Colour vision disturbance

Colour vision disturbance is difficulty distinguishing colours, or a change in colour appearance. It may be congenital (common, usually red green) or acquired (optic nerve, retinal, drug, systemic).

Physiology. Three cone types (long, medium and short wavelength) allow colour discrimination. Congenital red green deficiency affects about 8 percent of males and 0.5 percent of females (X linked). Blue yellow deficiency is rare and usually acquired. Acquired disturbance typically affects colour saturation and red green discrimination in optic nerve disease.

Classification. Congenital (protan, deutan, tritan; anomalous trichromacy; dichromacy; achromatopsia and blue cone monochromacy) and acquired (optic neuropathy, macular and cone disease, media opacity, drugs and toxins, cerebral achromatopsia).

Key distinctions. A lifelong, bilateral, symmetrical, stable deficit with normal acuity points to congenital disease. Colour desaturation in one eye with a relative afferent pupillary defect and pain on movement indicates optic neuritis. A blue yellow defect points to retinal, glaucomatous or toxic disease.

History. Age of onset, lifelong or new, unilateral or bilateral, colours affected, colours looking washed out (red desaturation), reduced vision, pain on eye movement, headache, other visual symptoms (field loss, photophobia), family history (affected males, maternal uncles), occupation (colour critical work), smoking, alcohol, nutritional status, diabetes, previous eye or brain disease, trauma, drugs, and exposure to solvents or heavy metals.

Drug history. Ethambutol, isoniazid, linezolid, amiodarone, digoxin (yellow vision), sildenafil and other phosphodiesterase inhibitors (blue tinge), hydroxychloroquine, chloroquine, vigabatrin, ethanol, methanol, tobacco, chemotherapy (oxaliplatin), phenothiazines, and quinine.

Examination. Visual acuity, colour vision tests (Ishihara pseudoisochromatic plates for red green; Hardy Rand Rittler plates; Farnsworth D15 and Farnsworth Munsell 100 hue tests; Nagel anomaloscope for definitive classification; red desaturation test), pupils (relative afferent defect), visual fields, eye movements, slit lamp (lens colour change, cataract), dilated fundus (macula, disc pallor, drusen, retinal disease), intraocular pressure, and neurological examination.

Red flags

• Acquired and new colour change, especially unilateral
• Reduced vision, relative afferent pupillary defect or disc swelling or pallor
• Pain on eye movement (optic neuritis)
• Field defect, headache or neurological signs (compressive lesion, stroke)
• Ethambutol, linezolid or amiodarone use
• Alcohol or tobacco excess with malnutrition (nutritional optic neuropathy)
• Child with photophobia, nystagmus and poor vision (achromatopsia)
• Sudden onset (vascular or demyelinating disease)

Special groups. Children: congenital deficiency affects school and career choice; screen boys at school entry where practical. Pregnancy: no specific issues. Older adults: cataract (blue deficiency), macular degeneration, glaucoma, drug toxicity. Region specific: tropical and nutritional optic neuropathies, methanol poisoning, and tuberculosis treatment toxicity.

Congenital

• Red green deficiency (protanopia, protanomaly, deuteranopia, deuteranomaly), tritan defects
• Achromatopsia (rod monochromacy), blue cone monochromacy, cone dystrophy and cone rod dystrophy, Leber congenital amaurosis, albinism

Acquired, optic nerve

• Optic neuritis, ischaemic optic neuropathy, compressive optic neuropathy, glaucoma, papilloedema, traumatic optic neuropathy
• Toxic and nutritional optic neuropathy (ethambutol, linezolid, amiodarone, methanol, tobacco alcohol amblyopia, vitamin B12 deficiency, folate deficiency)
• Hereditary optic neuropathy (dominant optic atrophy, Leber hereditary optic neuropathy)

Acquired, retinal and media

• Age related macular degeneration, diabetic retinopathy and maculopathy, central serous chorioretinopathy, retinal vein occlusion, retinitis pigmentosa, Stargardt disease, toxic maculopathy (hydroxychloroquine)
• Cataract and lens yellowing, aphakia, vitreous haemorrhage, corneal disease

Cerebral and other

• Cerebral achromatopsia (occipitotemporal lesion), stroke, tumour, migraine, posterior cortical atrophy
• Drug and toxin induced, hepatic and renal disease, hyperglycaemia, lead and mercury toxicity, solvents, and functional

Reasoning. Decide whether colour loss is lifelong or acquired. If acquired, test acuity, fields, pupils and fundi, and image the visual pathway when optic nerve disease is suspected.

First line. Colour plates (Ishihara), visual acuity, pupils, fields, fundoscopy and drug history.

Targeted tests.

• Farnsworth D15 or Farnsworth Munsell 100 hue test, anomaloscope, or computerised colour tests for classification.
• Optical coherence tomography of macula and retinal nerve fibre layer, automated perimetry, and fundus photography.
• Electroretinogram (cone function) and genetic testing for suspected cone disorders.
• MRI brain and orbits with gadolinium for optic neuritis, compressive lesions and cerebral achromatopsia; aquaporin-4 and MOG antibodies in atypical optic neuritis.
• Blood tests: glucose and HbA1c, vitamin B12, folate, thiamine, full blood count, ESR and C reactive protein (giant cell arteritis), syphilis serology, thyroid function, liver and renal function, lead and heavy metal levels, and methanol level and acid base status in suspected poisoning.
• Genetic testing for Leber hereditary optic neuropathy mitochondrial mutations.

Limitations. Screening plates do not classify severity or type of deficiency. Colour tests are affected by lighting and visual acuity.

Congenital colour deficiency. No treatment. Counselling, education about occupational restrictions (aviation, rail, electrical, military and some medical or design roles), use of colour labelling and coding, and aids (smartphone colour identification applications, filter lenses that enhance contrast; they do not restore normal colour perception). Inform schools and employers appropriately. Genetic counselling for families.

Optic neuritis. Methylprednisolone 1 g IV daily for 3 to 5 days under neurology and ophthalmology care (hastens recovery; final visual outcome is unchanged); MRI brain; plasma exchange for severe loss unresponsive to steroids; do not use low dose oral prednisolone alone (increased recurrence).

Giant cell arteritis. Prednisolone 40 to 60 mg orally each morning started before biopsy, with aspirin 75 mg daily and bone protection; methylprednisolone 500 mg to 1 g IV daily for 3 days with visual symptoms; same day specialist review.

Toxic optic neuropathy. Stop or substitute the culprit drug after urgent discussion with the prescriber (ethambutol: stop immediately; linezolid and amiodarone: review risk and benefit), check visual acuity and colour vision monthly during ethambutol therapy (and baseline before starting), and avoid alcohol and tobacco.

Nutritional optic neuropathy. Hydroxocobalamin 1 mg IM on alternate days until no further improvement (up to 3 weeks), then 1 mg every 2 months; folic acid 5 mg orally daily only after B12 replacement has started; thiamine 100 mg orally three times daily (500 mg IV every 8 hours for 3 days when Wernicke encephalopathy is possible); balanced diet; stop alcohol and tobacco.

Methanol poisoning (emergency). Fomepizole 15 mg/kg IV loading dose then 10 mg/kg every 12 hours for 4 doses (15 mg/kg every 12 hours thereafter), folinic acid 50 mg IV every 6 hours, bicarbonate for acidosis, and haemodialysis by toxicology and nephrology; ethanol infusion when fomepizole is unavailable.

Compressive lesions. Neurosurgical, endocrine and oncology care (hydrocortisone 100 mg IV then 50 mg every 6 hours for pituitary apoplexy; cabergoline 0.25 mg orally twice weekly for prolactinoma).

Macular and retinal disease. Treat the cause: neovascular macular degeneration and diabetic macular oedema (intravitreal anti-vascular endothelial growth factor injections: aflibercept 2 mg, ranibizumab 0.5 mg, bevacizumab 1.25 mg, or faricimab 6 mg, monthly for 3 doses then by response), central serous chorioretinopathy (observation, stop steroids, photodynamic therapy), and glaucoma (latanoprost 0.005 percent 1 drop at night or timolol 0.5 percent 1 drop twice daily).

Cataract. Surgical removal when visual function is affected; colour perception often improves after lens replacement.

Leber hereditary optic neuropathy. Genetic counselling, avoidance of smoking and excess alcohol, idebenone 900 mg orally daily in three doses with food (specialist), and low vision support.

Cerebral achromatopsia. Treat the cause (stroke prevention and care: aspirin 300 mg then clopidogrel or aspirin 75 mg daily, atorvastatin 80 mg at night, blood pressure under 130/80 mmHg), rehabilitation, and neurology care.

Monitoring. Visual acuity and colour vision every 1 to 3 months during ethambutol and other toxic drugs; repeat colour plates at each review of optic nerve disease; optical coherence tomography and fields for glaucoma.

Referral and escalation. Same day ophthalmology for acquired unilateral colour loss with visual loss or pain. Neurology for optic neuritis and cerebral causes. Genetics for inherited disease. Occupational health for colour critical work.

Admission criteria. Methanol poisoning, giant cell arteritis with visual loss, pituitary apoplexy, stroke, or rapidly progressive optic neuropathy.

Discharge and safety netting. Return for new visual loss, pain on eye movement, field loss, headache, double vision, or worsening colour perception while taking ethambutol or similar drugs.