Some new aspects of the nerve supply of the cornea and conjunctiva

The TFOS International Workshop on Contact Lens Discomfort: report of the subcommittee on neurobiology

This report characterizes the neurobiology of the ocular surface and highlights relevant mechanisms that may underpin contact lens-related discomfort. While there is limited evidence for the mechanisms involved in contact lens-related discomfort, neurobiological mechanisms in dry eye disease, the inflammatory pathway, the effect of hyperosmolarity on ocular surface nociceptors, and subsequent sensory processing of ocular pain and discomfort have been at least partly elucidated and are presented herein to provide insight in this new arena. The stimulus to the ocular surface from a contact lens is likely to be complex and multifactorial, including components of osmolarity, solution effects, desiccation, thermal effects, inflammation, friction, and mechanical stimulation. Sensory input will arise from stimulation of the lid margin, palpebral and bulbar conjunctiva, and the cornea.

Corneal sensitivity in patients with leprosy and in controls

AIMS

In a quantitative prospective study the corneal sensation in patients with leprosy was compared with age matched controls.

METHODS

The patients with leprosy were classified as paucibacillary and multibacillary and were divided in three groups: (1) patients without clinically detectable eye pathology; (2) patients with lagophthalmos, (3) patients with signs of iridocyclitis. The corneal sensitivity was assessed with the Cochet and Bonnet aesthesiometer.

RESULTS

There was a significant decrease in corneal sensitivity in multibacillary patients without clinically detectable eye pathology and in patients with lagophthalmos or iritis when compared with controls. A significant correlation between the loss of power of the orbicularis oculi muscle and the degree of corneal sensation loss could not be established. No significant decrease in corneal sensitivity was found in paucibacillary patients without eye pathology compared with the control group.

CONCLUSION

The results of this study showed that loss of corneal sensation can occur while there is no clinically detectable eye pathology, at least in multibacillary patients. Regular checkups of the corneal sensation should, therefore, be part of the routine control of leprosy patients. Health education on eye care and early warning signs should be encouraged.

The source of sensory fibres of the inferior conjunctiva of monkeys

Dissection, light and electron microscopy combined with degeneration induced by intracranial nerve lesions and superficial nerve transection were used to trace the sources of sensory fibres of the inferior conjunctiva of cynomolgus monkeys. Most nerves destined for the inferior conjunctiva were branches of the lacrimal nerve and entered the inferior eyelid laterally. Following unilateral ophthalmic neurotomy in three monkeys and combined ophthalmic/maxillary neurotomy in one monkey, substantial and regular degenerative changes were observed in the nerves and nerve-fibre bundles of the inferior conjunctiva. Following intracranial lesions of the maxillary nerve and of the infra-orbital nerve at its facial hiatus, conjunctival nerves showing induced changes were infrequent (four animals) or absent animal). The results indicate that the inferior conjunctiva is innervated mainly by the ophthalmic nerve contrary to the popular notion that it is innervated mainly or wholly by the infra-orbital branch of the maxillary nerve.