Effect of selective topical anaesthesia on the initial comfort of rigid contact lenses

The primary sensory location of contact lens discomfort remains unclear. This study utilised selective topical anaesthesia of the ocular surface to investigate if the relative contribution of different tissues to lens-related discomfort could be determined.

This was a randomised, subject-masked, contralateral eye pilot study involving 10 participants. Mechanical sensitivity was measured at three locations on the ocular surface (cornea, upper and lower eyelid marginal conjunctiva) using a Cochet-Bonnet aesthesiometer. Following sensitivity measurements, proxymetacaine hydrochloride 0.5% was topically applied to one of the three locations in one eye whilst 0.9% saline was applied to the corresponding location in the fellow eye as a placebo. Sensitivity measurements were then repeated. A pair of rigid contact lenses was subsequently applied and comfort scores were recorded after 5 min using a 0-100 visual analogue scale.

The sensitivity of the location anesthetised decreased significantly (all Bonferroni-adjusted p<0.006), whilst the sensitivity of the unanaesthetised remaining two locations showed no significant change (all p>0.05). There was no significant change in sensitivity following the application of saline (all p>0.05). There was no significant difference in comfort following lens application between the anaesthetic and saline for the cornea and lower lid marginal conjunctiva [LSM difference (95% CI): -3.0 (-11.3, 5.3) and 2.0 (-6.3, 10.3), respectively]. However, comfort was significantly better when the upper lid marginal conjunctiva was anaesthetised compared to saline application [12.3 (4.0, 20.6)].

This work has demonstrated a novel technique which can successfully selectively anaesthetise specific regions of the ocular surface. The initial comfort of rigid lenses was better when the upper lid marginal conjunctiva was anaesthetised, which supports the hypothesis that initial comfort of rigid lenses may be driven by the interaction between the lens and the upper eyelid. This work may also have significant utility for investigating discomfort in soft contact lenses.