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What is a colour vision test, and where can I take one in Goa?

Colour vision is on many forms in a port, Navy and airport town like Vasco: jobs at sea and in the port, electrical and wiring work, driving, the armed forces, airline and airport work, and some technical courses. It matters at home too. A child who mixes up colours at school may simply see colours differently, which is not a learning problem. This guide explains the test, what the result means and how to prepare. For all the eye tests done here, see eye check-ups at ReNew Vision.

What is colour blindness?

The retina, the light-sensitive layer at the back of the eye, has three kinds of cone cells, tuned to red, green and blue light. If one kind works differently or is missing, some colours look alike. Doctors call this colour vision deficiency. The everyday name is colour blindness, although very few people see no colour at all.

• Red-green deficiency is by far the most common type. Reds, greens, browns and oranges can look similar.
• Blue-yellow deficiency is much rarer.
• Complete colour blindness, seeing only shades of grey, is very rare and usually comes with poor vision from birth.

Who gets it?

Most colour vision deficiency is inherited and present from birth. The common red-green type is passed down on the X chromosome, so it is much more common in men: studies in India have found it in a few in every hundred men, and in far fewer women. A mother can carry it without being affected herself and pass it to a son.

Colour vision can also change later in life because of an eye or general health problem, such as cataract (the yellowing lens makes blues and whites look dull), glaucoma, diabetic eye disease, optic nerve problems or some medicines. A recent change in colour vision, or a change in one eye only, is a reason for a full eye check-up. Read about the early signs of cataract.

How is colour vision tested?

The usual test is a book of plates, each made of coloured dots. Hidden in the dots is a number or a winding line that people with normal colour vision see easily; people with a red-green deficiency see a different number, or none. It is often called the Ishihara test, after the doctor who designed it.

• The plates are shown in good light, at a comfortable reading distance.
• Wear your usual spectacles if you need them for reading. Tinted lenses and coloured contact lenses must come off.
• You get a few seconds for each plate. Just say what you see; there is no need to guess.
• Children who do not know numbers yet can trace the winding lines with a finger.

The plates are a screening test. They show whether a red-green deficiency is present, and roughly how strong it is. Some employers, especially in shipping, railways and aviation, use other tests as well, such as a lantern test, and some name their own approved examiners. If your form names a particular test or examiner, call 072489 88039 before you come so that we can tell you whether it can be done here.

Which jobs and forms ask for colour vision?

• driving licence medical forms; see eye fitness certificates
• port, shipping and shipyard jobs, where signal lights and colour codes matter
• the armed forces, police and fire services
• electricians, wiremen and electronics work, where wires are colour-coded
• airline and airport jobs
• some courses, such as technical trades, laboratory work, design and printing

The standard differs from job to job. A mild deficiency may not matter in one job but may rule out another. Before you apply, find out the standard for the job you want; an early test result helps you plan, rather than finding out at the final medical.

Can colour blindness be treated?

Inherited colour vision deficiency cannot be cured, and it does not get worse with age. Spectacles do not correct it. Tinted lenses sold for colour blindness can make some colours stand out more for some people, but they do not give normal colour vision, and they must not be worn during a colour vision test. When colour vision has changed because of an eye disease, such as cataract, treating the cause can help.

Colour vision in children

Children rarely know that they see colours differently; they assume everyone sees as they do. Signs include mixing up red and green crayons, trouble with colour-coded worksheets, charts or maps, or calling brown things green. If you notice this, an eye check-up can test colour vision along with the rest of the eyes. Knowing early helps teachers, and helps the child plan later study and work choices without a late surprise.

How to prepare for the test

• Bring the form, if you have one, and your spectacles or contact lenses.
• Do not wear tinted spectacles or coloured contact lenses to the test.
• Do not try to learn the plates from the internet. A result that does not match your real colour vision can put you and others at risk at work, and many examiners use more than one test.

When can I come for a colour vision test?

Colour vision tests are done in the Eye OPD at ReNew Vision, Vaddem, Vasco, Monday to Saturday, 4 pm to 7 pm. The plate test itself takes a few minutes; if you also need a full check-up or a certificate, allow more time. Call or WhatsApp 072489 88039, and see how to reach us.

Questions patients ask

How long does a colour vision test take?

The plate test takes a few minutes. If you also need a vision test, a spectacle power test or a fitness certificate, allow more time for the visit.

What is the Ishihara test?

A book of plates made of coloured dots, each hiding a number or a line. People with normal colour vision read them easily; people with a red-green deficiency see a different number or none. It is the usual screening test for colour vision.

Can colour blindness be cured?

Inherited colour blindness cannot be cured, but it does not get worse. Spectacles do not correct it, and tinted lenses do not give normal colour vision. If colour vision changes because of an eye disease such as cataract, treating the cause can help.

Is colour blindness more common in men?

Yes. The common red-green type is inherited on the X chromosome, so it affects far more men than women. A mother can carry it without being affected and pass it to a son.

Can I get a driving licence if I am colour blind?

A 2020 change to the medical forms allows people with mild to moderate colour blindness to apply for a driving licence. Severe colour vision loss can still matter. Check the current rules with your RTO.

Can a young child have a colour vision test?

Yes. Children who do not know numbers yet can trace the lines on the plates with a finger. Colour vision can be tested as part of a children's eye check-up.

This page is general eye-health information, not personal medical advice. Your eye doctor advises you after examining your eyes.