Vision (Appendix A: ILO/IMO Guidelines)

Impairment and risks

  • In addition to the requirements for safely moving around a vessel many of the tasks of a seafarer require specified standards of visual performance.
  • Lookout duties need shape and colour discrimination, often in conditions of poor visibility both during the day and at night. These aspects of eye performance need to be combined with eye-brain co-ordination to support visual scanning capabilities and the ability to analyse the visual patterns seen.
  • The use of instrumentation and visual displays in all parts of a vessel similarly relies on adequate acuity and colour perception.
  • Denotative colour codes are used, especially in engineering, for cabling, gas cylinders and for visual warning and alarm systems.
  • Rapid changes of light intensity can occur and even where the seafarer has good dark adaptation, management arrangements need to allow time for adaptation to take place before reliance is placed on night-time visual observations.
  • Misperceptions and failures to interpret visual information correctly during bridge duties are common contributors to maritime incidents. Prior to the introduction of visual standards defects in acuity and colour perception also contributed. Incorrect judgements made about colour coding can also be safety critical.
  • Most visual defects are relatively stable and so individual capabilities can be tested. Some eye diseases are progressive, but change is generally over years rather than shorter periods. Defects in acuity (form perception) can usually be remedied by the use of spectacles or contact lenses. However in emergencies these aids may not be available and some minimum uncorrected vision is needed.
  • Loss of or poor vision in one eye has a minimal impairing effect in normal circumstances, but even minor problems with the single remaining eye will be incapacitating.


Rationale and justification

  • Good distant visual acuity has long been seen as essential for look-out duties. There are, however, no recent studies on the level of performance required and current standards worldwide have their origins in naval criteria set in the first half of the twentieth century. At this time it became feasible to accept vision corrected by spectacles as enclosed bridges prevented problems from spray.
  • Testing for acuity traditionally relies on high contrast static discrimination in the central visual area (fovea). There are no tests of dynamic discrimination, low contrast performance or response to objects first identified in the periphery that are practicable to apply to the routine assessment of seafarers.
  • Defects in the peripheral fields of vision or patchily across the whole visual field will give rise to blind spots. The brain normally fills in across such areas and so there may be loss of essential information that is needed to direct the gaze to objects of concern. The level of field loss that increases risk is unknown.
  • The Donders confrontation test of visual field is not reliable, except for detecting very large field defects. Several more reliable methods are available but all need dedicated equipment.
  • As the eye ages, its ability to respond to changing levels of illumination, to recover from glare and to accommodate to visual tasks at all distances deteriorates. The use of corrective lenses or spectacles can usually overcome accommodation limitations.
  • A few rare conditions lead to night blindness. In everyone, full dark adaptation takes at least ten minutes after coming from a well-lit area. This can result in failure to see dim objects or faint lights when starting night-time lookout duties. The use of tinted or photochromic lenses in spectacles can further impair dark adaptation. There is a detailed but dated research base on dark adaptation.
  • Defects in colour vision were found to be a cause of maritime accidents in the late nineteenth century. The commonest form of defect, found in around 5% of males but rare in females, is an inability to distinguish between red and green, the colours first adopted for oil navigation lights and still used. The defect is genetic and present throughout life. Very rarely a defect can develop secondary to another medical condition, or a minor level of impairment may become apparent as the eye ages.
  • Various tests for colour defects have been developed. Commonly Ishihara plates are used as an initial screen. Trade tests, for instance using coloured wires in electricians, do not give reliable results. For those doing lookout duties a lantern that simulates navigation lights in a dark room is the definitive test. For those who need to correctly recognise denotative colour codes there are several well-validated colour-matching tests.


Clinical Assessment and decision taking

Vision testing


All deck, engineering and radio department seafarers are required to meet the internationally agreed eyesight standards as specified in the medical and eyesight standards (STCW Table A-1/9, reproduced in Appendix A of ILO/IMO Guidelines).

A basic standard for unaided vision to ensure a degree of capability in emergency situations for all seafarers is also recommended in STCW Section B1.9, paragraph 10. This is because glasses may be missing or become damaged in such situations.

The standards are framed to provide maximum flexibility in their interpretation compatible with ensuring the health of the individual seafarer and maintaining the safety of ships at sea.

Both good visual acuity and unimpaired colour vision are essential for those undertaking lookout duties. This includes all deck officers and ratings. Lookout duties are those involving actually looking out to sea, (to check for hazards, other vessels etc) and should not be confused with 'watchkeeping' which is simply a nautical term for being on duty.

Engineering staff generally do not carry out lookout duties and are therefore required to meet somewhat less stringent eyesight standards. However, they will need to be capable of correctly recognising colour coding on cables, pipes and display screens.

In view of the serious consequences of not meeting the acuity and colour vision standards, anyone considering a seagoing career is strongly advised to have a full sight test/medical examination before beginning training to ensure that they meet the standards.

Catering and other passenger service staff are not required to meet specific acuity or colour vision standards, although they require adequate vision to undertake their duties efficiently and a basic level of unaided vision is recommended.

Since good vision is central to lookout duties and hence to ship safety, it is essential that vision testing is carried out to a high standard, which ensures consistent results. Discrepancies between repeat tests that result in restriction and consequential loss of work, for instance where previously undetected colour defects are found, can have a disastrous effect on a seafarer's career. It is therefore essential that conditions such as lighting balance and level are suitable for testing and that any delegation of the testing is to someone who is fully trained in procedures and aware of the need to be alert for any deception on the part of the person being examined. Test results brought by the seafarer should not be used as a substitute for testing at the examination. Borderline results should always be rechecked and all results fully recorded.

Any seafarer who requires visual aids to meet the aided acuity standard must use them when on watch and must have spare glasses or contact lenses with them on board at all times. Contact lens users should, in addition, have a pair of glasses to use in the event that soreness of their eyes prevents the wearing of contact lenses. They should also have the required cleaning fluids or a sufficient supply of disposable lenses to cover the full duration of their period at sea.

Photochromic lenses (those which darken with exposure to strong light and lighten in dark surroundings) have been shown significantly to reduce light transmission compared to uncoated lenses, which may reduce the likelihood of identifying navigation lights. Seafarers should be advised not to wear glasses with photochromic lenses or glasses that are permanently tinted when undertaking lookout duties at night.

Some medications can adversely affect vision. Where a person is taking such a medication long-term and their vision is safety critical a period of temporary unfitness while adapting to the medication and specialist assessment of the relevant aspects of visual function may be needed.


Examples include:

a) Acuity: hyoscine, atropine. (not non-absorbable products used as gastrointestinal antispasmodics')
b) Colour: chloroquine, sildenafil (transient yellow/green impairment only).
c) Dark adaptation: isoretinoin.
d) Visual fields: vigabatrin (unlikely at sea as used for seizure control)


Eyesight standards

Visual acuity (Table A-1/9)

The Snellen test type for distance vision should be used. Alternative well validated vision testing charts such as the 'LogMar' chart may be used but a Snellen chart should be retained and used for those who are very close to the standard. The test type should be either on an internally illuminated chart or externally illuminated either by daylight or by artificial illumination: lighting should be uniform and free from reflections. The test should be done at a measured distance (marked on the floor or wall) of six metres or at three metres if using half scale charts designed for this purpose. Vision in each eye should be tested separately, with observation to ensure that the unused eye is fully covered. Testing should be carried out without glasses or contact lenses and also with glasses/contact lenses if they are worn. 'Keystone' and similar desk based screeners are not an acceptable alternative.
Contact lenses will need to be removed for unaided visual acuity testing. Testing soon after removal can be inaccurate. Candidates should ideally wear glasses instead of lenses on the day of the examination, but bring their lenses to insert for corrected acuity testing. Where this is not possible, they should be aware that if their unaided acuity is borderline they will need to be re-tested either by the examining doctor or an optometrist.
For new entrants to officer cadetships, where restricted duties are impractical as the full range of training requirements has to be completed, those with visual acuity that does not meet the standards should be made permanently unfit. They should advised of the duties for which they could be suitable if they chose to apply for a cadetship in a different department. (see Keratoconus etc. below)


Colour vision (Table A-1/9)

(Note: IMO is making some small changes to Table A-1/9 and issuing a circular explaining them. This is because some of the confirmatory test methods recommended in the CIE report are no longer available.)

  • Initial Testing
    Medical examiners need to ensure that the seafarer meets the colour vision standards. Colour vision testing in serving seafarers need only be repeated every six years (STCW A-1/9 7(3.5)). This is because the impairment is almost always stable. The STCW requirements are based on those in the International Recommendations for Colour Vision Requirements in Transport (Commission Internationale de l'Eclairage CIE043-2001, including any subsequent versions). Testing for all seafarers should be done with the standard Ishihara plates or similar nationally approved pseudo-isochromatic plates. Some screen-based tests for colour vision are now available, however these are not among the currently recommended methods.
    Illumination should be either diffused daylight or from daylight spectrum fluorescent lighting. Incandescent lighting is unsuitable because of its colour balance. The criteria for a pass is three or less errors if, as recommended, the 38 plate test is used (two or less errors on the 24 plate test). It is essential that seafarers applying for certificates of competency as deck or dual career (merchant/fishing) officers have full colour vision.

    When testing a seafarer for the first time, special care must be exercised to ensure that the test is properly conducted. Such testing should not be delegated and the examining doctor should be aware that those with problems have been known, on occasions, to memorise the sequence of Ishihara plates. An inappropriate Ishihara test pass causes major problems for the seafarer and their employer if detected at a subsequent medical.
    Examiners should be aware that colour differentiating contact lenses are available but should never be used by candidates for colour vision tests as, while they may improve test results, they do not improve colour vision under maritime conditions. In practice, they are unlikely to ever be worn again if the test in successfully passed
    The Ishihara test is an effective screening test but will identify a few people with minor levels of colour vision impairment who are capable of performing duties at sea safely. Some maritime authorities have introduced supplementary testing for those who fail the Ishihara test. Where supplementary testing is performed the results of the supplementary test will determine any restrictions to be placed on the seafarer.
    At present the detailed requirements for supplementary testing vary between countries and national guidance should be followed. The recommendations of the CIE report (see above) should be referred to in cases of doubt.

  • Follow Up
    Most colour vision defects will be found in new seafarers and appropriate vocational advice should be given. Cases do occur where defects are detected in seafarers who previously apparently met the standards. It may be appropriate to recommend that the seafarer seeks optometric or ophthalmological advice in case there is any undetected eye disease or a requirement for improved correction of acuity, as the latter may impair performance at colour vision testing.

    A seafarer with colour vision defects working or potentially working in both deck and engine departments should be tested and restricted, if necessary, in relation to both. For new entrants to officer cadetships where restricted duties are impractical because the full range of training cannot be carried out those with defects should be made permanently unfit, but where appropriate advised of the duties for which they could be suitable if they chose to apply for a different cadetship.

  • Other personnel
    Seafarers with colour vision defects who carry out other duties on a ship eg catering, entertainment, hotel etc, where full colour vision is not required, should have their medical certificates restricted for their duties only.

  • Visual acuity and colour impairment test results
    The quantitative results rather than a statement of pass/fail should be recorded in the examination records. The seafarer's statutory certificate (STCW A-1/9 (3-4-3-7): should indicate whether unaided vision is adequate; whether visual acuity meets the standards; whether colour vision meets the standards and whether the seafarer is fit for lookout duties or has any restrictions placed on their duties because of visual (or other forms of impairment).

    In completing the certificate of fitness, clarity about any restrictions is important. The term 'lookout duties' should be used if acuity or colour vision do not meet the standards for deck duties rather than 'watchkeeping' as the latter term refers to the pattern of hours (watches) worked rather than to the use of the eyes.


Visual fields (Table A-1/9)

Clinical testing by confrontation (Donders test) should be undertaken. The seafarer should be referred to an optometrist for perimetry if there is any doubt about the completeness of fields, for instance because of a history of stroke or transient ischaemic attack, or if the seafarer draws attention to any visual problems. Any seafarer where there is a risk of diabetic retinopathy glaucoma requiring medication should also be referred or recent results obtained. Any defect other than a single small scotoma in the peripheral field will make the person unfit for lookout duties.


Night blindness (Table A-1/9)

There are no practicable tests for night blindness suitable for routine use in seafarers. Problems may become apparent in the course of the examination or conditions such as retinitis pigmentosa (see below) may be present. Functional impairment of night vision is more common in older seafarers, in particular the greater time taken to dark adapt at the start of a period of lookout duties or when exposed to higher levels of illumination as part of their night time bridge or ship patrolling responsibilities.


Diplopia, Squint and Monocular vision (Table A-1/9)

The revised STCW standards indicate that for all those performing deck, engineering and radio duties a specified level of effective binocular vision is required. This is in accord with existing requirements in some maritime states but in others it has been found possible to allow full or restricted duties to continue in the absence of full function in the less good eye, provided the best eye can carry out all required visual tasks fully and effectively and provided that, in the unlikely event of reduced function in the good eye for instance from injury or infection, there is another crew member aboard who is capable of taking over the person's duties.

Thus some authorities are likely to introduce transitional arrangements to enable such people to continue with their careers, while complying with the revised STCW standards for new entrants. This will be provided that:

  • there is full adaptation to the loss of function in one eye;
  • no individual safety related consequences are identified;
  • no confusing subsidiary images from diplopia are present;
  • and there is no risk of the impairing condition in the defective eye spreading to the functioning one.

An ophthalmological opinion on whether these criteria are met would normally be required.

In diplopia and squint, provided the image in the non-dominant eye is adequately suppressed to avoid visual confusion, it may be possible to perform some forms of work at sea. Where appropriate the same approach to that used for monocular vision may be applied for serving seafarers. If diplopia arises as the consequence of an accident then a period of restriction or temporary unfitness while vision becomes re-adapted may be needed.

Monocular vision may be a consequence of complete loss of vision in one eye, for instance from severe injury or enucleation, or be 'functional' for instance from a squint or from inability to achieve full refraction to meet the required standards in one eye. Monocular vision may be acceptable in a serving seafarer where national authorities allow this, but only where the functioning eye fully meets the standards required for the duties performed. However, it is not acceptable for any new seafarer starting their career or applying for the first time to work in the deck or engineering departments.

Monocular vision may be accepted in those newly entering the statutory medical examination system in the following situations.

  • Catering and customer service staff, as well as other groups not covered by STCW Table A-1/9.
  • Where allowed by current national seafarer fitness criteria.
    • those with sea service in the fishing sector transferring to work in the merchant navy, where they are formally new merchant seafarers despite their past experience.
    • yachtmasters who gain commercial endorsements and thus become new entrants to the statutory medical examination system. This group should never be suitable for lookout duties if to be the sole competent crew member on a commercial yacht but may be considered fit if there will always be other crew members fully competent to take over their duties on board.

Employer responsibility – The employer may have a "special duty of care" to ensure that the one good eye in a monocular seafarer is not put at risk of injury. This may be expressed, for instance, by a restriction (as appropriate) on work with strong alkalies, or with power tools that create fast-flying debris. Continuous use of protective eyewear is an alternative approach. Seafarers or their employers, depending on the relationship of the examining doctor to the employer, should be advised of the need to adopt special precautions.


Laser refractive surgery (Additional Guidance appendix 1 or ILO/IMO Guidelines)

Whilst it is acknowledged that laser refractive surgery can significantly improve visual acuity, it is not recommended that examining doctors support or endorse this treatment as a means of meeting visual standards for work at sea in view of potential adverse consequences of complications arising during or after treatment. If a seafarer decides to undertake the procedure and returns for reassessment, it is recommended that they are made temporarily unfit for lookout duties for 6 months after surgery and then assessed by an ophthalmologist, looking in particular at the subjective quality of vision, contrast and glare sensitivity and night vision. On retesting, they can be issued with a short term unrestricted certificate until stability is confirmed.

Where a seafarer has undergone other novel treatment for eye disease such as insertion of aphakic lenses or the use of orthokeratotic devices, or asks advice on the effect of such treatment on their fitness for seafaring, the basis for determining fitness should remain current performance and the best estimate of its stability until the next medical.


Eye Diseases (ILO/IMO Guidelines Appendix E H00-59)

Testing of current visual function is the main basis for determining visual fitness. However certain diseases may either result in types of vision defect that will not be apparent on the routine tests used or will, because of their progressive or recurrent nature, mean that frequent surveillance is needed in serving seafarers or that a career at sea is not advisable because it is likely to come to a premature end as a result of deteriorating vision.

  • Cataract
    Most commonly in older seafarers. Reduced acuity and problems with glare. Obtain opthalmological opinion on rate of progression and decide if time limited certificate is needed. Where cataract is unilateral with confirmed absence of change in the other eye a serving seafarer may be considered to be functionally monocular (see above). If, unusually, they meet acuity standards then a specialist assessment of interference with vision from glare is needed. Where surgery has been performed intraocular replacement lenses are not a barrier to employment, provided the vision standards are met and there is confirmation from an ophthalmologist that there is no other eye disease or visual impairment present.

  • Glaucoma
    Most commonly in older seafarers. Reduced field of vision, reduced acuity and patchy visual field losses (scotomata) in central area of vision. If, unusually, they meet acuity standards then an ophthalmological report on visual fields, scotomata and expected rate of progression is needed. Regular eye medication is usually prescribed. Check that there are no side effects or visual impairment from its use and that sufficient is carried to cover period at sea. Issue a time limited certificate if progression likely within next two years.

    Following acute glaucoma with recovery a period is needed to confirm stabilisation and then decisions should be based on an opthalmologist's report about the likelihood of recurrence, the adequacy of treatment, any risks to the other eye and the whether any continuing surveillance is indicated.

  • Diabetic eye disease
    Most of those with this condition have clinically diagnosed diabetes and so will have limitations on work at sea. It is characterised by patchy visual loss (scotomata) at random across the visual fields. Acuity standards will often not be met, but if a diagnosis of diabetic retinopathy has been made and they are met, a specialist report on likely progression should be obtained to determine the duration of certificate given. Limitation of work to near coastal waters may be needed in case of an exacerbation of the retinopathy or of the underlying diabetes (see 12).

  • Macular degeneration
    This is mainly a condition of older seafarers. As central vision is lost it will not normally be possible to meet the requirements for visual acuity.

  • Keratoconus and other progressive causes of reducing visual acuity in new recruits
    For keratoconus the pace of progression may be slowed by special corneal lenses. Such conditions are likely to progress to the stage where vision standards are not met by middle age. If diagnosed in new entrant they should be advised of the risk of a shortened career. If they currently meet the visual standards and an ophthalmological report indicates that they are likely to continue to do so for several years they should be considered fit but have their vision tested annually and be issued with a time limited certificate.

  • Recurrent eye infection or inflammation e.g. corneal ulcers, uveitis.
    These conditions may cause transient impairment of vision. A specialist report indicating likelihood of a recurrence and the scope for prevention of impairment by prophylaxis or by early treatment should re-infection arise should be the basis for decision taking.

  • Acute conditions impairing vision
    Retinal detachment and retinal haemorrhage can lead to sudden loss of unilateral vision, followed by recovery that may be complete or partial. Compliance with the standards in Table A-1/9 is the first requirement. If these can be met a specialist view on the likelihood of recurrence or of progression should be obtained and used as the basis for deciding on certification. Any underlying diseases responsible for these conditions will also have to be considered.

  • Conditions of the eyelids, blepharospasm and recurrent infections
    Severe blepharospasm may reduce effective visual function and lead to rapid visual fatigue. A specialist opinion on the scope for treatment and prognosis should be obtained and if the person can meet the visual standards with or without treatment then they should be considered fit. Infections of the eyelids will not threaten vision but can be temporarily disabling. If there is a history of recurrent blepharitis or other lid infections then the condition should be investigated and definitively treated before the person is considered fit for unlimited duties.

  • Retinitis pigmentosa
    This genetic condition results in loss of night vision and reduced visual fields. The rate of progression is variable. The condition is likely to limit the fitness of the sufferer, particularly in relation to navigational watchkeeping duties. A specialist opinion should be obtained, to include assessments of low light acuity and visual fields, and the vision testing results and the specialist opinion should then be used to decide on fitness category.

  • Neurological disease and head injury affecting visual function
    Conditions including multiple sclerosis, stroke, tumours and severe head injury can cause damage to the processing of visual information in the brain. Some of these changes can be subtle and are not detectable by the normal vision tests used. If a person has a history or any significant neurological disease or head injury a detailed report on their visual function should be obtained from the specialist who treated them and this, together with the results of vision tests should be used to decide on fitness category and the duration of any certificate issued.