الفهرس 
The low visionOnly 14 pages are availabe for public view
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Abstract
Low vision or partial sighted is defined as reduced central acuity or visual
field loss even with the best optical correction provided by regular lenses.
Previously the person with low vision is the one who has impairment of
the visual functioning even after treatment and/or standard refractive correction,
and who has a visual field of less than 10 degrees from fixation point, but he
uses or is potentially able to use vision for planning or execution of task.
Later on the partial sighted patient known as a person who has visual acuity 3/60 to 6/60 with full visual field, or has visual acuity 6/24 or worse with moderate field constriction, or 6/18with gross field defect. While the blind patient known as person who has visual acuity 3/60 or worse, or has visual acuity 6/60 or worse with markedly restricted visual field.
The World Health Organization (WHO) definition of vision impairment in 2001 established in another way ,it considered blindness as VA worse than 20/400 in the better seeing eye (log MAR >1.30) and low vision as less than20/60 but better than or equal to 20/400 in the better seeing eye(log MAR 0.48 to , 1.30).
180 million people worldwide are visually impaired, with 50 million people bilaterally blind (less than 3/60 in the better Seeing Eye), 90% of the worlds blind live in the developing countries, 60% of which reside in sub-
Saharan Africa, China and India. Approximately 50%of worlds blind suffer
from cataract; other prevailing conditions include glaucoma, trachoma, onchocerciasis and number of childhood blindness diseases. If this definition is
expanded to include uncorrected refractive errors, the visually impaired patients
will become 259 million people worldwide.
American national centre for health statistics reported that visual impairments had the second highest rate and the largest increase in rate per thousand of population.
Patient of low vision are divided into 2 groups: A favorable group, and consists of those diseases that seem more amenable to improvement of visual acuity with special visual aids. This group includes: Albinism, macular degeneration, congenital nystagmus, degenerative myopia, and inoperable cases of cataract. Unfavorable group consists of that diseases that are less amenable to improvement and includes: retinitis pigmentosa, diabetic retinopathy, glaucoma
and optic atrophy.
Age-related macular degeneration is the leading cause of irreversible blindness in people 50 years of age or older in the developed world. More than 8 million Americans have age-related macular degeneration, and the overall prevalence of advanced agerelatedmacular degeneration is projected to increase by more than 50% by the year 2020.
Graphically the top 5 primary causes of unilateral and bilateral visual impairment (US definition) are, under corrected refractive error account for
about (51.9%), cataract(34.7%), Diabeticretinopathy (5.1%), age-relatedmacular
degeneration (3.8%), and glaucoma (2.9%).Other contributingcauses of visual impairment included posterior capsular opacification,macular holes, corneal scars, and amblyopic.
Proper assessment of different visual function is the keystone of successful vision rehabilitation strategy, this can be done through proper history taking and many objective tests as visual acuity both for far and near, color vision, contrast sensitivity, assessment of visual field, electrophysiology specially in young visual impaired children and evaluating mobility and navigation of patients.
Low vision aids are defined as devices that enhance the visual performance. They are optical aids that providing magnification as spectacles, microscopic lenses, hand , stand magnifiers and telescopic systems, or non optical aids as lighting, pinhole, pinhole glasses, typoscopes, reading and writing aids, filter lenses and aids for daily living in home and absorptive mobility. In addition the electronic vision enhancement systems , that rapidly advances and modified, its founded in several models as C.C.TV, Mouse-type EVES, Head-mounted EVES, Sonic aids, General positioning satellites (GPS), Blue-tooth technology and short-range wireless communication. Recently the intraocular LVAs as VIP IOL, prismatic IOL, mirror telescopic IOL and several forms of the retinal micro implants were used with the visual impaired patients.
Rehabilitation strategies of low vision patient are multidisciplinary approaches involving more than one service, ophthalmic, optometric, psychological, and educational and rehabilitation services.
The following items are the major headings of visual rehabilitation strategy:
- Identify the low vision patient.
- Assess the visual function.
- Evaluate the potential to use the residual vision.
- Proper prescription of optical or non optical LVAs evens the new surgical
procedure.
- Training and educate the patient on the methods of using visual aids and its
benefits.
- Environmental modification.
- Sensory substitution.
- Psychological rehabilitation.
- Orientation and Mobility training especially with field abnormalities.