Six week safety study of 2% MK-927 administered twice daily to ocular hypertensive volunteers

Mixed treatment comparison of repeated measurements of a continuous endpoint: an example using topical treatments for primary open-angle glaucoma and ocular hypertension

Mixed treatment comparison (MTC) meta-analyses estimate relative treatment effects from networks of evidence while preserving randomisation. We extend the MTC framework to allow for repeated measurements of a continuous endpoint that varies over time. We used, as a case study, a systematic review and meta-analysis of intraocular pressure (IOP) measurements from randomised controlled trials evaluating topical ocular hypotensives in primary open-angle glaucoma or ocular hypertension because IOP varies over the day and over the treatment course, and repeated measurements are frequently reported. We adopted models for conducting MTC in WinBUGS (The BUGS Project, Cambridge, UK) to allow for repeated IOP measurements and to impute missing standard deviations of the raw data using the predictive distribution from observations with standard deviations. A flexible model with an unconstrained baseline for IOP variations over time and time-invariant random treatment effects fitted the data well. We also adopted repeated measures models to allow for class effects; assuming treatment effects to be exchangeable within classes slightly improved model fit but could bias estimated treatment effects if exchangeability assumptions were not valid. We enabled all timepoints to be included in the analysis, allowing for repeated measures to increase precision around treatment effects and avoid bias associated with selecting timepoints for meta-analysis.The methods we developed for modelling repeated measures and allowing for missing data may be adapted for use in other MTC meta-analyses.

Human corneal thickness and its impact on intraocular pressure measures: a review and meta-analysis approach

We determined the "normal" central corneal thickness (CCT) value in human corneas based on reported literature values for within-study average CCT values, and used this as a reference to assess the reported impact of physiological variables (especially age and diurnal effects), contact lens wear, pharmaceuticals, ocular disease, and ophthalmic surgery on CCT. With the expected CCT and its variance defined, it should be possible to determine the potential impact of differences in CCT in intraocular pressure (IOP) assessments, especially by applanation tonometry, using a meta-analysis approach. Some 600 sets of CCT data were identified from the worldwide literature over the period of 1968 through mid-1999, of which 134 included IOP measures as well. The within-study average CCT values and reported variance (SD) was noted along with the number of eyes and any special characteristics, including probable ethnic origin of the study subjects. Various sets of data were subjected to statistical analyses. From 300 data sets from eyes designated as normal, the group-averaged CCT was 0.534 mm. From 230 data sets where interindividual variance was reported, the group-averaged CCT was 0.536 mm (median 0.536 mm; average SD of 0. 031 mm, average coefficient of variation = 5.8%). Overall, studies using slit-lamp-based pachometry have reported marginally lower CCT values (average 0.530 mm, average SD 0.029 mm) compared to ultrasound-based studies (average 0.544, average SD 0.034 mm), which perhaps reflects the type of individual studied (non-surgical vs. pre-surgical patients) rather than the technique itself. A slight chronological increase in reported average CCT values (approximately 0.006 mm/decade) was evident, but a substantial chronological increase was evident for ultrasound pachometry studies (approximately 0.015 mm/decade). Within the meta-analysis-generated average and variance, age had no obvious impact on CCT measures for *whites, although an age-related decline in CCT is evident for non-whites. Any diurnal effects are likely concealed within the expected variance in CCT. Contact lens wear and pharmaceuticals generally produced changes in CCT that were well within the expected variance in CCT. Of the ocular diseases, only those associated with collagen disorders (including keratoconus) or endothelial-based corneal dystrophies (e.g., Fuchs) were likely to result in decreases or increases, respectively, of CCT beyond the normal variance. Routine contact lens wear and diseases such as diabetes seem unlikely to produce changes in CCT of a magnitude that would justify pachometry as a monitoring method beyond routine slit-lamp evaluation. Increases in CCT beyond the expected variance were reported after a range of intraocular surgeries (cataract operations, penetrating keratoplasty), whereas photorefractive surgery produces a measurable decrease in CCT. A meta-analysis of possible association between CCT and IOP measures of 133 data sets, regardless of the type of eyes assessed, revealed a statistically significant correlation; a 10% difference in CCT would result in a 3. 4 +/- 0.9 mm Hg difference in IOP (P </= 0.001, r = 0.419). The observed phenomenon was much smaller for eyes designated as healthy (1.1 +/- 0.6 mm Hg for a 10% difference in CCT, P = 0.023, r = 0. 331). For eyes with chronic diseases, the change was 2.5 +/- 1.1 mm Hg for a 10% difference in CCT (P = 0.005, r = 0.450), whereas a substantial but highly variable association was seen for eyes with acute onset disease (approximately 10.0 +/- 3.1 mm Hg for a 10% difference in CCT, P = 0.004, r = 0.623). Based on the meta-analysis, normal CCT in white adults would be expected to be within +/-11.6% (+/-2 SD) of 0.535 mm, i.e., 0.473-0.597 mm (95% CI, 0.474-0.596). The impact of CCT on applanation tonometry of healthy eyes is unlikely to achieve clinical significance, but for corneas of eyes with chronic disease, pachometry should be performed if the tonometry reveals IOP readi

Dorzolamide: development and clinical application of a topical carbonic anhydrase inhibitor

Systemic carbonic anhydrase inhibitors are among the most powerful agents to lower intraocular pressure. Unfortunately, their use is frequently accompanied by undesired side effects. Some are due to the relatively large amounts of drug that have to be systemically administered to inhibit the carbonic anhydrase in the ciliary processes. Recently, dorzolamide, a topical carbonic anhydrase inhibitor, has become commercially available for clinical use. This article reviews the development of topical carbonic anhydrase inhibitors with special reference to dorzolamide. When administered three-times daily, dorzolamide lowers intraocular pressure in a clinically useful manner. Ocular side-effects include frequent stinging and burning and allergy can develop. Systemic side effects have not been observed that could definitively be related to inhibition of extraocular carbonic anhydrase. Blood dyscrasias have not yet been observed. Absence of cardiovascular and pulmonary side effects, as can occur with beta adrenergic antagonists, and lack of pupillary and accommodative stimulation, as occur with cholinergic agonists, might make dorzolamide first-line medical treatment for elevated intraocular pressure.

Pharmacological advances in the treatment of glaucoma

Glaucoma is a potentially blinding disease. The goal of glaucoma therapy is to reduce intraocular pressure to a predetermined target level. There are currently 5 classes of compounds used for the medical management of glaucoma. Four classes that appear promising for the long term management of glaucoma are in different phases of clinical investigation, and include the topically active carbonic anhydrase inhibitors, selective alpha 2-adrenergic agonists, prostaglandins and ethacrynic acid. The topically active carbonic anhydrase inhibitor dorzolamide (MK-507) is effective and well tolerated in clinical trials of up to 1 year's duration. Animal studies have demonstrated that this drug lowers intraocular pressure by reducing aqueous humour formation. The selective alpha 2-adrenergic agonists, brimonidine and apraclonidine, have been shown to be effective in reducing intraocular pressure in the short term. Long term effectiveness of these agents is under investigation. Prostaglandins (PG) of the PGF2-alpha isopropylester series caused marked reductions of intraocular pressure in laboratory and clinical trials. The newest prostaglandin analogue, latanoprost (PhXA41), effectively lowered intraocular pressure and was well tolerated in clinical trials of up to 4 weeks' duration. Prostaglandins reduce intraocular pressure by enhancing uveoscleral outflow. Ethacrynic acid enhanced traditional outflow facility and lowered intraocular pressure when applied topically or intracamerally in laboratory studies and clinical trials. Corneal adverse effects of ethacrynic acid have been noted. Reformulation of ethacrynic acid ointment may resolve this problem. These 4 classes of compounds will enhance our options for the medical management of glaucoma. They may be used instead of or in combination with some of the drugs currently in use, and may be better tolerated.