Vision loss that cannot be corrected with conventional glasses, contacts, or surgery is termed as low vision. It interferes with the daily performance of the individual, so a person with low vision must learn how to adjust to it. According to the latest global estimate, 36 million were blind, 216•6 million people had moderate to severe visual impairment, and 188•5 million had mild visual impairment. According to a recent survey, prevalence of visual impairment in Nepal was high among the age group 60 years and above. Refractive error being the major cause of low vision, followed by cataract and retinal disorders.
Eye conditions that can cause low vision are:
Macular degeneration is a disorder that affects the retina, the light-sensitive lining at the back of the eye where images are focused. The macula—the area on the retina responsible for sharp central vision—deteriorates, causing blurred vision. This can cause difficulty in reading, recognizing faces, driving, etc. The exact cause is unknown. Although age is the primary contributing factor, cigarette smoking and nutrition can also play a role in the development of age-related macular degeneration.
A cataract is a clouding of part or all the lens inside the eye. This clouding interferes with light reaching the retina at the back of the eye, resulting in a general loss of vision. Causes of cataract include aging, long-term exposure to the sun’s ultraviolet radiation, injury, disease, and inherited disorders. If the eye is healthy, a cataract can be surgically removed. Usually, an intraocular lens implant is inserted in the eye, and vision is restored. Cataract surgery has a high success rate in otherwise healthy eyes. However, cataract surgery is not always possible for people who also have other eye diseases. These people may require low-vision rehabilitation to maximize their remaining vision.
Glaucoma causes damage to the optic nerve. Most commonly, this occurs due to increasing internal pressure in the eye. It can also occur when the internal pressure of the eye does not increase, but there is not enough blood flow to the optic nerve. There are no early symptoms in the most common form of glaucoma, but the first signs of damage are defects in side (peripheral) vision and difficulty with night vision. If diagnosed early, it can be treated with drugs, or sometimes surgery can minimize vision loss.
People with diabetes can experience day-to-day changes in their vision, and/or visual functioning, because of the disease. Diabetes can cause blood vessels that nourish the retina to develop tiny, abnormal branches that leak. This can interfere with vision, and over time, may severely damage the retina. Laser procedures and surgical treatments can reduce its progression, but regulating blood sugar is the most important step in treating diabetic retinopathy.
Retinitis pigmentosa gradually destroys night vision, severely reduces side vision, and may result in total vision impairment. Its first symptom is night blindness, which usually occurs in childhood or adolescence.
In amblyopia, the visual system fails to develop normally during childhood. The blurry vision that results in one or both eyes is not easily corrected with normal glasses or contact lenses alone.
Retinopathy of prematurity (ROP)
Retinopathy of prematurity occurs in infants born prematurely. It is caused by the high oxygen levels in incubators during the critical neonatal period.
With a retinal detachment, the retina separates from its underlying layer. It can cause total vision impairment in the affected eye. Causes include holes in the retina, eye trauma, infection, blood vessel disturbance, or a tumor. If diagnosed early, most detached retinas can be surgically reattached, with vision partially or completely restored.
Acquired (traumatic) brain injury
Vision can also be lost or damaged as a result of head injuries, brain damage, and stroke. Signs and symptoms can include reduced visual acuity or visual field, contrast sensitivity, blurred vision, eye misalignment, poor judgment of depth, glare sensitivity, confusion when performing visual tasks, difficulty reading, double vision, headaches, dizziness, abnormal body posture, and balance problems.
Other eye conditions causing vision loss are: refractive errors, keratoconus, corneal scar, macular hole, optic atrophy, cerebral blindness in babies, retinoblastoma, etc. Vision loss can be overall blurred vision, central vision loss, and peripheral vision loss. There is difficulty in reading and writing, recognizing people, in orientation and mobility, finding way in dark, driving, making eye contacts, etc.
Careful observations can reveal vision loss. Tilting head indicates direction of visual field loss, increasing eye movement or head movement indicates advanced visual field loss. Wearing sunglasses indoor, maintenance of closed proximity around walls, reliance on tactile information by holding onto an individual also include vision loss. Appointment is necessary if you are noticing any of these changes in your close ones.
Each type of low vision problem requires a different therapeutic approach. Vision rehabilitation maximizes visual functioning, so the patient can achieve their visual goals and improve the quality of their life. Low vision therapists play a major role in management of visual impairment in rehab center to use the residual vision with optical devices, non-optical devices, and assistive technology. Low vision could be managed with the help of telescope mounted spectacle, bar magnifiers, hand magnifiers, loupes (high plus lenses), assistive technology (smartphones) and many more, which magnify the objects and help people with low vision to see those objects.
In the rehab center, low vision patients are provided with emotional support and encouragement. They are taught safe ways to move outdoors, indoors, and also in unfamiliar buildings. Training and information on daily living skills, such as cooking, cleaning, personal care, and usage of modified kitchen appliances, and adapted computer is provided to them. Information on availability of financial and other sources of help as per law is also provided. People with low vision can learn a variety of techniques to help them perform daily activities with their remaining vision. Government and private programs offer educational and vocational counseling, occupational therapy, rehabilitation training, and more.