We obtained informed consent from each participant, and our study was approved by the Institutional Review Board. The study was comprised of 30 eyes from 30 healthy volunteers (18 male, 12 female). One eye of each patient was selected randomly for the analysis. The average age of the subjects was 27.4 years (26 - 32). The criteria for this study required a completely normal ophthalmic examination after pupil dilation with a best-corrected vision ≥ 20/25, IOP < 20 mmHg and no family history of glaucoma. IOP was measured in all patients before the goggles were applied, at 5, 10, 30 and 60 minutes after the goggles were put on, and then immediately after the goggles were removed. Blood flow of the ONH was measured immediately before and after the goggles were worn. As shown in Fig. 1, the lenses of the goggles were removed to allow the measurement of the IOP. The IOP was measured at each time-point by one examiner (CWS) three times, and the readings were averaged. A Heidelberg retinal flowmeter (HRF) (Heidelberg Engineering GmbH, Heidelberg, Germany) was used to measure the blood flow of the ONH. One examiner measured all the patients, and then the data was analyzed using an Automatic Full-Field Perfusion Image Analyzer (AFFPIA) program, which calculated the 'average flow'.2,3 Arbitrary units (AU) were used in the HRF software to measure blood flow, volume and velocity measurements. The conventional method to measure blood flow in the ONH, which uses a sampling technique in a 10 × 10 pixel frame, can show a fluctuation according to the selection of the pixels. In this case to analyze the blood flow, the AFFPIA uses two circles with one just inside the margin of the optic disc and the other just outside the optic pit, ensuring precision in the measurements.

The difference between IOP before and after wearing swimming goggles was analyzed using repeated measurements and Analysis of Variance(ANOVA) with Bonferroni correction. The statistical significance was set at p < 0.05.

The IOP before the swimming goggles were worn was 11.88 ± 2.82 mmHg (mean ± SD; n=30). The IOP increased by 2.32 mmHg (p < 0.05) to 14.20 ± 2.82 mmHg (mean ± SD; n=30) immediately after the goggles were put on. Over the 60 minutes while the goggles were worn, the average IOP was 14.63 ± 2.92 mmHg (mean ± SD; n=30) at five minutes, 14.72 ± 2.94 mmHg (mean ± SD; n=30) at 10 minutes, 14.60 ± 2.78 mmHg (mean ± SD; n=30) at 30 minutes and 14.51 ± 2.82 mmHg (mean ± SD; n=30) at 60 minutes (p < 0.05). The IOP decreased to 11.78 ± 2.89 mmHg (mean ± SD; n=30) immediately after the goggles were taken off(Fig. 2). The HRF showed an average flow of 336.60 ± 89.07 AU (mean ± SD; n=30) before the goggles were put on, and decreased to 319.18 ± 96.02 AU (mean ± SD; n=30) immediately after they were taken off. However, the difference between these two values did not show statistical significance (p =0.58).

Various activities in everyday life have been reported to increase intraocular pressure. Playing the trumpet has been reported to elevate the IOP by 20 mmHg,4 the Sirsasana posture in yoga has been shown to induce IOP to rise up to 15.8 mmHg,5 and the necktie has been shown to be responsible for a 1.58 mmHg rise in IOP.6,7 In this study, swimming goggles resulted in a 2.4 mmHg increase in IOP. This rise may not be as high as that of musicians playing the trumpet or yoga practitioners in the Sirsasana posture, but it is greater than the IOP rise caused by neckties. Although this increase in IOP may not have a significant effect on normal participants, any elevation of IOP, such as that caused by the wearing of swimming goggles, may be detrimental to patients with advanced glaucoma.8 The IOP elevation was observed immediately after the goggles were put on, and this elevation returned to a normal level immediately after they were removed. Although the decrease in IOP immediately after removing the goggles did not have statistical significance, it does imply that the change in IOP is a result of direct pressure on the periorbital tissue.

This preliminary study has been performed in normal subjects who are much younger than the average glaucoma patient, so further studies in glaucomatous subjects are necessary. Also, this study simulates only partial effects of the swimming goggles because the anterior section of the lens was removed. The vacuum pressure inside the chamber formed in each eye by the goggles should also be considered.

This study used one common type of swimming goggles, and so a different goggle design which has less pressure around periorbital tissue could have a different effect on IOP. Therefore, advanced glaucoma patients who use swimming goggles regularly should be carefully monitored, or should use specially-designed swimming goggles that produce minimal pressure around the eyelid.