|Year : 1985 | Volume
| Issue : 1 | Page : 41-43
Pupil cycle time
AK Sood, Sandeep Mithal, Arun Elhence, Anil Maini
Deptt. of Ophthalmology, L.L.R.M. Medical College, Meerut, India
A K Sood
Department of Ophthalmology, L.L.R.M. Medical College, Meerut
Source of Support: None, Conflict of Interest: None
|How to cite this article:|
Sood A K, Mithal S, Elhence A, Maini A. Pupil cycle time. Indian J Ophthalmol 1985;33:41-3
Pupil cycle time is a simple and reliable clinical test to diagnose defects in the pupillary pathways. It is a measure of the relative conduction speed of the afferent and efferent pupillary pathways. Apart from neurological conduction defects several non-neurological defects can slow down pupillary cycle time and thus hinder proper estimation of the conduction speed. The aim of the present study is to find out whether such variables as age and sex, refractive error, and iris colour significantly aeter pupil cycle time in otherwise neurologically normal persons.
| Material and methods|| |
The present study was conducted on 112 eyes of 56 normal persons. Prior to inclusion in this study the patients were screened for any neurological deficit, ocular mobility disorders, gross field defects, retinopathies and macular disorders. Visual acuity was normal with correction in all members of the study group. 50% of the groups were males and the remaining females.
Pupil cycle time was measured in both eyes using a Haagstreit type slit lamp and 1/100th sec. band held stop watch. Intensity of illumination was kept fixed for the entire study. The patient is comfortably seated at the slit lamp in a dimly lit room. He removes his spectacles if he wears one. A horizontal slit beam of light about t mm thick is focussed on to the iris at the inferior limbus. The beam is then elevated until it just overlaps the inferior margin of the pupil which then contracts and prevents light from entering the pupil. The retina is now in darkness and the pupil dilates to overlap the edge of the light beam again, producing another pupillary constriction, thus setting up persistent oscillations. 25 such cycles are timed in two separate runs and the average time for each cycle calculated.
| Observasions|| |
The average pupil cycle time in males was 928.4 ms and in females 934.0 ms. The average pupil cycle time for the entire group of 56 persons (112 eyes) was 931.2 ms.
The pupil cycle time for each of the different age groups is given in [Table - 1]. The pupil cycle time among the older age group (56-65 years) was higher than in the proceeding group.
Among the emmetropic eyes the average pupil cycle time was 928.4 ms. Among hypermetropes it was 927.8 ms and among myopes it was 936.7 ms [Table - 3].
The minimum difference in pupil cycle time between the two eyes was 32 ms and the maximum difference 98 ms. The mean difference between the two eyes being 1 5 ms. Among right eyes the pupil cycle time was 928.9 ms and left eyes it was 933.6 ms [Table - 2].
Pupil cycle time in eyes with dark irides was 932.0 ms and in light irides 929.8 ms.
| Discussion|| |
Oscillations are a common and important instance of the mal-functioning of a servomechanism. Oscillations are also a common pathological abnormality in a wide variety of neurological diseases and are manifest in such clinical signs as tremors, ataxia, clonus and nystagmus.
Hippus is usually considered to be either pathologic or a physiologic variant of the normal pupillary unrest. It has been compared to a physiologic tremor. Hippus generally is regarded as of little or no diagnostic value because it has been seen in normal persons. However, it has been reported in a wide variety of conditions including Neurosyphilis, brain tumor, epilepsy, multiple sclerosis, congenital chorea, posterior fossa lesions, Schizophrenia, barbiturate and paraldehyde poisoning, meningitis and coma. Pupil cycle time is also significantly longer in patients with optic neuritis and compressive optic neuropathy.
In our present study although there is a difference of about 6 ms between males and females, it is not statistically significant.
Similarly there is no statistically significant difference between Pupil cycle time of age group between 15 to 55 years. Miller and Thompson have mentioned a significant but small (+2.4 ms/year) trend of increasing cycle time with age. However, the pupil cycle time of the 56 to 65 years age group is significantly prolonged in comparison to younger age groups 5. It seems thus that pupil cycle time is prolonged with age but there is no steady demonstrable increase in pupil cycle time with age as shown by Miller and Thompson.
Myopes in this study had longer pupil cycle time than hypermetropes and emmetropes but this difference is not statistically significant. Miller and Thompson 5 have also mentioned that pupil cycle time was not significantly affected by refractive error. In all the cases the pupil cycle time in the two eyes was found to be different. The mean difference being about 15 ms. Probably each pupillary pathways has its own inherent conduction speed which remains stable under testing conditions.
Average pupil cycle time in eyes with dark irides was slightly longer than in eyes with light coloured irides but again there was no statistically significant difference.
Pupil cycle time can thus be used as a fast, simple and reliable clinical test of optic nerve functions. It is probably not as reliable as the VER and the pupillary afferent defect estimations but has the advantage of being extremely easy to carry out.
| Summary|| |
The pupil cycle time appears to be quite a stable entity, not showing any statistical differences among eyes of males and females, different refractive status, and different coloured irides. Each eye appears to have its own steady rate of cycling accounting for the difference in pupil cycle time in two eyes of the same normal individual. Advancing age does appear to prolong the pupil cycle time but this could be explained by increasing incidence of senile miosis as age advances.
| References|| |
Yoss, R.E., Moyer, N.J., Hippus and Hollen Harst, R.W., 1970, Amer. J. Ophthalmol , 70: 935.
Miller. S.D. and Thompson, H.S.. 1978, Amer. J. Ophthalmol., 85: 635.
Thompson H.S., 1981, Adler's physiology of the eye p. 340.
Miller, and Thompson 1978 : Brit. J. Ophthaimol., 62: 495.
[Table - 1], [Table - 2], [Table - 3]