What is Low Vision?
People with low vision have reduced vision, even when using the best possible corrective lenses. Low vision may be a result of either congenital disease such as retinite pigmentosa, albinism, cataract, diabetic retinophaty, glaucoma, macula degeneration, retinitis pigmentosa and so on or of an acquired conditions such as optic atrophy. It is treated within a subspeciality of optometry and ophthalmology called “low vision”. 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).
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.
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. If alternative techniques (basic rehabilitation) are learnt, good quality of life and an adjustment to the disability can be achieved. 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.
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.
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 incrising as the number of people affected grows.
The main principle behind low vision is to magnify the image using various tools. mage using various tools..
Improving far sight: Improving far sight:
• Contemplating scenery
• Seeing the bus number
For these tasks, galilaian and keplerian systems are suggested (LEGIT GALILEO and LEGIT KEPLERO)
Improving near sight: Improving near sight:
For these tasks, prismatic glasses, hyper corrective glasses and aplanatic systems or/and CCTV are the best solution (LEGIT BINO, LEGIT APLANAT, LEGIT MONO) Improving sensitivity to contrast: the person must use spe Improving sensitivity to contrast: cial optical filters (LEGIT SKUDO medical filters such as 450/511 nm)
Betterize visual comfort. Blue light filters can absorb Betterize visual comfort. short wavelength, high-energy light, which causes discomfort to light-sensitive eyes and reduces contrast. Low vision people (often photophobic,) may use special optical filters (LEGIT SKUDO medical filters such as: MD/400450/511/527/550/585/600 nm in standard version if used indoor or polarized/photochromic version if used outdoor).
Low Vision Causes:
Macular degeneration, often age-related macular degeneration (AMD or ARMD), is a medical condition that usually affects older adults and results in a loss of vision in the center of the visual field (the macula) because of damage to the retina. It occurs in “dry” and “wet” forms. It is a major cause of blindness and visual impairment in older adults (>50 years). Macular degeneration can make it difficult or impossible to read or recognize faces, although enough peripheral vision remains to allow other activities of daily life. Although some macular dystrophies affecting younger individuals are sometimes referred to as macular degeneration, the term generally refers to age-related macular degeneration (AMD or ARMD).
Macular degeneration by itself will not lead to total blindness. For that matter, only a very small number of people with visual impairment are totally blind. In almost all cases, some vision remains. The loss of central vision profoundly affects visual functioning. It is quite difficult, for example, to read without central vision. Pictures that attempt to depict the central visual loss of macular degeneration with a black spot do not really do justice to the devastating nature of the visual loss.
This can be demonstrated by printing letters six inches high on a piece of paper and attempting to identify them while looking straight ahead and holding the paper slightly to the side. Most people find this difficult to do. There is a loss of contrast sensitivity, so that contours, shadows, and color vision are less vivid.
Diabetic retinopathy, is retinipathy (damage to the retina) caused by complications of diabetes, which can eventually lead to blindness. It is an ocular manifestation of diabetes, a systemic disease, which affects up to 80 percent of all patients who have had diabetes for 10 years or more. Despite these intimidating statistics, research indicates that at least 90% of these new cases could be reduced if there was proper and vigilant treatment and monitoring of the eyes. The longer a person has diabetes, the higher his or her chances of developing diabetic retinopathy. 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, which a measurement of blood glucose or sugar level. 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). Despite the fact that only 8% of adults 40 years and older experience vision-threatening diabetic retinopathy, this eye diseased accounted for 17% of cases of blindness in 2002.
Retinitis pigmentosa (RP) is an inherited, degenerative eye disease that causes severe vision impairment and often blindness. The progress of RP is not consistent. Some people will exhibit symptoms from infancy, others may not notice symptoms until later in life. Generally, the later the onset, the more rapid is the deterioration in sight. Those who do not have RP have 90 degree peripheral vision, while some people who have RP have less than 90 degrees.
A form of retinal, RP is caused by abnormalities of the (rods and cones) or the retinal pigment epithelium (RPE) of the retina leading to progressive sight loss. Affected individuals may experience defective light to dark, dark to light adaptation or nyctalopia (night blindness), as the result of the degeneration of the peripheral visual field (known as tunnel vision). Sometimes, central vision is lost first causing the person to look sidelong at objects.
The effect of RP is best illustrated by comparison to a television or computer screen. The pixels of light that form the image on the screen equate to the millions of light receptors on the retina of the eye. The fewer pixels on a screen, the less distinct will be the images it will display. Fewer than 10 percent of the light receptors in the eye receive the colored, high intensity light seen in bright light or daylight conditions. These receptors are located in the center of the circular retina. The remaining 90 percent of light receptors receive gray-scale, low intensity light used for low light and night vision and are located around the periphery of the retina. RP destroys light receptors from the outside inward, from the center outward, or in sporadic patches with a corresponding reduction in the efficiency of the eye to detect light. This degeneration is progressive and has no known cure as of January 2014.
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. 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.
Some of the visual problems associated with albinism arise from a poorly developed retinal pigment epithelium (RPE) due to the lack of melanin. This degenerate RPE causes foveal hypoplasia (a failure in the development of normal foveae), which results in eccentric fixation and lower visual acuity, and often a minor level of strabismus.
The iris is a sphicter formed from pigmented tissue that contracts when the eye is exposed to bright light, to protect the retina by limiting the amount of light passing through the pupil. In low light conditions the iris relaxes to allow more light to enter the eye. In albinistic subjects, the iris does not have enough pigment to block the light, thus the decrease in pupil diameter is only partially successful in reducing the amount of light entering the eye. Additionally, the improper development of the RPE, which in normal eyes absorbs most of the reflected sunlight, further increases glare due to light scattering within the eye. The resulting sensitivity (photophobia) generally leads to discomfort in bright light, but this can be reduced by the use of sunglasses and/or brimmed hats.
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. Cataracts are the leading cause of child and adult blindness that doubles in prevalence with every ten years after the age of 40. Consequently, today cataracts are more common among adults than in children. 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.
Also, according to the Saudi Journal for Health Sciences, sometimes patients experience irreversible amblyopia after pediatric cataract surgery because the cataracts prevented the normal maturation of vision prior to operation. Despite the great progress in treatment, cataracts remain a global problem in both economically developed and developing countries. 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).
OPTICAL NERVE ATROPHY
The optic nerve contains axons of nerve cells that emerge from the retina, leave the eye at the optic disc, and go to the visual cortex where input from the eye is processed into vision. There are 1.2 million optic nerve fibers that derive from the retinal ganglion cells of the inner retina. neuropathy refers to damage to the optic nerve due to any cause. Damage and death of these nerve cells, or neurons, leads to characteristic features of optic neuropathy. The main symptom is loss of vision, with colors appearing subtly washed out in the affected eye. On medical examination, the optic nerve head can be visualised by an ophthalmoscope. A pale disc is characteristic of long- standing optic neuropathy. In many cases, only one eye is affected and patients may not be aware of the loss of color vision until the doctor asks them to cover the healthy eye.
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