![]() ![]() In part this may be due to the variation in resting pupil size, since a smaller pupil admits less of the stimulus under closed-loop conditions an autonomic control system whereby a mechanism is regulated by feedback. ![]() Measurements obtained include the amplitude of the light reflex, latency ( 13), velocity (peak or average) ( 14) and acceleration ( 15), all of which show wide variation in the healthy population. A more rigorous assessment of the PLR is now possible using pupillometric measurements using infrared video techniques. In addition to this variability in resting pupil size, clinically there is wide variation in the dynamic pupillary light reflex (PLR) in healthy individuals. Although it was previously believed that pupil size may decrease significantly after cataract surgery, more recent literature suggests the reduction in size is temporary and returns to preoperative levels by 1 month ( 12). Different classes of glaucoma medication also influence pupil size ( 1). This inverse correlation between age and resting pupil size has been confirmed pre-operatively in refractive surgery candidates across a range of different luminance levels ( 8, 9), but the effect seems to be most marked at low luminance suggesting that it is due to a progressive decline in sympathetic tone throughout adult life ( 7, 10).Ĭertain medical conditions such as diabetes and pseudoexfoliation can also decrease the effect of dilating drops on the size of the pupil ( 11). At a population level it has also been shown that pupils tend to be smaller with increasing age ( 7). Many studies have evaluated this variation in pupil size in different illumination levels, suggesting pupil size decreases in a linear manner for each luminance level ( 6). In any individual person pupil size is influenced by a number of factors including ambient light, retinal sensitivity, central cognitive processes ( 2, 3), alertness and emotional unrest ( 4, 5) with pupil measurements additionally being used by researchers as a biomarker of activity in the autonomic nervous system- both in health and in disease. In the healthy population there is significant variation in the resting size of the pupil and in the reflex constriction of the pupil to light. Pupil size is governed by the opposing actions of the iris sphincter and dilator muscles under the control of the parasympathetic and sympathetic nerves, respectively. Pupil size is important not only because it controls the amount of light that is able to reach the retina but also because it affects the levels of chromatic and spherical aberration, thereby optimising visual perception ( 1). Future studies to identify these genetic factors could improve our understanding of variation in pupil size and pupillary reactions in health and disease. PLR amplitude, latency and constriction velocity had estimated heritabilities of 69% (95% CI 54–79%), 40% (95% CI 21–56%), and 64% (95% CI 48–75%), respectively.Ĭonclusion: Genetic effects are key determinants of resting pupil size and reactivity. ![]() In darkness the resting pupil size showed a MZ intraclass correlation coefficient of 0.85, almost double that of DZ (0.44), suggesting strong additive genetic effects, with the most parsimonious model estimating a heritability of 86% with 14% (95% CI 10–21%) explained by unique environmental factors. Pupil size and PLR were not associated with iris colour, intraocular pressure or refractive error, but were associated with age (diameter β = −0.02, p = 0.016, constriction amplitude β = −0.01, p < 0.001, velocity β = 0.03, p < 0.001, and latency β = 0.98, p < 0.001). ![]() Pupil light reaction (PLR) had a mean (SD) amplitude of 1.38 mm (0.27) and latency of 250.34 milliseconds (28.58). Results: Mean (SD) pupil diameter in darkness was 5.29 mm (0.81), decreasing to 3.24 mm (0.57) in bright light. Maximum-likelihood structural equation models estimated the proportion of trait variance attributable to genetic factors. Methods: Pupillometry was performed on 326 female twins (mean age 64 years) from the TwinsUK Adult Twin Registry, assessing resting pupil diameter in darkness and increasing levels of ambient light, alongside dynamic pupillary characteristics. Purpose: A classic twin study to evaluate the relative contributions of genetic and environmental factors to resting pupil size and reactivity. 3Department of Neuro-Ophthalmology, National Hospital for Neurology and Neurosurgery, London, United Kingdom.2Department of Ophthalmology and Epidemiology, University Medical Centre Groningen, University of Groningen, Groningen, Netherlands.1Section of Academic Ophthalmology, School of Life Course Sciences, Faculty of Life Sciences & Medicine, King's College London, London, United Kingdom.Abdus Samad Ansari 1, Jelle Vehof 1,2, Christopher J. ![]()
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |