Saccadic eye movement measurements in the normal eye: Investigating the clinical value of a non-invasive eye movement monitoring apparatus.

Abstract

Clinicians are becoming increasingly aware of the effect of various pathologieso n the characteristicso f saccadice ye movements.A s such, an efficient and non-invasivem eano f measuringe ye-movementisn a clinical environmenti s of interest to many. The aim of this thesis is to investigate the clinical application of a non-invasive eye movement recording technique as a part of a clinical examination. Eye movements were measured using an IRIS 6500 infrared limbal eye tracker, which we customized for the direct recording of oblique eye movements as well as horizontal and vertical. Firstly, the eye-tracker itself was assessed. Visually normal observers made saccadic eye movements to a 10' stimulus in eight directions of gaze. Primary (ANOVA) and secondary analyses (mean error less than 5%) resulted in acceptance that averaging four measurements would give a representative measurement of saccadic latency, peak velocity, amplitude and duration. Test-retest results indicated that this technique gives statistically (± 1.96*STDEVDifference) repeatable responses. Severalf actors that could potentially influence clinically basedm easureso f eye-movementsw ere examined. These included, the effect of ageing, viewing distances, dioptric blur and cataract. The results showed that saccadic latency and durationa re significantly (p< 0.05) longer in older (60-89 years)o bserversc ompared to younger (20-39 years). Peak velocity and amplitude were not significantly affectedb y the age of the observer.A ll saccadicp arameters( SP) were significantly affected by direction (Chapter 5). The compact nature of this eye movement methodology is obtainable since there is no significant effect on viewing distance (300 cm vs. 49 cm) (Chapter 6). There is also no significant effect of dioptric blur (up to +LOODS) on any of the four SP. In contrast, a higher level of defocus (+3.O ODS)h as a larger probability of interfering with the measurementso f peak velocity and duration (Chapter 7). Saccadice ye-movementsw ere also recorded whilst normally sighted subjects wore cataract simulation goggles. The results suggested that the presence of dense cataract introduces significant increases in saccadic latencies and durations. No effect was found on the peak velocities and amplitudes.T he effect of amblyopiao n SP was also investigatedin order to examine if this methodologyi s able to detectn ormal from abnormalr esponses(i . e. increased saccadicla tencies).T his set of data (Chapter9 ) showedt hat using IRIS 6500, longer than normal latencies may be recorded from the amblyopic eye but no consistent effect was found for the other SP (peak velocity, amplitude, duration). overall, the results of this thesis demonstrateth at the IRIS 6500 eye-tracker has many desirable elements (it is non-invasive; comfortable for the observers and gives repeatable and precise results in an acceptable time) that would potentially make it a useful clinical tool as a part of a routine examination.