Inter-instrument agreement and influence of central corneal thickness on measurements with Goldmann, pneumotonometer and noncontact tonometer in glaucomatous eyes.

PURPOSE: This study was conducted to compare the intraocular pressure (IOP) measurements by the Goldman applanation tonometer (GAT), non contact tonometer (NCT) and the ocular blood flow (OBF) pneumotonometer in different IOP ranges in glaucomatous eyes. The effect of central corneal thickness (CCT) on IOP measurement in chronic glaucomatous eyes using the three different tonometers was also evaluated. MATERIALS AND METHODS: IOP measurements of 130 eyes of primary glaucoma patients were performed using GAT by an ophthalmologist while NCT and OBF-pneumotonometer measurements were performed by an experienced optometrist. The IOP values were compared amongst the three instruments in the three different IOP ranges (0-18 mmHg, > 18 to 25 mmHg, > 25 mmHg). CCT was also measured in all patients. RESULTS: The mean of paired difference between GAT and NCT was 0.9 +/- 3.1 mmHg while that between GAT and OBF-pneumotonometer was 0.3 +/- 3.4 mmHg. The OBF-pneumotonometer and NCT were more affected by corneal thickness (0.41 mmHg and 0.4 mmHg / 10 micro corneal thickness respectively) while GAT was the least affected by corneal thickness (0.3 mmHg / 10 micro corneal thickness) though the difference was not statistically significant ( P =0.42). CONCLUSION: With appropriate correction for corneal thickness the NCT and OBF-pneumotonometer can be used as reliably as GAT in following up glaucomatous patients.

Pulsatile ocular blood flow among normal subjects and patients with high tension glaucoma.

PURPOSE: To estimate pulsatile ocular blood flow (POBF) among normal subjects and to compare various parameters in eyes of primary open angle glaucoma with high intraocular pressure (IOP). METHODS: POBF was estimated in 95 eyes of 95 normal subjects above the age of 40 years and in 35 eyes of 35 primary open angle glaucoma patients using the OBF system (OBF Labs Ltd., UK). Correlation of age, gender, IOP, pulse amplitude, pulse volume and pulse rate with POBF was studied. POBF values were measured in glaucomatous patients before IOP control and one month later after control of IOP to < 22 mmHg. RESULTS: The mean POBF among normal subjects was 1382.2 +/- 413 ml/min (range 636-2291 m/min). Females had a significantly higher mean POBF (1512 +/- 347 ml/min) than males (1193 +/- 312 ml/min). The mean IOP among normal subjects was 12.6 mmHg and in glaucoma patients, 29.1 mmHg. Mean POBF in glaucomatous eyes with initially elevated IOP was 718.9 +/- 322.6 ml/min, which improved after IOP control to 1129 +/- 291 ml/min. IOP had a strong (P < .01) negative correlation with POBF (r = -0.667) CONCLUSIONS: POBF among eyes of normal subjects in this study is higher than reported among Caucasian eyes. Primary open angle glaucoma eyes with high IOP have significantly reduced ocular blood flow. Therapy aimed at lowering IOP has a positive effect onocular haemodynamics.

The normal optic nerve head on Heidelberg Retina Tomograph II.

PURPOSE: To study the characteristics of the optic nerve head using a scanning laser ophthalmoscope, the Heidelberg Retina Tomograph II (HRT II), in a normal population and to determine the specificity of HRT II diagnostic indices in the study population. METHODS: The optic nerve heads from 275 consecutive, randomly selected normal subjects were imaged on HRT II. Stereometric parameters were studied with respect to baseline variables such as age, gender, refractive error and disc size. The stereometric parameters and the results of Moorfields regression analysis (MRA) and discriminant function analysis were recorded. RESULTS: The average disc size in the population under study was 2.34 +/- 0.47 mm2. Age and gender had no significant effect on stereometric parameters. Myopic discs were larger than hypermetropic discs. MRA had a specificity varying between 85.5% and 98.2% depending upon the criteria used to define an abnormal disc. The specificity of MRA decreased with increasing disc size. The RB (R Bathija) and FSM (F S Mikelberg) discriminant functions had specificities of 96.4% and 87.3% respectively. CONCLUSIONS: Estimation of stereometric parameters of a normal disc can be used to indicate an abnormal one. Moorfields regression analysis and discriminant functions have a high specificity in our normal population; however caution must be exercised in interpreting the results for a disc area larger than 3 mm2.