Vision, Hearing and Colour Perception: why these tests matter at sea
Vision, hearing and colour perception are essential parts of every medical examination.
Life and work at sea demand a high level of sensory awareness – seeing clearly, hearing accurately and responding quickly.
In this article, you’ll learn why these tests are so important, how they are performed, and what your results mean.
Sharp senses are essential
Safety at sea depends entirely on what you can see, hear and recognise.
From distinguishing navigation lights and light signals to reacting to alarms or radio calls – one moment of doubt can make the difference between safe operations and an accident.
The seafarer medical examination therefore checks whether your senses are sharp enough for your role on board.
The medical standards for seafarers are defined internationally in the STCW Code and the ILO/IMO Guidelines, ensuring the same level of safety across the global maritime industry.
Vision – seeing what’s happening
Good eyesight is essential at sea. You need to observe what happens around you – on the bridge, on deck or in the engine room – under bright sunlight, poor weather or at night.
During the medical, the doctor tests both distance and near vision, with and without glasses or contact lenses.
For bridge watchkeeping duties, each eye must reach a visual acuity of at least 0.5, and not less than 0.1 uncorrected. For engine room duties, the requirement is slightly lower: 0.4 per eye corrected, and 0.1 uncorrected.
The doctor also checks the visual field (at least 120 degrees) and screens for double vision or night blindness. Seafarers with one functional eye may still be considered fit, provided that the remaining eye has normal vision and the duties can be performed safely.
Vision at sea is more than sharpness – it’s about depth, contrast and awareness. Those few extra seconds of recognition can prevent an accident.
Hearing – staying alert to every sound
Sound is everywhere on a vessel: engines, ventilation, radio traffic, alarms.
Good hearing means recognising warnings and communication immediately, even in noisy conditions.
Hearing is tested with a pure tone audiometer, which measures how well you can hear different frequencies between 500 and 3000 Hz.
For safety-critical duties, your hearing must be good enough to understand normal speech at a distance of about three metres. For non-safety positions, the standard is slightly more lenient: speech should be clearly understood at two metres, with or without a hearing aid.
A hearing aid may be used, provided it can be worn safely on board.
Colour vision: safety at a glance
For bridge and engine room personnel, accurate colour perception is vital.
It ensures that navigation lights, signals and control indicators are identified correctly.
Testing begins with the Ishihara plates, where you read numbers or patterns made up of coloured dots.
If no errors occur, the test is passed immediately.
If the result is uncertain, further testing may follow – such as the HRR test, Lantern test, or Farnsworth D15.
At sea, misreading a light’s colour can mean the difference between passing safely and a collision. Bridge watchkeepers must meet the strictest CIE colour vision categories (1 or 2), while engineers must meet categories 1, 2 or 3.
Colour vision must be re-tested at least once every six years, and colour-correcting lenses or filters are not permitted.
If you don’t meet the standards
An abnormal result does not automatically mean you are unfit for work. The examining doctor always considers your specific duties on board and the practical and safety impact of the findings.
A mild hearing loss, for example, may be acceptable for engine room staff, while a navigation officer with colour deficiency cannot stand bridge watch.
If the condition does not pose a safety risk, the Maritime Medical Adviser (MAS) may grant an exemption, usually linked to specific duties and conditions, such as mandatory use of corrective aids.
In summary
Good sensory function is the foundation of safety at sea. Testing vision, hearing and colour perception ensures that every crew member can recognise risks and react quickly when needed.
These tests protect you, your colleagues and the vessel itself.
All seafarer medical examinations in the Netherlands fall under the supervision of the Human Environment and Transport Inspectorate (ILT).
Only doctors officially designated by the ILT are authorised to carry out these examinations.
At OmniHealth, all maritime medicals are conducted by ILT-approved doctors with extensive seafaring expertise – ensuring your certification fully meets international standards.
Written by Sven Daam, ILT-, OEUK- and ElementNL-certified medical examiner specialising in maritime and offshore health assessments.
Safeguarding fitness for work
In addition to this medical, OmniHealth also offers a range of other medical examinations
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