Abstract
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.
Highlights
Glaucoma, the second leading cause of visual loss wordwide [1], is an acquired optic neuropathy with progressive retinal ganglion cellular death that leads to irreversible visual field loss [2].1874-3641/18 2018 Bentham OpenAcute Increases in Intraocular PressureThe Open Ophthalmology Journal, 2018, Volume 12 315Increased Intraocular Pressure (IOP) is one of the most important risk factors for glaucoma development, and the only effective treatment is lowering of the IOP
To further investigate if these biomechanical effects are related to the IOPlowering effect of PGs or result from the direct effect of these drugs on the corneal collagen structure, we evaluated the effect of treatment with other topical antiglaucoma drugs, such as timolol maleate, on the corneal response to acute IOP increases in rabbit eyes
Five minutes after the anterior chamber pressure was stabilized at 15 mmHg, the Central Corneal Thickness (CCT) values decreased in both groups; the mean CCT decreased to 335.2 ± 14.3 and 330.0 ± 32.1 μm in the control and study eyes, respectively (p=0.002 for both comparisons)
Summary
Increased Intraocular Pressure (IOP) is one of the most important risk factors for glaucoma development, and the only effective treatment is lowering of the IOP. The accuracy of the IOP measurement is of paramount importance. Goldmann Applanation Tonometry (GAT) is the current gold standard for IOP measurement [3]. It is well known that some corneal characteristics, such as the Central Corneal Thickness (CCT), clearly affect the accuracy of the GAT IOP measurements [4]. Corneal biomechanical properties, such as Young’s modulus of elasticity, might have a greater impact on IOP measurements than the CCT [5]. The posterior corneal surface is more elevated in patients with glaucoma than in healthy subjects [6], lowering the IOP in steroid-induced glaucoma decreases the posterior corneal elevation and the CCT [7] and IOP elevation produces refractive changes in patients who underwent a previous corneal laser refractive surgery [8]
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