A Study to Analyse the Significance of Pressure-To-Cornea Index in Pseudoexfoliation Eyes with and without Glaucoma

INTRODUCTION: Normal human central corneal thickness (CCT) varies between a range of 490 μm to 560 μm. Whereas the intraocular pressure (IOP) measured by the gold standard method ‘Goldmann Applanation Tonometry’ is based on the assumption that CCT is 520 μm. Pressure-To-Cornea Index(PCI) was introduced to overcome the error in correction of IOP according to the CCT by various nonstandardized formulae, and also to integrate IOP and CCT as a single risk factor for glaucoma. In pseudoexfoliation eyes, CCT remains to be a highly variable factor irrespective of the presence of glaucoma, which in turn will affect the IOP in extreme CCT values. AIMS AND OBJECTIVES: 1. To integrate IOP and CCT as a single risk factor in the form of PCI for various IOP levels. 2. To find out the distribution of PCI in patients with and without pseudoexfoliation (PXF) and to find out whether PCI can be taken as a predictor for open angle glaucoma (OAG) secondary to pseudoexfoliation. MATERIALS AND METHODS: This study was conducted among 90 eyes of patients above 40 years of age (30 PXF eyes without glaucoma(PXS), 30 eyes with glaucoma secondary to pseudoexfoliation syndrome (PXG), 30 normal subjects with no evidence of glaucoma or pseudoexfoliation), attending our department as outpatient as well as inpatient to the wards of our Govt. Rajaji Hospital, Madurai. METHODOLOGY: A detailed evaluation including history, visual acuity, slit lamp examination, gonioscopy, IOP, CCT, fields and dilated fundus examination were performed. Diagnosis of PXS was based on the presence of PXF material over the pupil or lens or both, with normal IOP, normal fields and no optic disc changes and PXG with increased IOP with glaucomatous optic disc changes and field defects. Diagnosis PXS and PXG are based on the IOP corrected by Ehlers formula, i.e, 0.7 mm Hg per 10μm difference in CCT. RESULTS: PXF patients were between 50 to 70 yrs, of which 41.67% were between 50 – 60 years and 58.33% between 60 – 70 years of age. 37 were males (61.67% ) and 23 females (38.33%) among the 60 patients with a male preponderance. PXF deposition was unilateral in 35(58.33%) and bilateral in 25 patients (41.67% ). 53.33% had nuclear sclerosis, 41.67% had immature cataract and 5% had minimal lens changes. PXF material is seen in lens in 25 (41.67%), pupil in 8 (30%) and both in 17 (28.33%) patients. Mean IOP in the normal, PXS and PXG group 17.5, 18.133 and 22. 867 mmHg respectively, which differed significantly. The mean CCT in normals, PXS and PXG group was 547 μm, 522 μm and 500 μm respectively. There was a statistically significant difference between the normal and PXS groups, and PXS and PXG groups with higher mean value in normal than PXS group which is higher than the PXG group. Mean PCI in normal subjects, PXS and PXG group was 107.074, 127.899, 182. 654 with S.D. of 10.845, 10.295, 28.700 respectively. There was a highly significant difference (p < 0.001) between the normal and PXS group, and PXS and PXG group. CONCLUSION: Since high IOP and low CCT acts as independent risk factors for glaucoma, PCI an index between IOP and CCT acts as a unified risk factor and indicator of glaucoma in PXF patients. Increased PCI values in PXG patients can also indicate the severity of glaucoma and also the better indicator of the response to treatment. High PCI in eyes with pseudoexfoliation syndrome without glaucoma can act as a predictor for glaucoma, even before increase in IOP or optic disc/ field changes. This shows the individual susceptibility of the person with PXS to develop secondary glaucoma. Hence, PCI can be useful for the consulting ophthalmologist to have a close follow up and for early diagnosis and treatment of pseudoexfoliative glaucoma, so that prevent further damage to optic nerve head