FP1292 : Measuring Eye Motility Reliably: Ocular Motility Tester.
Dr.Jitendra Nenumal Jethani, J09433, Mr.Rutvij Kotecha
Abstract
Ocular motility is a study of 12 extraocular muscles and how they impact eye movement. It is very important for a neuroophthalmological examination to know the excursion of the eye in a patient. Currently it is measured byKestenbaum’s ruler, Urist lateral reflex test, and projecting the image on Hess screen. We present a refined ocular motility tester. It consists of two visual display units (VDU), two cameras, and a computing device. The patient will turn the eyes in the direction instructed on VDU, the camera will record the motion, and software on the computing device will perform image processing to compute the movement in millimeter. The device was tested on 20 normal subjects with mean age 20.4 +/- 1.2 years. The mean adduction was 9.18 +/- 1.5, mean abduction 8.9 +/- 1.6, mean elevation 8.1 +/- 1.1 and mean depression was 9.1 +/- 1.4 mm. Ocular motility tester can tell us the normal excursions, help us in underactions of muscles in neuro-ophthalmological problems and recovery.
Ocular motility examination is a part of standard eye examination. The amount of eye excursion is important to decide whether a particular eye movement is normal or not. The normal values for this needs to be found. Some earlier studies done by Kestebaum and Urist are available1-3 but the common practice is to measure it like a grading system of -4 where there is no movement of eye and -5 where the eye doesn’t even come to the midline and 0 is normal and +1 shows an exaggerated or an overaction of the muscles. We designed a small setup which can be used to reliably measure the ocular excursion
Materials and Methods
It consists of visual display units (VDU), cameras, and a computing device. The patient will turn the eyes in the direction instructed on VDU. The camera will record the motion and software on the computing device will perform image processing to compute the movement in millimeters.
The device can be mounted on a slitlamp and the target can be moved on each side. The device would capture the centre of the eye and the limbus and then the extreme movements would be taken as still. The device would also try to calculate the speed of the movement of the eye. Once the pictures are taken the device via its computing software would measure the amount of movement and excursion and would give a reading in millimetres.
The device was tested on 20 normal subjects with mean age 20.4 +/- 1.2 years. All subjects were normal with no refractive error and no ocular motility problem.
Results
The device was tested on 20 normal subjects with mean age 20.4 +/- 1.2 years. The mean adduction was 9.18 +/- 1.5, mean abduction 8.9 +/- 1.6, mean elevation 8.1 +/- 1.1 and mean depression was 9.1 +/- 1.4 mm. This was mainly to establish the normative data.
The device was tested by two independent observers masked to each others’ findings. We found a good agreement (p= 0.91) between the two observers using the device.
Discussion
Various methods have been used in the past to measure the ocular motility.1Kestenbaum’s technique used a ruler tomeasure the ocular motility.2 He established the normal motility at 9-10 mm for adduction, abduction and depression and the elevation movement was 7 mm. A similar probably simpler method was also devised by Urist et al. 3 This was called lateral light reflex test. Each mm displacement from the centre was around 7mm. The test was obviously having a limitation that the examiner has to estimate the centration of the light and then the amount of movement in terms of degrees.1
Another novel method was proposed by Kushner et al 4, here he prosposed to use a cervical range of ocular motility tester mainly used for orthopaedic surgeon to assess the joint motility. Here, the movement of eyes is measured by asking the patient to fix on the target and movement of head. He found it to be fairly accurate.
Holmes et al 5 devised a photographic method similar to ours. He found a good interobserver correlation. Photographs were taken when thepatient looked to right and left gaze positions. Using a
ruler the examiner measured the deficit of abduction inmillimetres. The repeatability of the method wasevaluated using a standard grading system for documentingand grading abduction deficit.
Our device is similar to Holmes et al except that the measurements would be taken directly by the computer algorithm and this would make it less time consuming and more repeatable. A non-technical person may also be able to use the device.
Conclusion
A new device to accurately measure the ocular excursions has been tested. The measurements are reliable between the observers.
Future research
The device has been made also to record the ocular motility. This may help in finding out the saccadic speed and the lag if at all. We may be able to differentiate the type of underaction depending on the speed of ocular motility.
References
- Hanif S, Rowe F, O’connor A. A comparative review of methods to record ocular rotations Br IrOrthopt J 2009; 6: 47–51
- Kestenbaum A. Clinical Methods of Neuro-ophthalmological Examinations, 2nd edition. New York and London: Grune& Stratton, 1961.
- Urist MJ. A lateral version light reflex-test. Am J Ophthalmol1967; 63: 808–815.
- Kushner BJ. The usefulness of the cervical range of motion device in the ocular motility examination. Arch Ophthalmol2000; 18: 946–950.
- Holmes JM, Hohberger GG, Leske DA. Photographic and clinical techniques for the outcome assessment in sixth nerve palsy.Ophthalmology2001; 108: 1300–1307.
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