Tear Film Thickness and its Effects on the Recording of Multi-electrode Electroretinographic Responses

Glaucoma is a progressive neurodegenerative disorder in which ocular stressors adversely affect retinal ganglion cells, causing dendritic and axonal atrophies that eventually lead to cell death and irreversible loss of vision. It is estimated that by the year 2020 the disease will affect more than 80 million individuals worldwide. Thus the effective management of glaucoma represents a critical, unmet medical need. Toward this end, the irreversible nature of glaucomatous vision loss dictates that the disease must be detected early in its progression if the efficacy of treatment plans is to be maximized. However, the early detection of glaucoma remains a difficult task. To overcome this challenge, the novel technology behind multi-electrode electroretinography has been developed by Dr. John Hetling of the University of Illinois at Chicago. This novel approach to elecroretinography uses a Contact Lens Electrode Array (CLEAr Lens™) to record spatially distinct bioelectric potentials from the cornea. These biopotentials are then used to interpret the health of the retina. It is hypothesized and supported by early data that via this approach, spatially localized functional deficits, such as those associated with glaucoma, can be detected at early stages of disease progression. The technique of multi-electrode electroretinography is dependent upon the recorded corneal potentials being spatially distinct. That is, the signals must preserve unique information about the underlying source currents generated by retinal activity. However, such information is lost if the signals are shunted together, which may occur if tear film between the cornea and recording lens is too thick. This places particular importance upon the thickness of this tear film with respect to the multi-electrode electroretinogram (meERG) project. Thus, this Thesis will be focused upon studying the dynamics of the tear film thickness beneath the CLEAr Lens. Through measuring tear film thickness in the ~20 minutes that follow lens insertion, we seek to investigate how tear film thickness affects meERG recording. We hypothesize that following lens insertion, there is a lens-settling period over which tear film thickness changes. Furthermore, we hypothesize that these changes in tear film thickness will induce predictable alterations in meERG responses. To examine these hypotheses, the current study seeks to determine how tear film thickness changes over the course of the lens settling period, and how these changes are manifested in meERG responses.