Abstract
BackgroundIntraocular pressure (IOP) is an important physiological measure of the eye and is associated with some ocular disorders. We aimed to assess the influence of topical beta blocker-induced IOP reduction on lens-induced axial elongation in young guinea pigs.MethodsThe experimental study included 20 pigmented guinea pigs (age: 2–3 weeks). Myopia was induced in the right eyes for 5 weeks with − 10 diopter lenses. The right eyes additionally received either one drop of carteolol 2% (study group, n = 10) or one drop of artificial tears daily (control group, n = 10), while the contralateral eyes of all animals remained untouched. The outcome parameter was axial elongation during the follow-up period. The mean of all IOP measurements taken during the study was referred to as mean IOP.ResultsGreater axial elongation was associated with a shorter axial length at baseline (P < 0.001; standardized regression coefficient beta: − 0.54) and lens-induced myopization (P < 0.001; beta: 0.55). In the multivariable model, axial elongation was not significantly correlated with the IOP at study end (P = 0.59), the mean IOP during the study period (P = 0.12), the mean of all IOP measurements (P = 0.17), the difference between the IOP at study end and baseline IOP (P = 0.38), the difference between the mean IOP during the study period and the baseline IOP (P = 0.11), or the application of carteolol eye drops versus artificial tears eye drops (P = 0.07). The univariate analysis of the relationships between axial elongation and the IOP parameters yielded similar results. The inter-eye difference between the right eye and the left eye in axial elongation was significantly associated with the inter-eye difference in baseline axial length (P = 0.001; beta:-0.67) but not significantly correlated with the inter-eye difference in any of the IOP-related parameters (all P > 0.25).ConclusionsIn young guinea pigs with or without lens-induced axial elongation, neither the physiological IOP nor the IOP reduced by carteolol, a topical beta-blocker, was associated with the magnitude of axial elongation. These results suggest that IOP, regardless of whether it is influenced by carteolol, does not play a major role in axial elongation in young guinea pigs.
Highlights
Intraocular pressure (IOP) is an important physiological measure of the eye and is associated with some ocular disorders
Based on observations made in eyes with congenital glaucoma and in adult hypotonic phthisic eyes, the possibility that the IOP may play a role in primary axial myopia has been discussed, and it has been debated whether IOP in the upper normal range contributes to the expansion and elongation of the globe [8,9,10,11,12]
The axial length was significantly shorter in the right eyes of the study group than in the right eyes of the control group (8.61 ± 0.12 mm versus 8.70 ± 0.06 mm; P = 0.038)
Summary
Intraocular pressure (IOP) is an important physiological measure of the eye and is associated with some ocular disorders. Based on observations made in eyes with congenital glaucoma and in adult hypotonic phthisic eyes, the possibility that the IOP may play a role in primary axial myopia has been discussed, and it has been debated whether IOP in the upper normal range contributes to the expansion and elongation of the globe [8,9,10,11,12]. The hypothesis is supported by findings reported in some populationbased studies In these investigations, a higher IOP was associated with a longer axial length and higher myopic refractive errors after the statistical model was adjusted for parameters influencing IOP [13, 14]. Other studies reported contradictory results: in the population-based investigations of the Central India Eye and Medical Study and the Beijing Eye Study, axial length was not significantly related to IOP [18, 19]
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