Is the observed lowering of intraocular pressure due to treatment?

Objective:

Use Bayes'' theorem to estimate the intraocular pressure (IOP) lowering effect of medical treatment initiated for glaucoma and determine if IOP comparisons to the baseline IOP of the same eye is clinically useful.

Materials and Methods:

The probability that treatment with prostaglandin is responsible for an observed 20% decrease in IOP with prostaglandin treatment was calculated using Bayes'' theorem using the following available information: the probability of a 20% decrease in IOP given treatment with prostaglandin, the probability of a treatment effect using prostaglandin and the overall probability of a 20% decrease in IOP. The calculations were repeated to account for a possible 2 mmHg overestimation of effect caused by measurement error in performing applanation tonometry.

Results:

The probability that treatment is responsible for an observed 20% decrease in IOP following initiation of treatment with a prostaglandin was 99%. After adjusting for measurement error this probability was 98%. Obtaining two IOP measurements marginally increased the probability.

Conclusion:

Following initiation of treatment with prostaglandin, Bayes'' theorem allows us to infer that treatment effect is the most likely explanation for an observed 20% decrease in IOP from the baseline; this inference remains even after adjusting for known measurement error. The high probability of a treatment effect is due to the high prior odds of treatment effect and the high likelihood ratio for prostaglandin producing such an effect. If data is available, similar calculations can be used for other percentage decreases, other medications and for the monocular trial.     

Which endpoint: mean intraocular pressure or proportion of successful patients?

A reduction in intraocular pressure in clinical trials can be determined through the mean intraocular pressure, through the proportion of patients who have the intraocular pressure reduced to a specific target intraocular pressure, or both. Since both these possible endpoints measure the shift of 2 intraocular pressure distributions, we recommend that only one of them be tested. In general, testing the difference between mean-values is much more efficient than testing the difference between proportions. However, proportions of successful patients are valuable in showing the clinical implication of a reduction in mean intraocular pressure, particularly when evaluating a moderate pressure reduction. The effect of a small mean intraocular pressure reduction on the probability to reach the target intraocular pressure is pointed out, particularly the fact that it can be substantial even if the mean reduction is smaller than the measurement error.     

【In Press】 Efficacy of selective laser trabeculoplasty following incisional glaucoma surgery

AIM: To evaluate the efficacy of selective laser trabeculoplasty (SLT) in glaucomatous eyes with previous incisional glaucoma surgery. METHODS: A retrospective cohort of eyes that underwent SLT at a single institution from 2013-2015 were followed for 1y. Reduction in intraocular pressure (IOP) following SLT was evaluated in eyes with prior trabeculectomy with ExPress mini shunt (Alcon, Ft Worth, TX), Ahmed valve (New World Medical, Cucamonga, CA), or combined phacoemulsification-trabeculectomy. A control group was included with eyes without prior surgery that underwent SLT. Success was defined as >20% drop in IOP from pre-SLT baseline. RESULTS: One-hundred and six eyes were included with 53 in both the prior glaucoma surgery (PGS) and no prior glaucoma surgery (NPGS) groups. Mean pre-SLT IOP was 19.2±4.3 and 20.6±6.0 mm Hg for PGS and NPGS groups, respectively (P=0.17). Both groups produced statistically significant IOP reductions at 1 and 6mo (P<0.04). At 6 months, mean IOP reduction reached 7.3% and 10.8% for the PGS and NPGS groups, respectively (P=0.42). Overall, 27.9% and 31.7% of eyes in PGS and NPGS groups met success criteria at 1y (P=0.70). In the PGS group, eyes with baseline IOP ≥21mm Hg had IOP reductions of 18.1% (P<0.001), 16.7% (P<0.01), and 8.4% (P=0.31) compared to eyes with baseline IOP <21 mm Hg who had IOP reductions of 2.3% (P=0.39), 3.4% (P=0.19), and 1.1% (P=0.72) at 1 month, 6 months, and 1 year, respectively. CONCLUSION: SLT is efficacious in eyes with prior incisional glaucoma surgery and results in similar IOP reductions compared to eyes without prior glaucoma surgery. A larger IOP reduction is observed following SLT in eyes with higher pre-SLT IOP.     

Does the use of trypan blue during phacoemulsification affect the intraocular pressure?

Objective: The purpose of the study was to evaluate the effect of trypan blue on intraocular pressure (IOP) after small-incision cataract surgery.Design: Prospective, randomized study.Participants: Fifteen patients (30 eyes) with bilateral, dense, age-related cataracts.Methods: Patients with glaucoma, ocular hypertension, exfoliation, pigment dispersion syndrome, history of uveitis, recent use of topical or systemic steroids, and previous ocular surgery were excluded. The patients were randomly assigned to receive trypan blue during cataract surgery for enhancing capsulorrhexis in 1 of their eyes, while in the other eye, trypan blue was not used. Cataract surgery was performed in an identical fashion in both eyes, with a sutureless posterior limbal incision, phacoemulsification, and implantation of a foldable intraocular lens. The same viscoelastic (sodium hyaluronate) was used in all cases and was thoroughly aspirated at the end of the procedure. All patients received a single dose of 250 mg acetazolamide 8 hours after surgery. No other antiglaucomatous agent was used during surgery or postoperatively. The intraocular pressure (IOP) was measured preoperatively and at 24 hours, 1 week, 1 month, and 3 months postoperatively.Results: IOP values were similar in both groups at all 4 postoperative measurements. There was no statistically significant difference in postoperative IOP values between the eyes in which trypan blue was used and the control eyes.Conclusions: The use of trypan blue during small-incision cataract surgery does not have any effect on IOP during the immediate and early postoperative period.     

Evaluation of the effect of daily activities on intraocular pressure in healthy people: is the 20 mmHg border safe?

Purpose

The aim of this prospective study was to evaluate the intraocular pressure (IOP) variations during daily activities such as reading, speaking and carrying in regard to investigating whether an elevation or decrease exists.

Subjects and methods

Forty-four eyes of 44 healthy subjects were evaluated. The IOP was measured in relaxation and after reading, speaking and carrying a shopping bag for 5 min on different days, respectively. The subjects rested for 15 min between the activities. Mean initial IOP levels were compared with mean IOP levels after reading, speaking and carrying a shopping bag with paired t test. A p value of 0.05 was considered as statistically significant.

Results

We observed no changes in mean IOP after reading (p = 0.188). Mean IOP was increased after speaking and carrying compared with mean basic IOP (p = 0.001 and p = 0.001, very significant, respectively). The mean IOP began to decrease 15 min after speaking and carrying and came back to the baseline values one hour later.

Conclusions

The IOP is not stable during daily activities. Simple actions such as carrying or speaking have an increasing effect on IOP. This should be taken into consideration in glaucoma patients during control measurements, especially in patients in whom the IOP was near to the 20 mmHg border.

     

Does patient comfort influence the choice of tonometer for the measurement of intraocular pressure?

The purpose of this study was to compare patient comfort and preference between the use of Icare tonometer and Goldmann applanation tonometer for the measurement of intraocular pressure (IOP). This was a prospective study carried out at the Eye clinic of the University College Hospital, Ibadan on volunteers aged 18 years and above. Demographic information of the participants was collected using a proforma. All participants had Icare tonometry and Goldmann applanation tonometry (GAT) performed on them in sequence within a 15-min period. After the measurements, participants were asked to report their assessment of the level of comfort with each method and to state their preferred choice for IOP measurement. One hundred subjects participated in the study; 45 (45 %) were males, and the mean age was 47.1 (± 17.4) years. Forty-three subjects (43 %) reported that Icare was either much more comfortable or more comfortable than GAT, while 31 (31 %) stated that Goldmann applanation was either much more or more comfortable. Twenty-six participants (26 %) reported that the level of comfort was the same with the two instruments. With regard to which of the instruments will be preferred for IOP check at another clinic visit, 53 (53 %) of the respondents preferred the Goldmann applanation tonometer. Some of the participants preferred GAT because they believed it was more sophisticated, while the main reported reason for preferring Icare was the stinging sensation of the anesthetic eye drop when using GAT. Although more participants reported the Icare tonometer to be more comfortable, the Goldmann tonometer was preferred by majority of the respondents.     

Does the site of filtration influence the medium to long term intraocular pressure control following microtrabeculectomy in low risk eyes?

AIMS: To evaluate the influence of varying surgical site on the medium to long term intraocular pressure (IOP) control in patients undergoing unenhanced small flap trabeculectomy (microtrabeculectomy) in eyes at low risk of failure. METHODS: A retrospective non-concurrent analysis was performed on two cohorts of patients who underwent unenhanced microtrabeculectomy at different sites by a single surgeon (SAV). The first cohort of eyes was part of a trial to study the astigmatic effect of microtrabeculectomy (results published elsewhere) and all had flaps centred at the 12 o'clock meridian (superior flaps). The second cohort consisted of eyes with flaps created on either side of the 12 o'clock-that is, superonasal in left eyes and superotemporal in right eyes. All case notes were reviewed for the preoperative and presenting IOPs, the number and duration of antiglaucoma medication use preoperatively and, postoperatively, any intraoperative, early, or late postoperative complications. All IOPs measured at 6 months and then yearly intervals were recorded. The baseline characteristics and IOPs at each follow up were compared between the eyes with the superonasal and superotemporal flaps of the non-12 o'clock group against those with superior flaps in the 12 o'clock group up to a maximum of 72 months. Survival was assessed by the site of microtrabeculectomy, with failure considered as any IOP above 22 and 15 mm Hg with or without medications. RESULTS: All patients had a minimum follow up of 12 months and 12/17 patients in the 12 o'clock group and 17/28 in the non-12 o'clock group completed the full follow up of 72 months. The IOPs at all points in time were lower in the left eyes with superonasal flaps compared to both the superior and the superotemporal groups. This difference was statistically significant between the three groups to the end of 4 years (p = 0.001) and remains clinically significant thereafter with the mean last recorded IOPs of 15.9, 12.4 (p = 0.03), and 14.3 mm Hg in the superior, superonasal and superotemporal groups respectively, with a smaller mean number of drops in the non-12 o'clock group. Kaplan-Meier curves showed a significantly better outcome for the cutoff IOP of 15 mm Hg in the superonasal group (p = 0.003) compared with both the other groups. CONCLUSION: Eyes with superonasal flaps achieve and maintain lower IOPs when compared with both the superior and superotemporal flaps. The results suggest that, when a low target IOP is desired, the site of surgery in an unenhanced filtering procedure should be superonasally sited.     

The influence of δ9-Tetrahydrocannabinol on intraocular pressure in the anaesthetized cat

⁹-Tetrahydrocannabinol (⁹-THC) was injected both intravenously and into the brain stem via the left vertebral artery. Contrary to results obtained with clonidine, neither the fall in intraocular pressure (IOP), nor the arterial hypotension induced by ⁹-THC, were enhanced after the central administration of the drug. For clonidine, a central mechanism underlying the ocular hypotensive effect has recently been proposed. This suggestion is based upon the enhanced fall in IOP after central administration of clonidine. The pontomedullary area is considered to be the main initial target of this drug. Obviously, the IOP-lavering mechanism of ⁹-THC is different from that of clonidine.     

Changes in intraocular pressure after intraocular eye surgery—the influence of measuring technique

AIM: To investigate the changes in intraocular pressure (IOP) before and after intraocular surgery measured with Goldmann applanation tonometry (GAT) and pascal dynamic contour tonometry (PDCT), and assessed their agreement. METHODS: Patients who underwent trans pars plana vitrectomy (TPPV) with or without cataract extraction (CE) were included. The IOP was measured in both eyes with GAT and PDCT pre- and postoperatively, where the non-operated eyes functioned as control. RESULTS: Preoperatively, mean IOP measurements were 16.3±6.0 mm Hg for GAT and 12.0±2.8 mm Hg for PDCT for the operated eyes. Postoperatively, the mean IOP dropped to 14.3±5.6 mm Hg for GAT (P=0.011) and rose up to 12.7±2.6 mm Hg for PDCT (P=0.257). Bland-Altman analysis showed a poor agreement between GAT and PDCT with a mean difference of 2.9 mm Hg preoperatively and 95% limits of agreement ranging from -3.2 to 9.0 mm Hg. Postoperatively, the mean difference was 1.2 mm Hg with 95% limits of agreement ranging from -8.3 to 10.7 mm Hg. There were no significant differences between the TPPV and TPPV+CE group, except when measured with PDCT postoperatively (P=0.012). CONCLUSION: The IOP is reduced after surgery when measured with GAT and remained stable when measured with PDCT. However, the agreement between GAT and PDCT is poor. Although PDCT may be a more accurate predictor of the true IOP, it seems less suitable for daily use in the clinical practice.     

Cataract,phacoemulsification and intraocular pressure: Is the anterior segment anatomy the missing piece of the puzzle?

Cataract extraction is a safe and effective surgery that has a lowering effect on the intraocular pressure. The specific mechanisms for this effect are still unclear. A direct inflammatory effect on the trabecular meshwork, alteration of the blood aqueous barrier, changes in the ciliary body and mechanical changes of the anterior segment anatomy are the key to understand cataract surgery and it's effects on aqueous humor dynamics. Additionally, with the advent of AS OCT, changes in the anterior segment of the eye have been studied and several parameters (such as lens vault, angle opening distance and anterior chamber depth) have been identified as predictors of intraocular pressure change. In eyes with narrow angles there is a greater drop in intraocular pressure after cataract surgery and it is correlated with parameters related to anterior chamber space. It is safe to affirm that cataract surgery is an important part of the modern glaucoma treatment and evidence should be analyzed as part of a bigger picture in order to more accurately understand its clinical relevance.     

Reducing intraocular pressure: is surgery better than drugs?

Reducing IOP is presently the evidence based, most accepted and most practised therapeutical approach for glaucoma patients. Currently topical ocular hypotensive medications, with its different classes, as well as filtering surgery (trabeculectomy and non-penetrating glaucoma surgery) are in the forefront of therapeutic modalities for IOP reduction. This article looks at the potential advantages and disadvantages of topical medications versus filtering surgery. It does not directly address the question of initial treatment of glaucoma, or what is the better treatment of glaucoma, as other review articles had, but rather looks in a more specific on the pros and the cons of each in relation to IOP reduction. In other words this article deals with the situation once the decision has been made to reduce IOP.