Author : Dr Surabhi P M, MBBS, DOMS, DNB ,Senior Resident, Department of Ophthalmology, BGS Medical College & Hospital
The ability to see through eyes is vision. Ophthalmologists (eye doctors) test vision using various charts like Snellen’s chart, LogMAR chart, N chart for near vision etc.,
On Snellen’s chart a value of 6/6 indicates that a person’s distance vision is normal and a value of N6 on N chart means normal near vision.
As per the World Health Organization (2019), visual impairment is categorized as blindness when a person is unable to count fingers in daylight at a distance of 3 meters (<3/60).
Problems in different parts of the eye, the optic nerve or the brain can lead to blindness.
What is avoidable blindness?
1. Preventable blindness – this can be easily prevented by removing the cause at the right time.
Example: corneal blindness due to Vitamin A deficiency can be avoided if Vitamin A supplementation is provided at the appropriate time.
2. Curable blindness – here, lost vision can be restored by timely treatment.
Example: cataract surgery can be done to remove cataract, place an artificial lens in the eye and restore vision.
Common causes of blindness and their prevention:
1. Cataract: Most common cause of blindness and visual impairment in persons aged above 50 years. Cataract is the opacity of the natural lens of the eye which is usually old age related. In rare cases, cataract can occur in children and young adults. Surgery can help with the removal of cataract and placement of an artificial lens which can bring back the lost vision. Thus, it is vital to have regular visits to your eye doctor especially after the age of 50 years and get yourself checked for cataract.
2. Corneal opacity/ blindness: Cornea is a transparent layer without any blood vessels, which forms the entrance of the eye. It is responsible for allowing the right amount of light into the eye. If the cornea is diseased it can lose its transparency and blood vessels can grow into it, making it opaque. There are multiple causes for this and it can occur in all age groups. Corneal blindness can be present at birth due to congenital causes. Infections like trachoma and conjunctivitis can lead to corneal opacity. Trauma to cornea can cause corneal tears which may need surgical treatment. In those with poor immunity a trivial insult can lead to corneal ulcer due to which the whole eye can get affected and vision may be lost. However, in most cases if the nerve and retina of the eye are normal, it is possible to restore vision by corneal transplantation surgery.
3. Refractive Error: Most common and the most important cause of visual impairment children and adults aged less than 50 years. Here, refraction of light by the eye provides subnormal or blurred vision. Myopia (short-sightedness), Hyperopia (long-sightedness) and Astigmatism (cylindrical error) are the different types of refractive errors. If this error is left uncorrected or under corrected in children it can lead improper development and maturation of vision that can further cause permanent blindness. This condition is known as Amblyopia. Refractive errors can be corrected by spectacles or refractive surgeries. After 40 years of age, everyone will develop Presbyopia, which is, difficulty in near distance viewing. This can also be corrected by spectacles.
4. Glaucoma: This silent sight killer disease of the optic nerve can go unnoticed for several years before getting diagnosed at the advanced stage where the lost vision cannot be recovered. Glaucoma runs in families, but it can also affect any person randomly. People with Myopia and Hyperopia are at a higher risk of developing glaucoma. It has a variety of causative factors. Here the peripheral vision gets affected first and the central vision remains normal until the disease is in the advanced stage. Thus it is vital to observe if there is any difficulty in noticing vehicles on the sides while driving, if the spectacles have been changed multiple times in a year, any eye pain on and off, the presence of coloured haloes around a light source etc., Hence, yearly or half yearly eye checks are mandatory to everyone above the age of 40 years. Once diagnosed, glaucoma can be treated with eye drops or surgery, as deemed fit by the ophthalmologist.
5. Retinal causes of blindness: Retina is a layer of the inner part of the eye which consists of tens of thousands of nerve receptors to receive light and transfer it to the brain via optic nerve, where an image is created and sight is enabled. Retina can get damaged due to diabetes mellitus which may lead to bleeding inside the eye and loss of vision and this is known as diabetic retinopathy. It is mandatory for a diabetic to get regular eye checks half yearly or more frequently depending on the stage of diabetic retinopathy.
Age Related Macular Degeneration (ARMD) can significantly affect the lifestyle geriatric population. The earlier it gets diagnosed, the better is the prognosis.
6. Other causes: Eye injury (firecracker injury, ball injury, road traffic accident etc), cataract surgery complications, eye inflammation (uveitis), alcohol or nutrition related optic nerve weakness (optic neuropathy), eye related cancers (retinoblastoma, lid cancers) etc.
Conclusion:
Regular eye examinations by an Ophthalmologist is truly necessary for every child and adult. It can be both sight improving and sight saving.
Eye donation after the death of a person can gift vision to the blind.
Vision is a precious gift, save it. Visit your Ophthalmologist
