ON a ski mountain in Switzerland last December, I saw a poster advising the public to give way to blind skiers. It reminded me of how willpower and senses other than sight can overcome the handicap of vision loss.

However, although vision may not be an absolute requisite for skiing, some activities and jobs require excellent vision, without a doubt. This knowledge is important for the safety of society and for career counselling.

The military.

Countries have different visual requirements for enlistment into various military categories.

For select groups like air force, navy (especially divers) and commandos, excellent vision in each eye, normal colour vision, good depth perception and no other eye deficiencies are the usual requirements.

The limits of acceptable refractive errors are often also defined. In Singapore, to qualify for the special groups, allowable refractive errors are capped at 500 degrees myopia and 200 degrees astigmatism.

Due to the rough and critical situations in the military, a common trend in the last decade - in a bid to improve readiness in increasingly myopic populations - is relaxation for laser refractive surgeries to correct refractive errors, such as the age-old photorefractive keratectomy (PRK), with a longer downtime, and the short downtime laser in-situ keratomileusis (Lasik).

In many countries, army personnel are allowed to undergo (or to have undergone) laser eye surgeries to improve their vision. This is in recognition of the long-term safety, efficacy and positive results of these surgeries.

In Singapore, as far as I know, PRK is the only currently approved surgery for the select military sub-groups, while the United States allows PRK, and in more recent years, wavefront-guided Lasik and implantable contact lens, too.

The most recent laser technique, small-incision lenticule extraction (SMILE), is being offered as a trial by the US army currently.

Airline pilot.

For commercial pilots, excellent eyesight is a prerequisite, natural or aided. Singapore Airlines currently accepts candidates with refractive errors of not more than 600 degrees myopia and 200 degrees astigmatism. Normal colour vision and field of vision are also required. Regular eye tests are conducted after the age of 40.

Driving.

The minimum criterion for driving is a vision sharpness (acuity) of 6/12 on the Snellen chart, with optical aids such as glasses or contact lenses if necessary, in at least one eye. Colour vision is not an absolute criterion, but drivers need to be able to differentiate the traffic light colours.

In Singapore, it is illegal to drive with eyesight poorer than 6/12 in the better eye. Failure to comply can jeopardise public safety and land offenders in court. Visual field tests are required when eyesight is very poor (6/36) in the worse eye, and needs to satisfy at least 120 degrees arc horizontally.

Significant symptoms such as double vision and poor visual fields from eye diseases or strokes also preclude one from driving. Eyesight is tested at the driving centres upon initial licence application, and is part of a medical examination for renewal of driving licence at 65 years old, repeated once every three years thereafter.

Commercial drivers (taxis, buses and heavy vehicles) require at least 6/12 vision in each eye. For them, additional driving proficiency tests are required at 65 years old, and annual medical checks repeated up till the 70th year, following which enhanced proficiency and medical tests are required.

Apart from the above professions with well-regulated pre-employment standards, several other occupations also count good sight as an asset.

For example, although only colour vision is tested in recruits of the fire brigade, it is desirable that fire-and-rescue specialists have good vision to perform their duties. Similarly, police officers and aircrew members benefit from good sight. Commercial and recreational divers, swimmers and enthusiasts in outdoor sports also rely on good vision for safety in their activities.

From my experience as a Lasik surgeon, many of the above do sign up voluntarily for laser vision correction to improve performance and reduce dependence on cumbersome optical aids.

Work at heights.

The fact that vision is not commonly tested for labourers whose jobs involve working at heights, may reduce workplace safety. I argue that responsible employers test for satisfactory vision and depth of vision for such job requirements prior to placements, to reduce fall hazards and fatalities.

Surgeons.

Several years ago I was asked to perform an eye test for a foreign surgeon who had colour deficiency, and contribute to an assessment for his training. It was a big dilemma. It is wise to steer away from occupations that involve life and death if one has abnormal colour and depth perception, as they can compromise surgical competence.

To conclude, regular monitoring of vision is highly recommended from young. In children, efforts to curtail myopia progression will provide greater career choices. In adults, vision correction via lasers and surgeries are successful in improving visual performance, and in the elderly, maintenance of good vision can keep one actively engaged.

And to clarify: the impressive blind skiers at the start of this article are led by able-sighted guides who ski a short distance ahead while constantly communicating with them via a remote hearing device attached to their ears.

As for me, I count myself lucky with good eyesight that allows me to function well as an ophthalmologist, and see well on the snowy slopes to avoid getting in the way of the amazing blind skiers.