Central connections of the lacrimal functional unit

Purpose To study the contribution of each eye to the reflex tear response, after unilateral and bilateral topical anaesthesia. Method A closed eye, modified Schirmer test was performed bilaterally in 8 normal subjects, in a controlled environment chamber set to 23°C, 45% relative humidity and 0.08m/s airflow. Eye drops were instilled into each eye 10 minutes before the Schirmer test. Experiments were: a) bilateral saline (control) b) unilateral anaesthesia (ipsilateral anaesthetic; contralateral saline) and c) bilateral anaesthesia. Results There was no difference in between-eye wetting lengths in the saline control eyes (p = 0.394) or the bilaterally anaesthetised eyes (p = 0.171). Wetting length was reduced in both eyes after bilateral anaesthesia compared to saline controls (p = 0.001; p = <0.0005). After unilateral anaesthesia, wetting length was reduced in the anaesthetised eye compared to its saline control by 51.4% (p = <0.0005) and compared to its fellow, unanaesthetised eye (p = 0.005). The fellow eye value was also reduced compared to its saline control (p = 0.06). Conclusions Wetting length was reduced by topical anaesthesia, when instilled bilaterally and ipsilaterally. The latter response implies an ipsilateral, reflex sensory drive to lacrimal secretion. In the unanaesthetised fellow eye the reduction compared to its saline control was not quite significant. This implies a relative lack of central, sensory, reflex cross-innervation, although the possibility cannot entirely be ruled out. These results are relevant to the possibility of reflex lacrimal compensation from a normal, fellow eye, in cases of unilateral corneal anaesthesia.