Omar S. Punjabi

Dynamic contour tonometry: principle and use

Interindividual variability of central corneal thickness has been found to be a source of error for conventional Goldmann applanation tonometry. The dynamic contour tonometer represents a potentially new technology for non‐invasive and direct intraocular pressure (IOP) measurement, and has been proposed to accurately measure the true IOP irrespective of the corneal thickness. It is based on the principle that when the tip of the device exactly matches the contour of the cornea, the pressure measured by a transducer placed on its tip is an accurate indicator of the true IOP. This device is also capable of measuring the ocular pulse amplitude, a variable that has controversial significance in the diagnosis and management of glaucoma. Even though this technique seems to be very promising, further studies are required to conclusively determine the effectiveness of the dynamic contour tonometer in patients having an abnormal or irregular corneal contour.

Intraocular Pressure and Ocular Pulse Amplitude Comparisons in Different Types of Glaucoma Using Dynamic Contour Tonometry

Purpose: To compare the intraocular pressures (IOP) and ocular pulse amplitudes (OPA) in patients with different types of glaucoma, ocular hypertension (OHT), and normal controls (NC) using dynamic contour tonometry (DCT) and the goldmann applanation tonometry (GAT). Methods: 906 eyes of 501 adult patients in the following five groups were included in this cross-sectional study: primary open angle glaucoma (POAG), normal tension glaucoma (NTG), Pseudoexfoliative Glaucoma (PXG), OHT, and NC. The following tests were performed simultaneously during a single visit: IOP using DCT and GAT; OPA using DCT and central corneal thickness (CCT) using ultrasound pachymetry. Mixed effects regression models were used to compare the DCT and GAT IOP measurements in the five groups; the effect of CCT on IOP and the relationship between OPA and IOP within each group. Results: DCT consistently had higher IOP values than GAT in POAG, PXG, NTG, and controls (p < 0.001) but not in OHT (p = 0.84). DCT IOP did not change while GAT IOP showed a non-significant increase (p = 0.09) with increased corneal thickness in each group. OPA was found to be highest in OHT (3.61 mmHg) and lowest in the control group (2.86 mmHg) and significantly increased with IOP in all groups. Conclusions: DCT measures an IOP that is significantly higher than GAT IOP in glaucoma and control subjects but not in ocular hypertensives. Furthermore, the DCT may measure an IOP that is independent of the CCT, which may not be true for the GAT, which increases with the CCT. OPA was highest in OHT and may be affected by the IOP.

Tonometry Through the Ages

The definition of glaucoma has changed over the decades from a simple ocular pressure disease to a systemic disorder of multivariate etiology. Glaucoma may be defined for the individual eye as a chronic ocular disease with various underlying pathophysiologic disorders. However, elevated intraocular pressure (IOP) is still the most important risk factor for an untreated glaucomatous eye to progress to a more severe stage of the disease. As the main risk factor within therapeutic reach, IOP and its appropriate measurement deserve our ongoing interest. Not only has our understanding of glaucoma changed but also our approach to the measurement of the IOP. In this article we focus our attention on the various developments in tonometry from the simple force-tonometers of the late 19th century to the high-technology pressure tonometers that were recently introduced for clinical use.

Effect of statin drugs and aspirin on progression in open-angle glaucoma suspects using confocal scanning laser ophthalmoscopy

Purpose:  To determine the effect of statins and aspirin on the rate of progression of optic nerve parameters in open‐angle glaucoma (OAG) suspects, as defined by confocal scanning laser ophthalmoscopy (CSLO).

Does treated systemic hypertension affect progression of optic nerve damage in glaucoma suspects

Purpose: To evaluate whether treatment of systemic hypertension has an effect on progression of optic nerve parameters in glaucoma suspects using confocal scanning laser ophthalmoscopy. Methods: Two hundred eyes of 103 glaucoma suspect patients were included in this retrospective cohort study. Thirty one patients (of whom 59 eyes were included in the study) had systemic hypertension under treatment (based on medical history). The remaining 72 age-matched normotensive controls (of whom 141 eyes were included in the study) were not on blood-pressure-lowering medications. Each patient had a follow-up period of at least 4 years with a minimum of four Heidelberg retinal tomograph tests (one baseline and three follow-up scans). The slopes of progression of optic nerve head parameters with time were studied and compared between these two groups using mixed effects regression models. Results: Patients with systemic hypertension showed a statistically significant increase in cup area (slope 0.2, p = 0.03), cup-to-disk area ratio (slope 0.01, p = 0.007), and decrease in rim area (slope −0.4, p = 0.03), rim-to-disk area ratio (slope −0.01, p = 0.005), and global Retinal Nerve Fiber Layer (RNFL) thickness (p = 0.008) with time. The differences in slopes of progression of many parameters between hypertensives and normotensives were statistically significant. Conclusions: Systemic hypertension treated with hypotensive medications may be a risk factor for increased progression of optic nerve parameters in glaucoma suspects compared with age-matched normotensive subjects.

Repeatability of the multifocal visual evoked potentials in a clinical glaucoma setting

BACKGROUND To determine the reproducibility of the multifocal visual evoked potentials (mfVEP) test results in a clinical glaucoma setting, and the factors that affect variability. METHODS This was an observational case series study. The monocular mfVEP test, having a 58-sector, pattern-reversal dartboard array, was performed twice within 4 weeks in both eyes of 29 adult open-angle glaucoma (OAG) patients and suspects, using AccuMap Opera Software (ObjectiVision Pty Ltd, Sydney, Australia). The AccuMap severity index (ASI), the mean amplitude, and the individual amplitudes in each sector were compared between the 2 tests using intraclass correlations (ICCs). The effects of the severity of mfVEP field defects and signal-to-noise ratio (SNR) on the reproducibility of these variables were determined using the McNemar test and the Spearman rank correlation, respectively. RESULTS The average ICCs of the ASI and amplitudes in the 2 tests were 0.84 and 0.87, respectively. Two sectors in the right eye and 6 in the left eye had significant differences between the 2 tests (Wilcoxon signed-rank p < 0.05). Larger differences were observed in patients having lower SNR (Spearman p = 0.022). Forty-six of the 58 eyes stayed within the same diagnosis category on repeating the test (i.e., within normal limits or outside normal limits). INTERPRETATION Although there were some isolated examples of clinically significant differences on repeating the mfVEP test in our patients, our results suggest overall good repeat reliability. The variability of the test was higher in patients having high noise levels during the test.