Visual impairment

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Visual impairment
Classification and external resources
Hyperopia.gif
ICD-10 H54
ICD-9 369

Visual impairment (or vision impairment) is vision loss (of a person) to such a degree as to qualify as an additional support need through a significant limitation of visual capability resulting from either disease, trauma, or congenital or degenerative conditions that cannot be corrected by conventional means, such as refractive correction or medication.[1][2][3] This functional loss of vision is typically defined to manifest with

  1. best corrected visual acuity of less than 20/60, or significant central field defect,
  2. significant peripheral field defect including homonymous or heteronymous bilateral visual, field defect or generalized contraction or constriction of field, or
  3. reduced peak contrast sensitivity with either of the above conditions.[1][2][3][4]

Eye disorders which can lead to visual impairments can include retinal degeneration, albinism, cataracts, glaucoma, muscular problems that result in visual disturbances, corneal disorders, diabetic retinopathy, congenital disorders, and infection." Visual impairment can also be caused by brain and nerve disorders, in which case it is usually termed cortical visual impairment (CVI).

The American Medical Association's Guides to the Evaluation of Permanent Impairment attempts to provide "a standardized, objective approach to evaluating medical impairments." The Visual System chapter "provides criteria for evaluating permanent impairment of the visual system as it affects an individual's ability to perform activities of daily living."[5] The Guide has estimated that the loss of one eye equals 25% impairment of the visual system and 24% impairment of the whole person;[5][6] total loss of vision in both eyes is considered to be 100% visual impairment and 85% impairment of the whole person.[5]

Visual impairments have considerable economic impact on even developed countries.[7] 'A major proportion of global visual impairment is preventable'.[8] An update based on census data of 2010 in the United States projects that 13 million Americans aged 40 and older will have a visual impairment or be blind by the year 2050.[9]

Classification[edit]

Anyone with reduced vision not corrected by spectacles or contact lenses is visually impaired. The World Health Organization uses the following classifications of visual impairment. When the vision in the better eye with best possible glasses correction is:

  • 20/30 to 20/60 : is considered mild vision loss, or near-normal vision
  • 20/70 to 20/160 : is considered moderate visual impairment, or moderate low vision

Legal blindness

  • 20/200 to 20/400 : is considered severe visual impairment, or severe low vision
  • 20/500 to 20/1,000 : is considered profound visual impairment, or profound low vision
  • More Than 20/1,000 : is considered near-total visual impairment, or near total blindness
  • No Light Perception : is considered total visual impairment, or total blindness

There are also levels of visual impairment based on visual field loss (loss of peripheral vision).

Go to visual acuity to consult an international visual acuity expression chart.

In the United States, any person with vision that cannot be corrected to better than 20/200 in the best eye, or who has 20 degrees (diameter) or less of visual field remaining, is considered legally blind or eligible for disability classification and possible inclusion in certain government sponsored programs.

United States[edit]

In the United States, the terms "partially sighted", "low vision", "legally blind" and "totally blind" are used by schools, colleges, and other educational institutions to describe students with visual impairments.[10] They are defined as follows:

  1. Partially sighted indicates some type of visual problem, with a need of person to receive special education in some cases;
  2. Low vision generally refers to a severe visual impairment, not necessarily limited to distance vision. Low vision applies to all individuals with sight who are unable to read the newspaper at a normal viewing distance, even with the aid of eyeglasses or contact lenses. They use a combination of vision and other senses to learn, although they may require adaptations in lighting or the size of print, and, sometimes, Braille;
    1. Myopic - unable to see distant objects clearly, commonly called near-sighted or short-sighted
    2. Hyperopic - unable to see close objects clearly, commonly called far-sighted or long-sighted
  3. Legally blind indicates that a person has less than 20/200 vision in the better eye after best correction (contact lenses or glasses), or a field of vision of less than 20 degrees in the better eye; and
  4. Totally blind students learn via Braille or other non-visual media.

Health effects[edit]

Visual impairments may take many forms and be of varying degrees. Visual acuity alone is not always a good predictor of the degree of problems a person may have. Someone with relatively good acuity (e.g., 20/40) can have difficulty with daily functioning, while someone with worse acuity (e.g., 20/200) may function reasonably well if their visual demands are not great.

Some people who fall into this category can use their considerable residual vision – their remaining sight – to complete daily tasks without relying on alternative methods. The role of a low vision specialist (optometrist or ophthalmologist) is to maximize the functional level of a patient's vision by optical or non-optical means. Primarily, this is by use of magnification in the form of telescopic systems for distance vision and optical or electronic magnification for near tasks.

People with significantly reduced acuity may benefit from training conducted by individuals trained in the provision of technical aids. Low vision rehabilitation professionals, some of whom are connected to an agency for the blind, can provide advice on lighting and contrast to maximize remaining vision. These professionals also have access to non-visual aids, and can instruct patients in their uses.

The subjects making the most use of rehabilitation instruments, who lived alone, and preserved their own mobility and occupation were the least depressed, with the lowest risk of suicide and the highest level of social integration.

Those with worsening sight and the prognosis of eventual blindness are at comparatively high risk of suicide and thus may be in need of supportive services. These observations advocate the establishment and extension of therapeutic and preventative programs to include patients with impending and current severe visual impairment who do not qualify for services for the blind. Ophthalmologists should be made aware of these potential consequences and incorporate a place for mental health professionals in their treatment of these types of patients, with a view to preventing the onset of depressive symptomatology, avoiding self-destructive behavior, and improving the quality of life of these patients. Such intervention should occur in the early stages of diagnosis, particularly as many studies have demonstrated how rapid acceptance of the serious visual handicap has led to a better, more productive compliance with rehabilitation programs. Moreover, psychological distress has been reported (and is exemplified by our psychological autopsy study) to be at its highest when sight loss is not complete, but the prognosis is unfavorable.10 Therefore, early intervention is imperative for enabling successful psychological adjustment.[11]

Cause[edit]

  • Albinism: is a congenital condition that can cause visual impairment as well as the lack of pigmentation in a person’s skin, hair and eyes. More specifically, the condition that characterizes most albino people with visual impairment or legal blindness is oculocutaneous albinism (OCA), which is triggered by the mutation of the tyrosinase gene (TYR) responsible for producing melanin pigment proteins.[12] OCA characteristics include 1) photosensitivity or photophobia (iris transillumination), 2) involuntary movement of the eye (nystagmus), 3) astigmatism (foveal hypoplasia), and 4) severe, but often functional, low acuity.[12]
  • Amblyopia: is a category of vision loss or visual impairment that is caused by factors unrelated to refractive errors or coexisting ocular diseases.[13] Amblyopia is the condition when a child’s visual systems fail to mature normally because the child either suffers from a premature birth, measles, congenital nubella syndrome, vitamin A deficiency, or meningitis.[14] If left untreated during childhood, amblyopia is currently incurable in adulthood because surgical treatment effectiveness changes as a child matures.[14] Consequently, amblyopia is the world’s leading cause of child monocular vision loss, which is the damage or loss of vision in one eye.[13] In the best case scenario, which is very rare, properly treated amblyopia patients can regain 20/40 acuity.[13]
  • Cataracts: is the congenital and pediatric pathology that describes the greying or opacity of the crystalline lens, which is most commonly caused by intrauterine infections, metabolic disorders, and genetically transmitted syndromes.[15] Cataracts are the leading cause of child and adult blindness that doubles in prevalence with every ten years after the age of 40.[16] Consequently, today cataracts are more common among adults than in children.[15] That is, people face higher chances of developing cataracts as they age. Nonetheless, cataracts tend to have a greater financial and emotional toll upon children as they must undergo expensive diagnosis, long term rehabilitation, and visual assistance.[17] Also, according to the Saudi Journal for Health Sciences, sometimes patients experience irreversible amblyopia[15] after pediatric cataract surgery because the cataracts prevented the normal maturation of vision prior to operation.[18] Despite the great progress in treatment, cataracts remain a global problem in both economically developed and developing countries.[19] At present, with the variant outcomes as well as the unequal access to cataract surgery, the best way to reduce the risk of developing cataracts is to avoid smoking and extensive exposer to sun light (i.e. UV-B rays).[20]
  • Corneal opacification
  • Degenerative myopia
  • Diabetic retinopathy: is one of the manifestation microvascular complications of diabetes, which is characterized by blindness or reduced acuity. That is, diabetic retinopathy describes the retinal and vitreous hemorrhages or retinal capillary blockage caused by the increase of A1C,[21] which a measurement of blood glucose or sugar level.[22] In fact, as A1C increases, people tend to be at greater risk of developing diabetic retinopathy than developing other microvascular complications associated with diabetes (e.g. chronic hyperglycemia, diabetic neuropathy, and diabetic nephropathy).[23] Despite the fact that only 8% of adults 40 years and older experience vision-threatening diabetic retinopathy (e.g. nonproliferative diabetic retinopathy or NPDR and proliferative diabetic retinopathy or PDR), this eye diseased accounted for 17% of cases of blindness in 2002.[24]
  • Glaucoma: also known as uveitic ocular hypertension[25] is a congenital and pediatric eye disease characterized with increased pressure within the eye or intraocular pressure (IOP).[26] Glaucoma causes visual field loss as well as severs the optic nerve.[27] Early diagnosis and treatment of glaucoma in patients is imperative because glaucoma is triggered by non-specific levels of IOP.[28] Also, another challenge in accurately diagnosing glaucoma is that the disease has four etiologies: 1) inflammatory ocular hypertension syndrome (IOHS); 2) severe uveitic angle closure; 3) corticosteroid-induced; and 4) a heterogonous mechanism associated with structural change and chronic inflammation.[29] In addition, often pediatric glaucoma differs greatly in etiology and management from the glaucoma developed by adults.[30] Currently, the best sign of pediatric glaucoma is an IOP of 21 mm Hg or greater present within a child.[31] One of the most common causes of pediatric glaucoma is cataract removal surgery, which lead to an incidence rate of about 12.2% among infants and 58.7% among 10 year olds.[32]
  • Macular degeneration
  • Retinitis pigmentosa
  • Retinopathy of prematurity: The most common cause of blindness in infants worldwide. In its most severe form, ROP causes retinal detachment, with attendant visual loss. Treatment is aimed mainly at prevention, via laser or Avastin therapy.
  • Stargardt's disease
  • Trachoma
  • Uveitis: is a group of 30 intraocular inflammatory diseases[33] caused by infections, systemic diseases, organ-specific autoimmune processes, cancer or trauma.[34] That is, uveitis refers to a complex category of ocular diseases that can cause blindness if either left untreated or improperly diagnosed.[35] The current challenge of accurately diagnosing uveitis is that often the cause or etiology of a specific ocular inflammation is either unknown or multi-layered.[33] Consequently, about 3-10% uveitis victims in developed countries, and about 25% of victims in the developing countries, become blind from incorrect diagnosis and from ineffectual prescription of drugs, antibiotics or steroids.[36] In addition, uveitis is a diverse category of eye diseases that are subdivided as granulomatous (or tumorous) or non-granulomatous anterior, intermediate, posterior or pan uveitis.[37] In other words, uveitis diseases tend to be classified by their anatomic location in the eye (e.g. uveal tract, retina, or lens), as well as can create complication that can cause cataracts, glaucoma, retinal damage, age-related macular degeneration or diabetic retinopathy.[38]

Epidemiology[edit]

  • Globally, in 2002 more than 161 million people were visually impaired, of whom 124 million people had low vision and 37 million were blind. However, refractive error as a cause of visual impairment was not included, which implies that the actual global magnitude of visual impairment is greater.
  • Worldwide for each blind person, an average of 3.4 people have low vision, with country and regional variation ranging from 2.4 to 5.5.[39]

Distribution of visual impairment[edit]

By age: Visual impairment is unequally distributed across age groups. More than 82% of all people who are blind are 50 years of age and older, although they represent only 19% of the world's population. Due to the expected number of years lived in blindness (blind years), childhood blindness remains a significant problem, with an estimated 1.4 million blind children below age 15.

By gender: Available studies consistently indicate that in every region of the world, and at all ages, females have a significantly higher risk of being visually impaired than males.

By geography: Visual impairment is not distributed uniformly throughout the world. More than 90% of the world's visually impaired live in developing countries.[39]

Since the estimates of the 1990s, new data based on the 2002 global population show a reduction in the number of people who are blind or visually impaired, and those who are blind from the effects of infectious diseases, but an increase in the number of people who are blind from conditions related to longer life spans.[39]

Diagnosis[edit]

Scientists track eye movements in glaucoma patients to check vision impairment while driving

It is critical that all people be examined by someone specializing in low vision care prior to other rehabilitation training to rule out potential medical or surgical correction for the problem and to establish a careful baseline refraction and prescription of both normal and low vision glasses and optical aids. Only a doctor is qualified to evaluate visual functioning of a compromised visual system effectively.[40]

Treatment[edit]

Aside from medical help, various sources provide information, rehabilitation, education, and work and social integration.

Information is fundamental. Doctors and sanitary personnel must have this information to offer the patient when the moment is right. The desolation that doctors experience when they must tell a patient they can't do anything more is only surpassed by the loneliness and isolation the patient, who does not know where to go or what to do for help. Administrative aids are valuable allies, though sometimes they may lie hidden under a legal mess. Adaptation to the disability and psychological help are priority-one issues and must be confronted from the start. Not least important and almost as urgent is the education of the patient and their family to confront the new situation. The adaptation of the work place (the one the person currently has or a different one) is regulated by laws and norms and there are interesting subventions for companies that make the necessary modifications to allow a person with disabilities into their work force; therefore the reluctance to hire visually handicapped people is an anti-economic prejudice, for the company and society. Lastly, social integration aids facilitate adapted leisure and cultural activities, and private and public initiatives tending to improve mobility and better access to information for everybody, including the visually impaired.

Optical aids[edit]

The vast majority of patients with low vision can be helped to function at a higher level with the use of low vision devices. Low vision specialists recommend appropriate low vision devices and counsel patients on how better to deal with their reduced vision in general. Many government and private organizations exist to aid the visually impaired.

In an article, Augusto Bruix Bayés[41] mentions that the main principle behind low vision is to magnify the image using various tools.

Improving far sight: works best with static objects

  • TV
  • Theater
  • Cinema
  • Contemplating scenery
  • Seeing the bus number

Improving near sight: the person must work closer to the object

  • Reading
  • Writing
  • Crafts

Improving sensitivity to contrast: the person must use special optical filters

Other tools:

  • Book stands
  • Special lights
  • Grid paper
  • Magnified games
  • Watches, audio thermometers, special phones, etc.

Efficacy of optical aids[edit]

In a study performed by this specialist on 1,000 patients, all subjects with a visual acuity above 0.02 decimal (20/1000 feet) significantly improved their vision. From this group, 48% were very satisfied with their visual aids, 44% were satisfied, 5% little satisfied and 3% unsatisfied. Adaptation process to visual aids In the patient's first visit, the most adequate options for their particular case are studied, taking into consideration their psychological, cultural, social and work factors, and the degree of improvement experienced with the selected aids, advising the patient on which aids improve quality of life. After the specific adaptation, there is a follow up to ensure the patient is correctly using and taking the best advantage of the visual aids. In some cases (approx. 4%), the initial visual aids must be changed. Once the patient is released, a report on their first visit and follow up is given to their eye doctor or the professional who made the referral. We believe that low vision, as a complementary technique to ophthalmology, has a great future, due to the progress of science, the increase of life expectancy, and the increasing need people have to access information.

Other aids[edit]

For the totally blind, there are books in braille, audio-books, and text-to-speech computer programs, machines and e-book readers. Low vision people can make use of these tools as well as large-print reading materials and e-book readers that provide large font sizes.

Computers are important tools of integration for the visually impaired person. They allow, using standard or specific programs, screen magnification and conversion of text into sound or touch (Braille line), and are useful for all levels of visual handicap. OCR scanners can, in conjunction with text-to-speech software, read the contents of books and documents aloud via computer. Vendors also build closed-circuit televisions that electronically magnify paper, and even change its contrast and color, for visually impaired users. For more information, consult Assistive technology.

In adults with low vision there is no conclusive evidence supporting one form of reading aid over another.[42] In several studies stand-based closed-circuit television and hand-held closed-circuit television allowed faster reading than optical aids.[42] While electronic aids may allow faster reading for individuals with low vision, portability, ease of use, and affordability must be considered for people.[42]

Children with low vision sometimes have reading delays, but do benefit from phonics-based beginning reading instruction methods. Engaging phonics instruction is multisensory, highly motivating, and hands-on. Typically students are first taught the most frequent sounds of the alphabet letters, especially the so-called short vowel sounds, then taught to blend sounds together with three-letter consonant-vowel-consonant words such as cat, red, sit, hot, sun. Hands-on (or kinesthetically appealing) VERY enlarged print materials such as those found in "The Big Collection of Phonics Flipbooks" by Lynn Gordon (Scholastic, 2010) are helpful for teaching word families and blending skills to beginning readers with low vision. Beginning reading instructional materials should focus primarily on the lower-case letters, not the capital letters (even though they are larger) because reading text requires familiarity (mostly) with lower-case letters. Phonics-based beginning reading should also be supplemented with phonemic awareness lessons, writing opportunities, and lots of read-alouds (literature read to children daily) to stimulate motivation, vocabulary development, concept development, and comprehension skill development. Many children with low vision can be successfully included in regular education environments. Parents may need to be vigilant to ensure that the school provides the teacher and students with appropriate low vision resources, for example technology in the classroom, classroom aide time, modified educational materials, and consultation assistance with low vision experts.

See also[edit]

References[edit]

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  3. ^ a b larrybelote.com
  4. ^ medem.com
  5. ^ a b c AMA Guides
  6. ^ Eye Trauma Epidemiology and Prevention
  7. ^ Taylor, HR; Pezzullo, ML; Keeffe, JE (2006). "The economic impact and cost of visual impairment in Australia". British journal of ophthalmology 90 (3): 272–5. doi:10.1136/bjo.2005.080986. PMC 1856946. PMID 16488942. 
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  10. ^ National Dissemination Center for Children with Disabilities
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  39. ^ a b c World Health Organization[full citation needed]
  40. ^ American Optometric Association web site
  41. ^ Baja Visión, 1999[full citation needed]
  42. ^ a b c Virgili G, Acosta R, Grover LL, Bentley SA, Giacomelli G (2013). "Reading aids for adults with low vision". Cochrane Database Syst Rev 10: CD003303. doi:10.1002/14651858.CD003303.pub3. PMID 24154864. 

External links[edit]