiding proper management, early diagnosis, grading severity and halting progression of primary open angle glaucoma.

Materials and Methods: Cross-sectional study at a primary care centre on 102 primary open angle glaucoma patients (180 eyes) visiting ophthalmology department for a period of 2 years.

All patients underwent visual assessment, IOP measurement by Goldman applanation tonometer, gonioscopy, optic nerve head examination with slit lamp biomicroscopy using 90D lens, an optical coherence tomography (OCT) and visual field by perimetry.

Results: We observed a statistically significant correlation between clinical cup/disc ratio, increase in loss of RNFL thickness and probability of abnormal visual field.

CDR of 0.6 to 1.0 were observed, which statistically correlated with SD OCT CDR, (P=0.007). A statistically significant correlation between OCT and VF (P= 0.0183), of which inferior-temporal sector defect had a significant correlation with corresponding superonasal VF defect (P value=0.0048).

Conclusion: We observed that persistent higher levels of IOP were notably related to higher rates of progressive RNFL loss. The proportion and severity of scotoma increases as CD ratio increases along with an increase in loss of RNFL thickness.

Visual field analysis by automated perimeter is more specific as compared to SD-OCT, which is more sensitive.

Keywords: Glaucoma, Glaucomatous optic nerve head, Intraocular pressure, Visual field, Optical coherence tomography, Perimetry, Slit lamp biomicroscopy, CD ratio, Gonioscopy, RNFL, Goldman applanation tonometry.