Functional anatomy, innervation and immune regulation of the ocular surface

Purpose: The functional anatomy of the ocular surface prominently contributes to the visual function of the eye. It is aimed to describe the complexity of this system. Methods: Own results on histological, immunohistological, ultrastructural and biochemical level in the human and the rabbit eye are discussed together with results from the literature. Results: The ocular surface in a functional view consists of the mucosal surfaces of the globe and lid (cornea & conjunctiva) and of its mucosal adnexa (lacrimal gland & lacrimal drainage system) and it also includes the lid apparatus required for eye closure and blinking in order to provide lubrication. Different functional systems interact to produce the intact functional anatomy. These are e.g. epithelial differentiation, secretion, lid motion and immune defence that together lead to the higher order function of wetting and comfort. Ultimately they allow the preservation of corneal clarity and visual function at the ocular surface level. These systems are governed by similar underlying regulatory mechanisms as e.g. growth factors, cytokines, hormones, neuromodulatory molecules and innervation which are all shown to be involved in ocular surface function and also interact through common signalling molecules. An important functional system is the immunological defence system of the ocular surface that is known as the Eye-Associated Lymphoid Tissue (EALT) and appears to have a central integrative role. Conclusions: Different functional systems interact at the ocular surface by interactions based on common signalling molecules, which may also allow psycho-neuro-immunological regulation. An integrative understanding of the physiological state may also give insight into potential interventions under pathologic conditions.