Effect of acute increases of intraocular pressure on corneal pachymetry in eyes treated with travoprost: an animal study

Latanoprost treatment differentially affects intraocular pressure readings obtained with three different tonometers

PURPOSE

To evaluate the apparent intraocular pressure (IOP) change observed after treatment with latanoprost in naive eyes of patients with primary open-angle glaucoma (POAG) or ocular hypertension (OHT) using Goldmann applanation tonometer (GAT), ocular response analyzer (ORA) and Corvis ST tonometry.

METHODS

Prospective observational cohort study. One eye from each of 59 newly diagnosed patients with POAG or OHT in our institution was analysed. IOP readings obtained using GAT, ORA and Corvis at baseline and after a 3-month period of treatment with latanoprost were compared. Additionally, pre- and post-treatment biomechanical corneal parameters provided by the Corvis tonometer were analysed.

RESULTS

There was no statistically significant difference between the apparent treatment-induced IOP reductions when GAT and ORA were compared (p > 0.05). In contrast, the treatment-induced IOP reduction recorded using the Corvis tonometer was significantly smaller compared to the apparent IOP reduction observed with GAT and ORA (p = 0.0001 for both comparisons). With respect to biomechanical corneal properties, statistically significant changes were found after 3 months of treatment with latanoprost for the first corneal applanation time (AT1) (p = 0.001), second corneal applanation time (AT2) (p = 0.001) and deformation amplitude (DA) (p = 0.0003).

CONCLUSION

Following a 3-month course of latanoprost, the apparent treatment-induced IOP reduction in previously naïve patients with POAG or OHT differed depending on the tonometer used. Certain corneal biomechanical parameters assessed using Corvis ST exhibited a significant change. The ocular hypotensive effect of prostaglandin analogues may be overestimated when chronically treated patients are measured using GAT or ORA.

Effect of Acute Increases in Intraocular Pressure on Corneal Pachymetry in Rabbit Eyes Treated with Timolol Maleate

Objective:

To evaluate in an in vivo rabbit model, the effect of topical timolol maleate therapy on the central corneal thickness response to acute intraocular pressure increases.

Method:

In this prospective and interventional controlled study, the central corneal thickness and intraocular pressure were measured in vivo in 12 rabbit eyes treated with topical timolol maleate for 1 month and in 12 controls at baseline, and after the intraocular pressure (measured by direct cannulation of the anterior chamber) was increased to 15 and 30 mmHg using a forced saline infusion into the anterior chamber.

Results:

There were no significant differences in the basal central corneal thickness values (control group, 373.2±12.9 µm; study group, 377.5±19.2 µm, p=0.5) or the central corneal thickness values when the intraocular pressure was increased to 15 mmHg (control group, 335.2±14.3 µm; study group, 330.0±32.1 µm, p=0.6) and to 30 mmHg (study group, 318.8±25.3 µm; control group, 329.8±21.0 µm, p=0.3).

Conclusion:

Rabbit corneas treated with topical timolol maleate for 1 month did not show a strain response to acute intraocular pressure increases that differed from control eyes. This is in contrast to a previous finding in which rabbit eyes treated with prostaglandin analogues had a greater decrease in central corneal thickness in response to a sudden intraocular pressure increase compared with untreated corneas.

Effect of topical prostaglandin analogues on corneal hysteresis

PURPOSE

To evaluate possible changes in corneal hysteresis (CH) after topical treatment with a prostaglandin analogue in medication-naïve eyes.

METHODS

This was a prospective, observational cohort study. Sixty-eight eyes of 68 patients were prospectively included who were newly diagnosed with primary open-angle glaucoma or ocular hypertension in our institution. All patients were treatment-naïve. Patients were evaluated at baseline and after 6 months of treatment with latanoprost in the eye with the lower intraocular pressure (IOP) measured by Goldmann applanation tonometry (GAT). The ocular response analyzer was used to measure CH.

RESULTS

CH increased significantly (p = 0.0001) from 8.96 ± 2.3 mmHg to 9.79 ± 1.97 mmHg, and this increase was correlated significantly (p = 0.0001, r = 0.64, r(2) = 0.41) with the basal CH. We identified a weak but significant (r(2) = 0.06, p = 0.01) relationship between the basal CH and the drug-induced reduction of the GAT IOP. Nevertheless, the increase in the drug-induced CH was not correlated with the decrease in the GAT IOP.

CONCLUSION

Treatment with latanoprost increases CH. The CH increase was not correlated with the drug-induced decrease in the GAT IOP, which suggested a direct effect of latanoprost on the viscoelastic corneal properties.

A rat experimental model of glaucoma incorporating rapid-onset elevation of intraocular pressure

Glaucoma is a chronic disease that causes structural and functional damage to retinal ganglion cells (RGC). The currently employed therapeutic options are not sufficient to prevent vision loss in patients with glaucoma; therefore, there is a need to develop novel therapies, which requires the creation of functional, repeatable and easy-to-utilize animal models for use in pre-clinical studies. The currently available models ensure only low to moderate damage in optic nerves, with high variation in the outcomes and poor repeatability. We have developed an effective and reproducible rat glaucoma model based on a previous idea for a "Bead Model" in mice, which could be useful in future glaucoma research. Additionally, in an attempt to achieve rapid elevation of Intraocular Pressure (IOP), we included an initial "high-pressure injury" as part of this method, which serves as the equivalent of a severe glaucoma attack. These modifications made it possible to achieve longer lasting IOP elevation with chronic damage of retinal ganglion cells.