City Research Online

Abstract

This study sought to investigate the structure, distribution, and functional significance of complex (corpuscular) nerve endings in the conjunctiva of the human eye. Although these were found to be widely distributed throughout the conjunctiva they were particularly common at the corneo- conjunctival junction and at the eyelid margin.

Corpuscular nerve endings were round or oval encapsulated structures which varied in size (mean greatest diameter 40/xm, range 20-78/xm). Each corpuscle was generally served by a single myelinated nerve fibre. The myelin sheath was lost soon after entering the body of the structure. The terminal axon was characterised by multiple beads or varicosities which contained an accumulation of mitochondria. Neural elements were surrounded by cytoplasmic processes of Schwann like cells. The capsule was variable in thickness and typically consisted of fibrocyte processes. In contrast, some corpuscles at the eyelid margin displayed a capsule which contained perineural cells.

An intra-vital staining technique using methylene blue was used on the living conjunctiva (N=6). Compared with histological technique this method appears to considerably underestimate the number of complex nerve endings.

In an attempt to correlate the position of sensory corpuscles with points of enhanced touch sensitivity an investigation of the sensitivity of the limbal conjunctiva was carried out using a Cochet-Bonnet aesthesiometer. Subjects consisted of both non-contact lens wearers (N=28) and contact lens wearers (N=22) (Hydrogel N=10, RGP N=12). Limbal touch thresholds (LTT) were determined at 18 test locations which were divided equally between the temporal and inferior limbus. Regional variations in LTT were apparent. Thresholds increased with increasing distance from the cornea. Sensitivity was greatest in the region of the conjunctiva corresponding to the palisade zone. This was found histologically to contain a greater concentration of putative receptors. Large inter-subject variations in sensitivity were recorded, and there was an overall reduction with age. A comparison of LTT between lens wearers and non-wearers failed to show any significant differences.

The variations in LTT apparent in this study may correlate with the variations in the incidence and local distribution of sensory corpuscles.

Publication Type:	Thesis (Doctoral)
Subjects:	R Medicine > RZ Other systems of medicine
Departments:	School of Health & Psychological Sciences > Optometry & Visual Sciences School of Health & Psychological Sciences > School of Health & Psychological Sciences Doctoral Theses Doctoral Theses

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