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Abstract #51981 Published in IGR 14-4
The relationship between measurement method and corneal structure on apparent intraocular pressure in glaucoma and ocular hypertension
Nessim M; Mollan SP; Wolffsohn JS; Laiquzzaman M; Sivakumar S; Hartley S; Shah SContact Lens and Anterior Eye 2013; 36: 57-61
PURPOSE: To analyse the relationship between measured intraocular pressure (IOP) and central corneal thickness (CCT), corneal hysteresis (CH) and corneal resistance factor (CRF) in ocular hypertension (OHT), primary open-angle (POAG) and normal tension glaucoma (NTG) eyes using multiple tonometry devices. METHODS: Right eyes of patients diagnosed with OHT (n=47), normal tension glaucoma (n=17) and POAG (n=50) were assessed. IOP was measured in random order with four devices: Goldmann applanation tonometry (GAT); Pascal(®) dynamic contour tonometer (DCT); Reichert(®) ocular response analyser (ORA); and Tono-Pen(®) XL. CCT was then measured using a hand-held ultrasonic pachymeter. CH and CRF were derived from the air pressure to corneal reflectance relationship of the ORA data. RESULTS: Compared to the GAT, the Tonopen and ORA Goldmann equivalent (IOPg) and corneal compensated (IOPcc) measured higher IOP readings (F=19.351, p<0.001), particularly in NTG (F=12.604, p<0.001). DCT was closest to Goldmann IOP and had the lowest variance. CCT was significantly different (F=8.305, p<0.001) between the 3 conditions as was CH (F=6.854, p=0.002) and CRF (F=19.653, p<0.001). IOPcc measures were not affected by CCT. The DCT was generally not affected by corneal biomechanical factors. CONCLUSION: This study suggests that as the true pressure of the eye cannot be determined non-invasively, measurements from any tonometer should be interpreted with care, particularly when alterations in the corneal tissue are suspected.
Birmingham and Midland Eye Centre, City Hospital, Birmingham B18 7QH, UK.
Full articleClassification:
6.1.3 Factors affecting IOP (Part of: 6 Clinical examination methods > 6.1 Intraocular pressure measurement; factors affecting IOP)
2.2 Cornea (Part of: 2 Anatomical structures in glaucoma)
