In a pilot study the effect of bilateral inferior punctal occlusion on the ocular hypotensive effect was evaluated after topically applied timolol using silicone punctal plugs. A randomized, double-masked, cross-over clinical trial was conducted, comparing the ocular hypotensive effect of timolol maleate 0.25 percent, both with and without occlusion of the inferior punctum with the Freeman silicone punctal plug. Following a 2-week washout of topical medication, 17 subjects with early primary open-angle glaucoma or ocular hypertension received one drop of timolol 0.25 percent in each eye with or without punctal plugs in place. Blood pressure, resting pulse rate, and intraocular pressure were measured both before timolol instillation and at intervals of 1, 2, 4, 8, and 12 hours following drop instillation. Following a 2-week washout period, the subjects were evaluated with the alternative treatment. There was no statistically significant difference (p = 0.648) in IOP levels between treatment groups «Bartlett JD, Boan K, Corliss D ym. Efficacy of sil...»1.
In another study twenty patients with primary open angle glaucoma who have been treated with identical antiglaucoma eye drops in both eyes were examined. Silicone punctal plugs were used to occlude the inferior punctum of one eye, in order to block the nasolacrimal canal. The intraocular pressures and effects of the medical therapy before and after punctal occlusion were compared. Punctal occlusion significantly decreased the intraocular pressure with an average of 2.00 +/- 0.43 mmHg in the plugged eyes (p< 0.001). The intraocular pressure in the unplugged control eyes did not change significantly (p> 0.05) after punctal occlusion of the fellow treated eye «Aritürk N, Oge I, Erkan D ym. The effects of nasol...»2.
In a study silicone punctal plugs were used to occlude the inferior punctum of one eye in each of 19 patients treated with identical antiglaucoma eyedrops in both eyes. The intraocular pressures before and after punctal occlusion were compared. The eyes with the punctal plugs showed a statistically significant (p<0.0001) decrease in pressure of 1.32 mm Hg after punctal occlusion when compared to that of the fellow control unplugged eyes. The intraocular pressures in the plugged eyes decreased an average of 1.82 mm Hg after punctal occlusion when compared to before punctal occlusion (p = .001) «Huang TC, Lee DA. Punctal occlusion and topical me...»3.
The effect of temporary punctal occlusion is studied also in normal subjects and the conclusion was: Temporary punctal occlusion in normal subjects decreases tear production and ocular surface sensation. The findings suggest that in addition to blocking tear drainage, punctal occlusion may affect the ocular surface/lacrimal gland interaction. These effects were more pronounced in subjects with both upper and lower puncta occluded «Yen MT, Pflugfelder SC, Feuer WJ. The effect of pu...»4.
In Finnish studies there has been shown that temporary occlusion of nasolacrimal puncta decreases the systemic absorption of the glaucoma medication «Salminen L. Review: systemic absorption of topical...»6, «Kaila T, Huupponen R, Salminen L. Effects of eyeli...»7, «Urtti A, Salminen L. Minimizing systemic absorptio...»8, «Zimmerman TJ, Sharir M, Nardin GF ym. Therapeutic ...»9.
There was also described artificial occlusion of lacrimal puncta by serious cicatrizing conjunctivitis caused by glaucoma medication «McNab AA. Lacrimal canalicular obstruction associa...»5.
Comment: Nasolacrimal compression has beneficial effects in glaucoma therapy and should be learned to every new glaucoma patient at the beginning of the therapy. Further, every new glaucoma patient needs instructions how to drop in the eye. In policlinics this instruction could be given by ophthalmic nurses and in private practice by nurse or by the ophthalmologist itself. In general this important instruction is neglected in many places. It is important to keep mind that "how to drop" is not clear for many patients.