Central Connections of the Lacrimal Functional Unit

Abstract

2 ABSTRACTPurpose 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.3

Tear Metabolomics in Dry Eye Disease: A Review

“…Continuous secretion of tears is stimulated parasympathetically through the nervus intermedius of the nervus facialis, leading to reflectory blinking (approximately 12 blinks per min) with even physiological moistening of the ocular surface in the absence of any irritation. The dysfunction of any component of the lacrimal functional unit can alter the quality or quantity of tears, resulting in DED [46,47,48,49,50,51,52].…”

Regeneration of Lacrimal Gland Function to Maintain the Health of the Ocular Surface

“…Tears are secreted by the lacrimal functional unit, which is composed of the ocular surface, the main and accessory LGs, lacrimal puncta, and the neural network connecting them; notably, this functional unit is extremely complicated. [33][34][35] The LG complex system maintains the health of the ocular surface tissues, and reflexively regulates aqueous tear homeostasis (Fig. 1).…”

Effects of ambient humidity on the Cochet–Bonnet aesthesiometer

“…The primary role of the corneal innervation is to detect foreign bodies and noxious substances that come in contact with the eye. The dense neural network at the corneal surface provides a high level of sensitivity that also plays a primary role in the regulation of basal tears via the lacrimal function unit [1,2]. The assessment of corneal sensitivity can provide an indication of neural functioning, which, when compromised, can lead to disruptions in the trophic maintenance and repair of the corneal epithelium [3,4].…”