Welcome to Eurotimes

Fort Lauderdale — Analysis of saccadic eye movements may be a sensitive tool for early detection of thyroid-associated ophthalmopathy (TAO), according to research presented at the annual meeting of the Association for Research in Vision and Ophthalmology.

The international team of researchers recorded horizontal and vertical saccades with amplitudes of 10o, 20o, 30o and 40o in each eye of 10 normal controls; six individuals with proven autoimmune thyroid disease and no clinical evidence of TAO; and 10 patients each with early mild TAO, early severe TAO and longstanding restrictive disease.

They then analysed statistically significant differences between eyes, gaze directions and groups using the two main sequence constants Vo (describing the asymptotic maximum velocity) and (characterising the steepness of the amplitude dependent change of velocity) calculated for each eye. They were then able to reconstruct the average main sequence curves of the different groups.

Significant differences between patients and controls
There were no consistent significant differences between the controls and patients with thyroid disease in comparisons based on mean values for horizontal and vertical saccades.

However, in the analyses of behaviour at different gaze directions, the researchers noted that while the volunteers had higher saccadic velocity on downgaze versus upgaze, the opposite pattern was present among all patient groups, excluding those with mild disease. Among the latter subset of individuals, there was no difference between upgaze and downgaze velocity.

Mathematical reconstruction of the velocity curves based on calculations of the difference between the up- and downgaze saccades revealed consistent differences between the controls and each of the patient groups.

Whereas the subtraction values increased with increasing amplitude among controls, there was a decrease in all of the patient groups. Comparisons between patient groups showed the decrease was most marked in those without clinical evidence of TAO; was less pronounced in those with severe and longstanding disease; and showed the least decrease in those with mild disease.

The results of the present study demonstrate that analysis of the two main sequence constants Vo and and subsequent mathematical reconstruction of the amplitude-related velocity curves is clearly more sensitive in detecting changes of saccade dynamics than the mere evaluation of multiple saccade parameters as performed in previous studies, according to Hermann D Schworm MD, PhD, Professor of Ophthalmology and Chairman of the Department of Strabismology at the University Eye Hospital, Hamburg, Germany.

Early detection a possibility
“Not only were we able to detect changes in all stages of TAO, but as an unexpected and most fascinating finding, we also identified a pronounced change even in those patients who had no clinical signs of orbitopathy, thus pointing to the fact that the extraocular muscles must have been already affected by the disease in those individuals.

“Subsequently, with further refinement of the recording techniques, saccade analysis and construction of the main sequence curve could serve as a clinically useful routine tool for early detection and treatment of functional extraocular muscle changes due to TAO,” he said.

In the present study, the researchers employed the induction scleral search coil technique to assess saccadic movement. However, that methodology for recording eye movements is time-consuming and invasive. The technique of main sequence analysis is also very complicated.

“Perhaps in the future, this type of evaluation may be helpful in identifying which patients with thyroid disease risk developing orbitopathy. With that information, we can provide better counseling on prognosis and perhaps intervene earlier with treatment.

“Currently performed, however, the eye movement recordings require the use of anaesthetic drops and placement of a silicone probe onto the eye,” noted co-investigator Jan Ygge MD, PhD, Professor of Ophthalmology, Karolinska Institute, Stockholm, Sweden.

He said the next steps should be to evaluate the utility of an infrared-recording system that will be more acceptable to the patients and develop a method of automating the calculations for the main sequence analysis.

Top