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An Approach to Pupillary Disorders
Published in Vivek Lal, A Clinical Approach to Neuro-Ophthalmic Disorders, 2023
Sarosh M. Katrak, Azad M. Irani
The pupillary constrictor muscle is innervated by the parasympathetic neurons. The preganglionic fibers originate in the ipsilateral Edinger-Westphal nucleus in the tectum of the midbrain. The fibers course ventrally through the midbrain to emerge in the interpeduncular fossa along with other fibers of the oculomotor nerve. These parasympathetic fibers remain dorsal and superficial throughout the course of the third cranial nerve in the subarachnoid space. Hence, these fibers are more susceptible to extrinsic compression (e.g., posterior communicating artery aneurysm) and relatively protected from ischemic insults as the vasa nervorum lies deep within the substance of the oculomotor nerve. These preganglionic parasympathetic fibers terminate in the ciliary ganglion within the orbit. Postganglionic parasympathetic fibers pass through the sclera as the short ciliary nerves and innervate the pupillary constrictor fibers (Figure 14.2). Activation of its muscarinic (M3) cholinergic receptors produces constriction or miosis of the pupil. An interesting anatomical fact is that only 3–5% of these fibers terminate in the iris sphincter muscle. The remainder terminate in the ciliary muscles that control accommodation [2]. The importance of this will be discussed later.
Panax quinquefolium (American Ginseng) and Physostigma venenosum (Calabar Bean)
Published in Azamal Husen, Herbs, Shrubs, and Trees of Potential Medicinal Benefits, 2022
Sushweta Mahalanobish, Noyel Ghosh, Parames C. Sil
Glaucoma, an ophthalmic disease, is characterized by optic nerve damage due to high intraocular pressure and resulting vision loss. In 1885, Adolf Weber suggested glaucoma as an optic neuropathy. In 1864, physostigmine was used as the first herbal remedy of glaucoma progression (Orhan et al., 2011). The acetylcholinesterase inhibitory property of physostigmine increases the free acetylcholine level on the muscarinic receptors m2 and m3 in the pupil sphincter. Consequently, there is increased accommodation due to contraction of the circular portion of the ciliary muscle. In case of glaucoma, it works like an ocular hypotensive agent. Physostigmine releases excess aqueous humor from the trabecular pathway by inducing the contraction of the longitudinal portion of the ciliary muscle (Pinheiro et al., 2018). However, use of physostigmine leads to a couple of side effects including headache, blurred vision, retinal detachment, inflammation of cornea, iris as well as conjunctiva, which limits its application in glaucoma (Pinho et al., 2013). Figure 10.6 represents the health benefits of CB.
Ageing
Published in Henry J. Woodford, Essential Geriatrics, 2022
Around 13% of people aged over 75 are visually impaired (defined as scoring < 6/18 on Snellen acuity testing).68 Age-related changes include reduced lens flexibility and altered light refraction, cataract formation, reduced ciliary muscle contractility, macular degeneration, reduced eye movements and slower visual processing. Presbyopia is a term for the loss of accommodation seen with advancing age. It is caused by changes in the lens and ciliary muscle, which can usually be corrected with glasses. Binocular visual loss is related to refractive errors in around 32% of affected people.68 The commonest eye diseases affecting vision in older age are age-related macular degeneration (AMD) (36% of those with visual impairment), cataracts (25%), glaucoma (8%) and diabetic retinopathy (2%).
Comparison of Retinal and Choroidal Microvasculature Changes in Monocular Amblyopic and Non-amblyopic Eyes following Short-term Patch Occlusion Treatment
Published in Current Eye Research, 2023
Jae-Gon Kim, Se Youp Lee, Dong Cheol Lee
Furthermore, it is possible that patch occlusion treatment leads to a proportional increase in the stromal area, concomitant with a reduction in the luminal area. Increasing the stromal area, which consists of non-vascular smooth muscle cells involved in accommodative functions,32,39 during patch occlusion treatment may restore some functionality that is diminished in the amblyopic eye40 compared to the non-amblyopic eye. This improved accommodation can lead to better visual acuity.40 Overall, improved BCVA may be attributed to multiple factors, including increased synaptic connections in the OPL, improved photoreceptor function, dark adaptation-induced choroidal vasoconstriction, and increased non-vascular smooth muscle cells in the stroma.
Less is more: optimal recording time for measuring the steady-state accommodative response
Published in Clinical and Experimental Optometry, 2023
Beatríz Redondo, Jesús Vera, Rubén Molina, Raimundo Jiménez
Accommodation is the active dioptric power change of the eye to maintain a clear image of an object on the retina. There are subjective and objective techniques for measuring the accommodative function, with subjective methods relying on the patient’s perception of blur as an end point criterion, whereas objective methods are primarily based on the assessment of the optical power or refractive status of the eye.1 Objective methods, based on ocular refractometry, provide a more reliable and accurate measure of accommodation, since subjective measures seem to overestimate the accommodative function.2–4 Most autorefractors only measure the distance static refractive error while the eye focuses on internal fixation targets, and these devices have shown to cause instrument myopia.5 However, accommodation is a dynamic process, which requires focus on targets located at different accommodative demands, and fluctuates throughout time when focusing on a stationary target.6
Visual function impairment in patients suffering from visually induced motion sickness. A preliminary observational longitudinal study
Published in Hearing, Balance and Communication, 2023
Leonardo Gabriele, Sara De Angelis, Vittorio Roncagli, Marco Tramontano, Leonardo Manzari, Domenico Gabriele
Two evaluation sessions were carried out immediately before (T0) and after 16 weeks of visual rehabilitation training (T1) (Figure 1). Each evaluation aimed to evaluate participants’ visual function and sickness-related symptoms. Visual function evaluation consisted of vergence and accommodative tests, binocular vision, stereopsis and phoria. The function of the vergence eye movement system is to track objects moving in depth, to attain cortical fusion and bifoveation. Visual accommodation is a reflexive physical process in which the lens of the eye adjusts allowing images to become focussed. The stereopsis is the perception of depth produced by the reception in the brain of visual stimuli from both eyes in binocular vision. The phoria is characterized by a latent horizontal and vertical deviation of the visual axes.