Thirty-two-year-old Aswathi (name changed) had been experiencing blurry vision in the right eye for two days. As she could not figure out the cause behind it, she consulted a doctor. When she was examined, her visual acuity (measured using an eye chart with letters and symbols) was 6/9, and her colour vision was abnormal. Pupil reaction (how the black centre of the eye changes size to control entry of light) test in the right eye showed abnormality while her fundus (back of the eye) was normal. “Through the examination, we found that she was suffering from optic neuritis of the right eye. The blurry vision, difficulty to identify red and green colours, was caused by the condition, and we promptly started treatment for optic neuritis,” says Dr Rehna Rasheed, assistant professor in ophthalmology at Amrita Hospital, Kochi.
Aswathi’s vision started improving in three days, and she slowly recovered almost completely. According to Dr Rehna, Aswathi’s acquired colour vision defect was one of the signs that aided in the diagnosis of optic neuritis. “Acquired colour vision deficiency is one of the symptoms/signs of many optic nerve and retinal diseases. The patients often come to us with other symptoms, such as blurry vision, a visual field defect, or a blind spot. Some of them also complain of colour vision difficulties,” adds Dr Rehna.
Colour vision defects can be caused by several reasons. When there are problems in the retina or the optic nerve, which connects the brain to the eye, there will be colour deficiency.
According to ‘A Global Perspective of Colour Vision Deficiency: Awareness, Diagnosis, and Lived Experiences,’ a study published in August 2025, acquired CVD can result from a wide range of factors, including ocular diseases; neurological diseases that affect the brain or optic pathways; medications and toxins, that is, certain drugs (hydroxychloroquine, ethambutol, antibiotics, and barbiturates) and exposure to industrial or environmental chemicals (carbon monoxide, carbon disulphide, and lead); trauma; and natural ageing processes, particularly after the age of 60.”
“Acquired causes of colour vision deficiency mainly pertain to retinal or macular diseases, like diabetes, or it could be optic nerve involvement. Glaucoma, optic neuropathy, toxins, and nutritional deficiencies such as Vitamin B12 and folic acid are other causes for acquired colour vision problems,” says Dr Sneha Giridhar, vitreoretinal consultant at Giridhar Eye Hospital, Kochi, adding that identification of the symptoms plays a crucial role.
Some medications can also cause colour vision problems. “There are two important medications that have a protocol for screening. Ethambutol, a medication used for the management of tuberculosis, and hydroxychloroquine, used for the treatment of rheumatology conditions can affect the optic nerve and retina respectively which can cause colour vision defect as an early sign. So the patients on these medications should undergo screening,” she said, adding that patients who experience blurry or colour vision problem require prompt clinical assessment and treatment.
“We recommend patients taking certain medications such as ethambutol and hydroxychloroquine undergo a baseline colour vision and ocular examination. A history of whether colour vision is affected can be tested each month before the patient collects the medication or annually based on the protocol,” highlights Dr Sneha, adding that the progression of the symptoms can be prevented if it is caught early.
Another aspect is ageing. Though ageing doesn’t cause colour blindness, changes in the lens, such as cataract, affect the transparency. “Yellowing and increasing density of the crystalline lens, and certain short-wavelength light not reaching the cones lead to a reduction in the differentiation of certain colours for the particular individual. Older people can even have age-related macular degeneration, where the photoreceptors get affected,” said Dr Sneha.
“For acquired deficiencies, depending on the underlying cause – for example, control of diabetes, glaucoma – and evaluation of optic neuropathies protect eye function and help in preventing further progression. Suspected medication toxicity requires prompt coordination between the prescribing physician and ophthalmologist,” she added.
Colour blindness
Colour blindness, or colour vision deficiency, is the decreased ability to tell the difference between shades. Several common colour deficiency diseases are genetic – they’re passed down from parents to their children. You can acquire colour vision deficiency later in life if you have a disease, injury that affects your eyes or brain, or due to certain medications
Genetic and Inherited Causes
X-linked mutations: Most color defects are congenital and inherited via the X chromosome Cone dysfunction: Abnormalities or missing photopigment genes affect the retina’s cone cells (red, green, or blue light sensors)
Gender bias: Men inherit the condition much more frequently than women because they have only one X chromosome
Acquired medical conditions
Eye diseases: Conditions like glaucoma, cataracts, and macular degeneration harm retinal tissue or optic nerves
Systemic illness: Chronic diseases such as diabetes, multiple sclerosis, Alzheimer’s, and Parkinson’s disease disrupt neural pathways responsible for visual processing
External and environmental factors
Medications: Certain drugs (such as hydroxychloroquine or specific heart and blood pressure treatments) have toxic side effects on vision
Chemical exposure: Toxins like carbon disulfide or specific fertilizers can damage the optic nerve
Natural aging: The eye’s lens yellows and retinal sensitivity naturally drops as a person grows older