Visual Impairment

More than severe than visual impairment, legal blindness is defined as "a visual acuity of 20/200 or a visual field of 20 degrees or less" according to the World Health Organization (2016) classification of diseases and related wellness problems.

From: Reference Module in Biomedical Sciences , 2021

Introduction to Middle Infections

John E. Bennett MD , in Mandell, Douglas, and Bennett'southward Principles and Practice of Infectious Diseases , 2020

Visual Acuity and Measuring Low Vision

The ophthalmologist's notation usually starts with a measurement of visual acuity. This is measured both "with correction" and "without correction," meaning correction of refractive error (e.g., through use of spectacles). A "pinhole" visual acuity is measured by having the patient expect through a card with a pinhole in information technology. This mimics optimal refraction and distinguishes visual loss due to uncorrected refractive fault from more serious etiologies.

Patients with low vision are specially afflicted by lighting conditions, and the non-ophthalmologist should keep this in listen. Patients existence examined at the bedside in a dimly lit infirmary room may have better vision when examined nether good lighting.

The all-time visual acuity the patient tin achieve with each eye is ever recorded. Patients with serious eye infections may have worse vision than can be measured with the Snellen eye chart; the "big E" at the elevation of the chart is 20/400 vision. If the patient has very low vision, information technology is recorded as one of the following, in descending gild: "count fingers" (CF), "mitt motility" (HM), or "calorie-free perception" (LP). For count fingers vision, the distance of the examiner's fingers is recorded, then "CF at 3 feet" is recorded and represents better vision than "CF at i foot." If the patient cannot detect a bright light shining directly in his or her eye, he or she has "no light perception" (NLP) vision, or complete incomprehension in that centre. Visual recovery from NLP is extremely unlikely in an infected middle unless the NLP recording is transient. Any vision meliorate than NLP is worth saving, and an aggressive arroyo to eye infections is important; patients value even LP vision. In addition, there are many factors that affect vision in the setting of an astute eye infection, and some of these are reversible. The patient's vision 3 months after an astute bacterial endophthalmitis, for example, is usually much improve than it is 3 days after presentation.

Visual Impairment

W. Sapp , in International Encyclopedia of Education (Third Edition), 2010

Etiologies of Visual Impairments and Their Impact

Before discussing the implications of visual impairments, it is important to sympathize several key concepts: definitions of fundamental terms related to visual impairments, the nearly prevalent etiologies of visual impairments, and the functional implications of different types of visual impairments.

Definitions

Visual impairments include low vision and blindness and refer to whatever degree of harm to a person's ability to encounter that affects his or her daily life. Blindness technically refers to a total absenteeism of vision, although the term is often used to refer to severe visual impairments that result in a need for primarily using nonvisual sensory information. Low vision refers to visual impairments that are less severe than incomprehension simply yet impact a person's ability to consummate daily activities to some degree. People with low vision may need to use tools and techniques to heighten their ability to use their limited vision, or they may demand to utilise nonvisual ways for completing tasks.

Etiologies and Prevalence

The rate of visual impairments in children in wealthy nations is approximately 1–two per 1000 children with only approximately i in 10  000 having a severe visual impairment or total blindness. In developing countries, the rates of severe visual impairments are estimated to exist 10 times higher than in wealthier nations, occurring at a rate of one in k children (Gilbert et al., 1999).

The about prevalent types of visual impairments vary depending on age and geographic location. For children in developing countries, the most prevalent forms of visual impairments are vitamin A deficiency, corneal scarring, trachoma (an eye infection), inherited conditions, and onchocerciasis (river blindness caused by a parasitic worm that lives in contaminated waterways) (Gilbert et al., 1999; Roodhooft, 2002). With the exception of inherited weather condition, all of these causes of visual impairments are preventable through proper diet, hygiene, and medical care. Unfortunately, many children in developing countries do not accept access to these basic needs that would foreclose their visual impairments.

In wealthier nations where basic nutrition, sanitation, and healthcare are more readily available, different causes event in most childhood visual impairments. In the Usa, the most common causes of visual impairments in children are cortical vision impairment, optic nervus hypoplasia, retinopathy of prematurity, albinism, and abnormalities in the structures of the eye (Hatton and Model Registry of Early Childhood Visual Impairment Collaboration Group, 2001). Some of these causes of visual impairment are often associated with the presence of additional disabilities (e.g., cortical visual harm) and the rates of these etiologies have increased as medical care allows children with more than severe disabilities and children born with extremely low nascency weights to survive.

Functional Implications

Visual impairments impact many aspects of seeing. Most visual impairments are the event of damage to one or more than structures in the eye. When the middle is damaged, there can exist reduced acuity (clarity of what is seen), reduced visual fields (e.g., tunnel vision or bullheaded spots), reduced ability to encounter color or dissimilarity, or difficulty with lighting and glare, or some combination of these problems. Visual impairments, such equally cortical vision impairment and optic nerve hypoplasia, are the result of a poorly adult or damaged optic nervus or visual cortex. These conditions can take any or all of the problems associated with damage to the middle; and additionally, there is difficulty in the encephalon receiving and processing visual information.

Coupled with the causes of visual impairments and the differing impacts on vision that can occur, a major factor in the needs of a person with visual impairments is based on when the visual impairment first occurred. Adventitious visual impairments occur after a child or teen has lived with typical vision for many years, benefiting from visual information to understand and interact with his or her globe. Children who feel an adventitious visual damage have to accommodate psychologically to the vision loss and learn new ways to practice things they already knew how to do (eastward.g., dressing, reading, and eating). Congenital visual impairments occur at nativity or when a kid is very young. Children with congenital visual impairments develop their concepts about the world with limited or no visual input. Vision typically helps children unify the information they receive through their other senses and helps them gather vast amounts of information more quickly than they can do with other senses. When vision is absent or impaired in the early years, children demand intentional interactions with their globe to develop logical and accurate concepts.

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Multiple Sclerosis and Other Inflammatory Demyelinating Diseases of the Cardinal Nervous Organization

Joseph Jankovic MD , in Bradley and Daroff'due south Neurology in Clinical Practice , 2022

Impairment of Visual Pathways

ON, inflammation at any signal of the optic nerve, is common at some signal in the course of patients with relapsing MS, and frequently it may be the presenting symptom. The optic nerve is the nearly commonly affected site of the visual pathway. It usually manifests as an astute or subacute unilateral syndrome characterized by pain in the eye that is accentuated by ocular movements, followed by a variable degree of visual loss affecting mainly central vision and sometimes decreased colour vision as well. Patients with ON often take a relative afferent pupillary defect (Marcus Gunn pupil) and most take a normal fundoscopic exam; papillitis is rarely seen. Mapping of visual fields reveals a central or cecocentral scotoma (fundamental scotoma involving the physiological blind spot). Later an attack of acute ON, 90% of patients regain normal vision, typically over a flow of 2–6 months.

It is important to note that bilateral, simultaneous ON is rare in MS, and its occurrence may suggest another diagnosis such as Leber hereditary optic neuropathy, toxic optic neuropathy, neuromyelitis optica, or anti-MOG antibody associated ON. In bilateral ON in MS cases, the damage normally begins asymmetrically and is more severe in ane eye.

Visual Loss

Robert A. Avery , in Liu, Volpe, and Galetta'south Neuro-Ophthalmology (3rd Edition), 2019

Treatment

Visual loss is the best indication for intervention, which is primarily neurosurgical. In some instances preoperative embolization facilitates removal, given the hypervascularity of these lesions. 292 Pterional or subfrontal craniotomies are the virtually popular surgical approaches. When the tumor is densely adherent to the internal carotid or anterior cerebral arteries or the anterior visual pathway, a subtotal resection is recommended. 291 Smaller, less-complicated sellar meningiomas may exist removed transsphenoidally using endoscopic techniques. 293 External beam radiation (5000–5500 cGy) 294 or gamma-pocketknife stereotactic radiosurgery 295 should be considered when there is residual or recurrent tumor or when surgery is contraindicated.

Alternatively, observation may be the all-time approach in some cases. Elderly patients or poor operative candidates with mild to minimal visual loss, for example, may be amend off with conservative management. 296 Hormonal therapy may be another pick when tumors recur despite surgery or radiations, when they become unresectable because of location, or when these traditional approaches are contraindicated. 297 Experience with suprasellar meningiomas, withal, is limited, 298 and some hormonal treatments such as RU-486 are poorly tolerated because of a flulike side-effect.

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Age-Related Macular Degeneration : Non-Neovascular Early AMD, Intermediate AMD, and Geographic Cloudburst

Andrew P. Schachat MD , in Ryan's Retina , 2018

Management of Visual Damage From NNVAMD

Among patients with unilateral or bilateral avant-garde non-neovascular AMD, as well as those with vision impairment attributed to nongeographic cloudburst, noncentral GA, or confluent foveal drusen or drusenoid PED, rehabilitation with a low-vision service should exist considered. Experienced eye care and social service professionals can decide what services or devices might help the individual optimize the vision office and simultaneously adjust and cope with their vision harm. Issues specific to driving may need to exist considered.

In phakic patients with bilateral advanced and endstage untreatable AMD (central GA or stable disciform scar from NVAMD), consideration can exist given for implanting a visual prosthetic device, likewise referred to as an implantable miniature telescope (IMT; VisionCare Ophthalmic Technologies, Saratoge, CA) (Fig. 68.48). 202 This device provides ii.2 to iii times magnification of the cardinal visual field and affords approximately two times the field of view of that associated with a similar strength external telescope. A prospective, open-label, multicenter clinical trial of 217 participants (age 55–93) with bilateral central visual acuity loss (twenty/80-twenty/800) related to key GA or stable disciform scars evaluated the device, limiting inclusion to individuals that prior to enrollment demonstrated at least a 5-letter improvement with an external telescope. Furthermore, study participants may have experimented with an external telescope for several days at dwelling house to evaluate the loss of binocularity and peripheral vision that comes with utilise of a telescope. The fellow eyes of these individuals were used as the command groups, they did non receive the implant, and the young man eye was expected to provide peripheral vision for the participant. A full of 206 (95%) of 217 eyes were implanted with the device, every bit 11 procedures were aborted at the fourth dimension of surgery. Two devices (ane%) required removal one month after placement due to condensation within the telescopic cylinder due to device damage at the time of implantation. 202 Postoperatively, the patients were asked to participate in six visual rehabilitation sessions to learn how to suit to use of the telescope in daily life. These visits included training in learning to utilize alternating viewing between eyes for peripheral and primal tasks. Amid the 192 implanted eyes for which i-yr follow-upward information was reported, 67% of implanted optics gained at least 3 lines of distance visual acuity every bit compared to 13% of the swain eyes. An improvement of at least 3 lines at both altitude and near occurred in 53% with the IMT vs. ten% of young man eyes. 202 Safety concerns at ane twelvemonth included the ascertainment that five% experienced at least a ii-line visual acuity loss at distance or most. In addition, mean endothelial cell decease following implantation of the device was 20% at 3 months and 25% at 12 months. 202 A potential limitation of this study was the lack of a control group that received intensive vision rehabilitation in the absence of the IMT, so the extent to which a placebo effect is associated with the device and the intensive rehabilitation are responsible for the study results is unknown.

Visual Impairment

Ellen East. Freeman , Emily W. Gower , in Women and Health (Second Edition), 2013

Measurement of Visual Damage

Visual impairment is most often defined by visual acuity. Visual acuity measures the spatial resolving power of the visual system. For research purposes, visual acuity is typically measured using the Early Treatment of Diabetic Retinopathy Report letter chart ( Figure 99.2) under standardized conditions. This chart consists of 14 rows with 5 letters per row and covers a 20-fold range of letter of the alphabet size. The progression of letter height from line to line is geometric with a 0.1   log unit divergence per line. The difficulty scores of the ten letters chosen for the chart are approximately equal. I tin either measure best-corrected visual acuity, in which the consequence of any refractive error is removed, or presenting visual acuity, which does not remove the outcome of any refractive error. Visual acuity is oft recorded as a fraction with the numerator indicating the test distance of the chart in feet. The denominator indicates the altitude at which a 'normal' heart could meet the smallest letters that the centre being tested can see. For case, if someone is determined to have 20/40 vision, the smallest letters they tin can meet at 20 feet are the size of letters that a 'normal' middle could see at 40 anxiety. Thus, the bigger is the denominator, the worse the vision. For research purposes, visual acuity worse than 20/40 (six/12 in meters) indicates visual impairment, while the Globe Health Arrangement uses a threshold of 20/sixty (six/18 in meters).

Figure 99.2. ETDRS chart to measure visual acuity.

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Visual Loss

Grant T. Liu , ... Steven 50. Galetta , in Liu, Volpe, and Galetta's Neuro-Ophthalmology (Third Edition), 2019

History

Common complaints encountered with visual loss include so-called negative phenomena such as "blurry vision" or "grayness vision." Patients with higher cortical disorders may have nonspecific complaints such equally "I'grand having trouble seeing" or "Focusing is hard." Patients with lesions of the afferent visual pathway may likewise complain of positive phenomena, such as flashing or colored lights (phosphenes or photopsias), jagged lines, or formed visual hallucinations (a faux perception that a stimulus is present). The complexity of positive phenomena does not specify localization.

The temporal profile of the visual loss volition advise possible diagnoses, and its monocularity or binocularity will help in localization. As a general rule, acute or subacute visual deficits result from ischemic or inflammatory injury to the optic nerve. Vitreous hemorrhage and retinal detachment are other important considerations. Chronic or progressive visual loss, in turn, may result from a compressive, infiltrative, or degenerative process. Cataracts, refractive error, open-bending glaucoma, and retinal disorders such as age-related macular degeneration or diabetic retinopathy besides need to be considered when visual symptoms are insidious.

If a patient complains of monocular visual loss, a process in one middle or optic nerve should be considered. Painless transient visual loss characterized by a "greyness shade" that encroaches on vision superiorly then resolves after seconds or minutes is typical of amaurosis fugax related to carotid disease. Painful monocular visual loss occurring over days is characteristic of an inflammatory or demyelinating optic neuropathy. With binocular visual loss, a lesion of both eyes or optic fretfulness, or of the chiasm, tract, radiation, or occipital lobe, should be investigated. Further details regarding these specific complaints and their localizing value are provided in the corresponding chapters.

Associated neurologic deficits, such as motor or sensory abnormalities, will also help in localization and oft indicate a hemispheric abnormality. Medical conditions should e'er exist investigated in the review of systems. Hypertension, diabetes, and smoking, for example, predispose the patient to vascular disease, and a history of coronary avenue affliction should warning the examiner to the possibility of carotid artery insufficiency as well. Visual loss accompanied by endocrine symptoms, such as those consistent with hypopituitarism (amenorrhea, decreased libido, or impotence, for example) or pituitary hypersecretion (galactorrhea or acromegaly, for example), suggests a chiasmal disorder.

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Vision loss

Grant T. Liu MD , ... Steven L. Galetta Doc , in Neuro-Ophthalmology (Second Edition), 2010

Chiasmal trauma

In the setting of blunt head trauma, vision loss much less commonly localizes to the chiasm than to the optic nervus. Nonetheless, a traumatic chiasmal syndrome is well recognized. Blunt frontal head trauma is the usual crusade, and patients wake up with a nonprogressive bitemporal hemianopia, oftentimes complete. 558 Common associated findings include ocular motion deficits, anosmia, deafness, CSF rhinorrhea and otorrhea, and diabetes insipidus due to trauma to the pituitary stalk. 559 In a few instances see-saw nystagmus is related to chiasmal trauma. 35 Neuroimaging may reveal longitudinal disruption of the chiasm ( Fig. 7–38 ). 560 , 561 The machinery of the bitemporal hemianopia is unclear, and proposed theories include stretching of the body of the chiasm, 559 a vascular insult, or contusion hemorrhage, necrosis, or tears. 562 Two patients with traumatic chiasmal syndrome were found to take midline basilar skull fractures through the midclivus, sella turcica floor, dorsum sellae, and sphenoid sinus, suggesting the chiasm was torn. 558 One instance following autoenucleation and removal of the optic nervus and half of the chiasm has likewise been reported. 563

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Vision loss

Grant T. Liu Medico , ... Steven L. Galetta MD , in Neuro-Ophthalmology (2d Edition), 2010

Symptoms

The presence of metamorphopsia or photopsia may be very helpful in localizing vision loss to the retina. Patients with metamorphopsia describe warping, bending, or crowding of the images, while those with photopsia complain of seeing sparkles of light. Both of these symptoms are very unusual in optic neuropathies. The complaint of light incomprehension or aberrant glare sensitivity (hemeralopia) also suggests the presence of retinal dysfunction and may exist a prominent symptom in patients with cone dysfunction. In dissimilarity, patients who observe a darkening of their vision or loss of color perception usually have optic nerve disease. Night vision loss, or nyctalopia, tin commonly accompany widespread retinal photoreceptor disease. Other symptoms that accompany the vision loss may provide distinguishing features. For instance, hurting in clan with vision loss is exceedingly uncommon in patients with retinal problems, but may accompany optic affliction, particularly inflammatory atmospheric condition such equally optic neuritis.

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Visual loss

Grant T. Liu Doc , ... Steven L. Galetta MD , in Neuro-Ophthalmology (Second Edition), 2010

Specific toxic optic neuropathies

Methanol. Methanol is a well-recognized optic nerve toxin and can cause profound vision loss even in small doses. The presentation is quite unlike from other toxic optic neuropathies considering patients may develop sudden vision loss with disc swelling, and they may exist comatose with metabolic acidosis. Patients are typically inebriated, and then inside 18–48 hours develop headache, dyspnea, vomiting, abdominal pain, and bilateral visual blurring. Visual symptoms initially may exist transient. Patients may have ingested methanol in a suicide endeavor or every bit an inadvertent contaminant in bootleg alcohols. Benton and Calhoun 1048 reported the largest series of patients (n = 320) who ingested methanol as a contaminant of homemade whiskey.

The astute optic disc edema is indistinguishable from papilledema. Disc swelling has been demonstrated in experimental methanol poisoning in monkeys, 1049 and results from axoplasmic stasis secondary to demyelination and axoplasmic obstruction. 1050 The pathogenesis of these changes is presumed to be a histotoxic anoxia occurring in a vascular watershed. 1050 Although the bulk of the damage is believed to result from demyelination of the retrolaminar optic nervus, 1050 , 1051 electrophysiologic studies suggest additional widespread photoreceptor and Mueller cell dysfunction. 1052 Treatment is aimed at the acidosis and includes dialysis and intravenous ethyl booze, which interferes with methanol metabolism. Morbidity is high, and the prognosis for visual recovery is poor. Optic atrophy develops and tin be accompanied by cupping. 958

Ethambutol. Ethambutol causes a dose-related optic neuropathy and was recognized as an optic nervus toxin soon afterwards its introduction as a treatment for tuberculosis. In one large series of 800 patients taking ethambutol, 1.5% adult a toxic optic neuropathy. 1053 The toxicity is thought to result from its chelating properties. A typical presentation includes either cardinal field defects with loss of vigil and dyschromatopsia or well-preserved central visual function with peripheral visual field loss. 1054 Chiasmal-type central bitemporal field loss may too occur. Vision loss is not accompanied past other neurologic symptoms. Doses less than 15 mg/kg/day are thought to be prophylactic, but in patients taking between fifteen and 25 mg/kg/day visual symptoms generally develop over a period of months. 1054 , 1055 More severe and irreversible vision loss has been reported in patients treated with ethambutol for renal tuberculosis. 1056 Dyschromatopsia (particularly for green) and loss of contrast sensitivity are reported to exist early signs of visual loss. 1057 OCT measurements of the nerve fiber layer tin be used to follow patients and may predict recovery in the setting of normal measurements. 1058 , 1059 Some visual improvement typically occurs with discontinuation of the drug simply abnormalities in the visual fields and contrast sensitivity may persist. 1060 Older patients may exist less likely to recover. 1061

Amiodarone. An optic neuropathy with disc swelling very similar to anterior ischemic optic neuropathy has been reported in patients taking the anti-arrhythmia drug amiodarone. 1062–1071 Contend even so exists as to whether this is a true toxic optic neuropathy acquired past amiodarone versus ordinary ischemic optic neuropathy. Most bear witness for the status comes but from case reports, and the only prospective study of over 800 patients taking amiodarone suggested the incidence of the condition to exist at well-nigh 0.1%. 1072 The patient population taking the drug is likely to be vasculopathic and at risk for ordinary ION, further clouding the outcome. However, some clinical features may distinguish amiodarone-associated optic neuropathy from ION. 1070 For example, visual loss may exist insidious over months, ofttimes with bilateral simultaneous involvement of the eyes, and is unremarkably less severe than in ordinary ION. 1062,1064,1073,1074 The disc swelling may final for months, and some recovery can be associated with discontinuation of the drug. 1066 Aberrant lamellar inclusions in optic nervus axons accept been identified on histopathologic study. 1063

Halogenated hydroxyquinolines. Halogenated hydroxyquinolines have been implicated in the development of myelopathy and optic neuropathy (subacute myelo-optic neuropathy; SMON). The drug was used to forbid diarrhea when traveling and for other gastrointestinal symptoms. The condition has largely been reported in Nippon. 1075 Patients develop optic atrophy with severe vision loss which may exist partially reversible with discontinuation of the drug.

Tumor necrosis factor-α inhibitors. Optic neuritis has been reported equally a complexity of TNF-α inhibitors used to care for juvenile idiopathic 1076 and rheumatoid arthritis. 1077 It is not certain whether the optic neuritis was caused by the drugs or whether the vision loss occurred equally a outcome of the underlying disease.

Other toxic optic neuropathies . As more drugs are adult to treat neoplasms, an increasing number of optic nerve toxins take been identified. In some instances multiple drug regimens for chemotherapy and bone marrow transplantation are associated with optic neuropathy, and the specific crusade cannot be identified. 1078 Interferon-α used to treat hepatitis too as certain cancers may be associated with an ION-like optic neuropathy. The optic neuropathy is often bilateral and may recur after the drug is restarted. 1079–1083 The list of other drugs reported to cause toxic optic neuropathy is long and is summarized in Table v–nineteen . The table does not describe every reported optic nerve toxin but supplements the discussion to a higher place with some of the more than commonly encountered ones.

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