Seeing the future: predictive control in neural models of ocular accommodation

Ocular accommodation is the process of adjusting the eye's crystalline lens so as to bring the retinal image into sharp focus. The major stimulus to accommodation is therefore retinal defocus, and in essence, the job of accommodative control is to send a signal to the ciliary muscle which will minimise the magnitude of defocus. In this paper, we first provide a tutorial introduction to control theory to aid vision scientists without this background. We then present a unified model of accommodative control that explains properties of the accommodative response for a wide range of accommodative stimuli. Following previous work, we conclude that most aspects of accommodation are well explained by dual integral control, with a "fast" or "phasic" integrator enabling response to rapid changes in demand, which hands over control to a "slow" or "tonic" integrator which maintains the response to steady demand. Control is complicated by the sensorimotor latencies within the system, which delay both information about defocus and the accommodation changes made in response, and by the sluggish response of the motor plant. These can be overcome by incorporating a Smith predictor, whereby the system predicts the delayed sensory consequences of its own motor actions. For the first time, we show that critically-damped dual integral control with a Smith predictor accounts for adaptation effects as well as for the gain and phase for sinusoidal oscillations in demand. In addition, we propose a novel proportional-control signal to account for the power spectrum of accommodative microfluctuations during steady fixation, which may be important in hunting for optimal focus, and for the nonlinear resonance observed for low-amplitude, high-frequency input. Complete Matlab/Simulink code implementing the model is provided at https://doi.org/10.25405/data.ncl.14945550

Improvement in impaired ocular accommodation by parietal acupoint therapy to relieve neck stiffness: a case report

ObjectivesNeck stiffness could lead to impaired ocular accommodation. We report two cases that visual function was improved by relieving neck stiffness.Case presentation(Case 1) A 34-year-old female complained of neck stiffness and visual problems after computer work. She was treated by parietal acupoint therapy (PAPT), which is a new scalp micro-acupuncture system. The evaluation of accommodative micro-fluctuations (the Fk-map) showed that increased bilateral ciliary muscle tension in the middle to near distance was relieved bilaterally, accompanied by relief of neck stiffness after treatment. (Case 2) A 43-year-old female complained of a visual problem with pressure pain on the bilateral posterior cervical muscles. Performing with PAPT improved impaired ciliary muscle tension noticeably with relief of neck stiffness after treatment.ConclusionsThis is the first report on the improvement of impaired ocular accommodation with treating neck stiffness by using PAPT.

Effect of spectral overlays on visual parameters and reading ability: an integrative review

ABSTRACT Purpose: to provide an integrative review of indexed articles published from 2009 to 2019 on the effect of spectral overlays on visual parameters and reading ability. Methods: keywords were used to search seven databases. Duplicate entries, reviews, literature reviews, editor's comments, and congress abstracts were excluded, as well as papers that were not relevant, based on their titles and abstracts. A total of 52 articles, which were read in full, were eligible at this stage. Of these, 12 articles, published in Portuguese or English from 2009 to 2019, were included. Results: all 12 articles included evaluated the effect of overlays on the reading rate. There was an improvement in different visual parameters (ocular accommodation and eye movement), facial recognition, and reading (reading rate, relative efficiency, and comprehension). The use of overlays reduced visual stress regardless of refractive, orthoptic or cognitive disorders. The associated conditions investigated were autism spectrum disorder, Tourette syndrome, stroke, deafness, dyslexia, and auditory temporal processing disorder. Conclusion: the effectiveness of overlays in improving reading quality is consistently demonstrated in the literature. The reviewed articles showed that the overlays’ effect is more expressive when the visual stress is associated with conditions that present sensory alterations and cortical hyperactivity.

Crystalline lens imaging during accommodation with a slit-scanning tomography system: preliminary results

A slit-scanning tomography system previously developed in the Centre of Physics of University of Minho allows to capture images of the eye and posteriorly calculus of the biometric (thickness and curvature) and optical (wavefront aberrations) properties of the corneal and crystalline lens surfaces. It is intended to optimise the system for an accurate computing of these properties of the crystalline lens in the relaxed state and during ocular accommodation. In this study, preliminary experimental results of the crystalline lens imaging of a subject during accommodation are presented.

The prevention and treatment of myopia in schoolchildren from grade 1 to grade 10 by restoring the ocular accommodation function

Purpose: to evaluate long term effectiveness of a method of restoring the accommodation function of the eye and preventing the onset and progression of myopia and to propose ways to overcome medical requirements that are difficult to meet.Material and methods. The method consisted in prolonged installations of 1 % tropicamide eye drops and permanent optical correction that corresponded to manifest refraction. 48 schoolchildren aged 7–18 with initial myopia or signs of high risk myopia onset were followed up. The subjects were divided into 2 groups of 24 people each. Group 1 consisted of children who followed medical prescriptions and group 2 consisted of those who did not. The two groups were further subdivided into two subgroups. Subgroup 1A included 12 children with the initial positive cycloplegic refraction up to +1.0 D; subgroup 1B included 12 children with the initial negative cycloplegic refraction from -0.5 D. Subgroup 2A (12 children) had negative cycloplegic refraction who regularly failed to receive treatment (optical correction, eyedrop instillations, medical checkups), and subgroup 2B (12 children) had negative cycloplegic refraction who received practically no treatment for myopia. Regular checkups took place 2–3 times a year for 10 years and included measuring visual acuity, manifest and cycloplegic refraction by skiascopy or subjectively, as well as measuring relative accommodation reserve (RAR) according to the author’s own technique. The treatment envisaged permanent optical correction in accordance with manifest refraction until the age of 18 years, combined with courses of tropicamide 1 % instillations for 1 to 3 months two to three times a year. Results. In group 1A, myopia was prevented in all subjects. In group 1B, the progression stopped after several years of treatment. In subgroup 2A and especially subgroup 2B, myopia progressed, over the 10-year follow-up period reaching the figures of 2.5 and 3.5 D, respectively. Conclusion. The long-term efficiency of the proposed method applied to schoolchildren from grade 1 to grade 10 was confirmed. Ways to overcome the difficulties of following medical requirements were proposed.

Whole Eye Optical Coherence Tomography Imaging

Many eye diseases will affect the shape and dimensions of the whole eye. For examination of ocular accommodation and pathological changes caused by these diseases, high resolution imaging of the whole eye segments OCT system is needed. However, limited by the imaging depth, traditional Fourier Domain Optical Coherence Tomography (FDOCT) can’t be used for real time whole eye segment imaging. In recent years, techniques for depth extended FD-OCT system especially for whole eye segment imaging has been developed. Application on eye parameters measurement and eye accommodation studies were successfully performed. In this paper, both of whole eye FD-OCT techniques and their application were reviewed. Potential clinical application of these techniques may be in the detection of the pathological changes of the whole eye, and whole eye segment FD-OCT system also provides a powerful imaging method for ophthalmic research, such as accommodation, ocular growth, and biometry of the eye.