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Low vision is a subspecialty within the professions of optometry and ophthalmology and opticianry dealing with individuals who have less than normal vision even with the most accurate conventional prescription available. It can be a result of either congenital or acquired factors. An example of the former is Leber's congenital amaurosis and of the latter age-related macular degeneration.
Classifying Low Vision
Anyone with noncorrectable reduced vision is considered to be visually impaired, and can have a wide range of causes. 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
- 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
- less 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 to be "legally blind" or eligible for disability classification and possible inclusion in certain government sponsored programs.
Magnitude of visual impairment
- 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.
Pathologies which may cause vision acuity loss
- Macular degeneration
- Corneal opacity
- Diabetic retinopathy
- Myopia magna
- Stargardt's disease
- Retinitis pigmentosa
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. This new information underscores the need to modify the health care agenda to include the management of the diseases that are now becoming prevalent.
Distribution of visual impairment
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. Geographically: Visual impairment is not distributed uniformly throughout the world. More than 90% of the world's visually impaired live in developing countries.
Low Vision, its lifestyle implications and rehabilitation
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. 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.
Once the emotional shock of the disability is overcome, if alternative techniques (basic rehabilitation) are learnt, good quality of life and an adjustment to the disability can be achieved, not only in the case of low vision, but also in the case of blindness.
According to an article published by The Academy of Psychosomatics Medicine, in a sample of patients affected by progressive diabetic retinopathy, only those who had reached total blindness actually displayed a decrease in psychic symptomatology, through learning rehabilitation techniques. More marked distress remained in the subjects with persisting partial sight. Unfulfilled expectations probably increased frustration at daily defeats, coupled with fear of complete loss of residual sight. Acceptance of one's pathology and final outcome is the basis for approaching and acquiring new behavioral patterns and creating good mental, physical, and social equilibrium in those who become blind.
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.
According to the Catalan Association for the Blind and Visually Impaired (ACCDV), experience tells that seeking the support of other people affected is a good therapy to overcome the disability, not only for the individual affected but for their families as well. There are associations that give this kind of support and can put the person in touch with professionals specialized in the collective's problems.
The Low Vision Examination
It is critical that all patients be examined by an optometrist or ophthalmologist 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 syetem effectively. American Optometric Association web site
Types of help available
The ACCDV states that medical help aside, the main ones are, in first place, information; secondly, what help the administration offers; and finally the ones which facilitate personal 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.
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 mentions that the main principle behind low vision is to magnify the image using various tools.
Improving Far sight: works best with static objects
- Contemplating scenery
- Seeing the bus number
Improving Near sight: the person must work closer to the object
Improving sensitivity to contrast: the person must use special optical filters
- Book stands
- Special lights
- Grid paper
- Magnified games
- Watches, audio thermometers, special phones, etc.
Effectivity of optical aids
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 will yield a better 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.
For the totally blind, there are books in braille, audio-books, machines and computer programs which transform text files into sound. Low vision people can, of course, make use of these tools as well.
Computers are, precisely, fundamental 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.
An ever-increasing number of people are at risk of visual impairment as populations grow and demographic shifts move towards the predominance of older age groups. Potentially blinding eye conditions such as age-related macular degeneration (AMD), diabetic retinopathy and glaucoma are increasing as the number of people affected grows. These are non-communicable chronic eye diseases to which the principles of long-term care including issues of cost of treatment and compliance (adherence) apply. Additionally, more programmes for those with low vision will need to be made available.
- World Health Organization
- de Leo et al: Blindness, Fear of Sight Loss, and Suicide,Psychosomatics 1999; 40:339–344
- Baja Visión, 1999
- American National Eye Institute Health Education Program
- Envision Choices and resources for people who are blind or low vision
- Journal of Visual Impairment & Blindness Special Issue on Low Vision
- National Eye Institute
- Lighthouse International Helping people with vision loss
- Low Vision Tips
- VisionAWARE - Self Help for Vision Loss Independence for adults with low vision
- Checkered Eye Project
- Catalan Association for the Blind and Visually Impaired
- Low Vision Tests - What is Low Vision?
- IALVS International Academy of Low Vision Specialists
- Vision Australia Vision Australia]
Eye disease - pathology of the eye (H00-H59, 360-379)
lacrimal system: Dacryoadenitis - Epiphora - Dacryocystitis
orbit: Exophthalmos - Enophthalmos
|Optic nerve and visual pathways||
Optic neuritis - Papilledema - Optic atrophy - Leber's hereditary optic neuropathy - Dominant optic atrophy - Optic disc drusen - Glaucoma - Toxic and nutritional optic neuropathy - Anterior ischemic optic neuropathy
accommodation and refraction
Paralytic strabismus: Ophthalmoparesis - Progressive external ophthalmoplegia - Palsy (III, IV, VI) - Kearns-Sayre syndrome
Other strabismus: Esotropia/Exotropia - Hypertropia - Heterophoria (Esophoria, Exophoria) - Brown's syndrome - Duane syndrome
|Visual disturbances and blindness||
Amblyopia - Leber's congenital amaurosis - Subjective (Asthenopia, Hemeralopia, Photophobia, Scintillating scotoma) - Diplopia - Scotoma - Anopsia (Binasal hemianopsia, Bitemporal hemianopsia, Homonymous hemianopsia, Quadrantanopia) - Color blindness (Achromatopsia, Dichromacy, Monochromacy) - Nyctalopia (Oguchi disease) - Blindness/Low vision
Trachoma - Onchocerciasis
See also congenital
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