What is the best solution for divers who need glasses topside? Contact lenses, stick-on lenses, bonded prescription lenses or manufacturer-supplied prescription masks? Mark ‘Crowley’ Russell looks at the options
With the exception of the brain, eyes are the most complex organs ever to have evolved in the animal kingdom. Unfortunately – at least in the case of humans – that evolutionary process hasn’t quite finished yet. Each component of the eye is prone to a variety of aberrations, any one of which can have a significantly detrimental effect on a person’s eyesight.
For scuba divers, the effects of visual impairment can range from mildly frustrating to lethal. Seeing the blurred outline of a passing whale shark, or not spotting a rare nudibranch, is annoying but not dangerous. The inability to focus properly on a dive computer or gauge, however, could easily result in a trip to the chamber or cause an out-of-of air situation. For technical divers and cave divers, where limits and gas percentages have a much more critical role to play, misinterpreting a computer’s display could have an outcome that is significantly worse.
There are a number of factors behind the causes of visual impairments, including genetic malformation, disease, and – as with so many other things – the passage of time. Eye disorders brought on by conditions such as glaucoma, cataracts and diabetes require medical treatment or surgery, but by and large, defects in the optical elements of the human eye can be aided by the application of corrective lenses. These are collectively known as Refractive Visual Impairments and can be broadly split into four main categories: myopia, hyperopia, presbyopia and astigmatism (see the Visual Impairments box below).
Scuba divers often find that the magnifying effect of wearing a mask underwater will compensate for minor visual imperfections. Divers who have more complex corrective requirements, however, will find this insufficient. At the surface, treatment for most refractive visual impairments is relatively straightforward. Any high street optometrist can perform an eye test and issue a prescription for spectacles or contact lenses specifically tailored to the eyes of the wearer. Cheap, off-the-shelf readers can be purchased by those with presbyopia (see the Understanding Prescriptions box below).
Underwater, the application of corrective lenses is not quite as straightforward, but there are several different options available to scuba divers with visual impairments. Each comes with its own set of pros and cons and will depend to a large extent on what type of diving the wearer is undertaking, how often they dive, and the level of correction required.
SeeDive Push-on lenses
An inexpensive solution for those with reading difficulties. Retailing between around £20-£40 for a set, they can be cut and trimmed to fit the lower half of most masks, effectively making the mask bifocal. Although most divers who use push-on lenses swear by their success, some report that the inserts have come loose during a mask flood or have become lost in the rinse tank. SeeDive lenses are a popular product, a scuba diving equivalent to off-the-shelf ‘readers’, and are available in powers of +1.0 to +4.0, in 0.5 dioptre increments, +5.0 and +6.0, at £42 a pack.
PROS: Inexpensive, and effective for divers who otherwise squint at their gauges or dive computers.
CONS: Possibility of mid-dive movement or loss.
Many divers opt to dive with contact lenses and a regular mask. For the purposes of corrective vision, this is a very flexible and initially very inexpensive solution, although the cost – including aftercare – may mount rapidly for regular divers. For simple distance prescriptions, boxes of 30 disposable, distance-corrective lenses are available in 0.25 dioptre increments for less than £10 (you will, of course, need two boxes if the right and left eye have different prescriptions); bifocal (distance and reading) and toric lenses (distance and astigmatism) are available from around £20.
Contact lenses are prone to be dislodged during mask flooding and clearing, which would be most inconvenient if you did not have a spare set in your kit bag. There are, however, problems associated with contact lenses in the marine environment that can be much more serious if proper care is not taken. Various bacteria can become lodged under the lens and lead to infection; the saltwater can cause the lens to become stuck to the eye, and hard contact lenses may cause the diver to experience blurred vision after a dive, as nitrogen is unable to escape the cornea properly.
None of these problems is insurmountable but the best advice is to rinse or replace the contact lens after each dive and carry an adequate supply of spares and contact lens solution on dive trips.
PROS: Cater to a wide range of prescriptions. Inexpensive for irregular divers.
CONS: Possibility of mid-dive loss, potential infection or damage to the eye through improper care. Cost can mount over time for regular divers.
Bonded full-prescription lenses
By far the best long-term solution is custom-made lenses, ground by an ophthalmic specialist to match your precise prescription, which are subsequently bonded to the dive mask. They come at a high price, however, the lenses can be constructed to cater for a combination of distance, astigmatism and reading impairments. Due to the specialist equipment and expertise needed to create a custom prescription, costs begin at around £180 for a set of lenses, not including the price of the mask. Most companies can either fit to your existing mask or supply a fairly wide range of masks from top manufacturers for you to choose from.
The full range of bifocal, split-lens and lenses for severe astigmatisms can be supplied to the exact needs of your prescription. They are a preferred choice for technical divers – particularly cave divers – who cannot risk losing an insert or contact lens mid-dive. Bonded prescription lenses are also important for underwater photographers and videographers, who rely on the most accurate vision to take the most perfect shots. There is a limited number of ophthalmic mask specialists around the world.
PROS: As close to perfect underwater visual acuity as possible. Long-term solution.
CONS: Expensive to purchase and replace.
Prescription lenses for dive masks
Most manufacturers offer at least one model of mask that can be ordered with prescription lenses, some of which need to be factory-fitted, others are user-changeable (although fitting by a dealer is recommended), and some newer masks have quick-release mechanisms allowing for the lenses to be changed at the wearer’s convenience. Lenses are available in 0.5 dioptre increments, some as a symmetrical pair, others as individual right-and-left lenses. A limited number of masks are available with the option of bifocal lenses for reading.
Prescription lens dive masks are a convenient, relatively inexpensive and long-lasting solution for visual impairment underwater, but may not satisfactorily fulfil a diver’s prescription. The following is a sample of masks that are currently available with optical lenses.
PROS: Inexpensive long-term solution.
CONS: Only compensate for distance problems, not astigmatism. The 0.5 dioptre increments leave a margin for inaccuracy.
TUSA Freedom Ceos
Mask £65.50, lenses £32.50 each
Among the manufacturers that produce masks with corrective lenses for divers, TUSA ranks highly for its available options. The lenses are available in a wide range of dioptres for correcting distance vision, plus bifocals are available for reading correction. The lenses fit not only the popular Freedom Ceos, but also the Geminus (£58) and Splendive II (£42) models. TUSA’s new Paragon mask (£169.95) also has corrective lenses available, priced at £54 each but only in negative dioptres from -1.0 to -6.0.
Distance: -1.0 to -8.0; +1.0 to +4.5, 0.5 dioptre increments
Bifocal: +1.0 to +4.5, 0.5 dioptre increments
TUSA Universal Optical Frame £19.99
TUSA also make a Universal Optical Frame for all TUSA sport mask models. The frame is priced at £19.99 and is fitted with identical
dioptre lenses of -2.0, -3.0, -4.0, -5.0 or -6.0.
Scubapro Zoom EVO
Mask £44, lenses £28.50 (distance), £48 (bifocal)
The Zoom EVO is a low-volume mask featuring a quick-release lens-changing system that allows divers to swap lenses, without tools, in under a minute. A range of colour options to match Scubapro’s Hydros Pro BCD and Seawing Nova fins are available for the colour-coordinated diver. Lenses are available for distance and reading correction.
Distance: -1.5 to -8.0; +1.5 to +4.0, 0.5 dioptre increments
Bifocal: +1, +2, +3
Atomic Aquatics Subframe
Mask £99.95, lenses £54.95 (distance), £79.95 (bifocal)
Atomic Aquatics’ most popular mask, the Subframe, comes in a wide range of colours and is available in regular, medium and slim fittings. Corrective lenses for distance vision are available
in negative dioptres, and bifocal reading lens options are also available.
Distance: -1.0 to -8.0, 0.5 dioptre increments
Bifocal: +1.5 to +2.5, 0.5 dioptre increments
Mares Chroma Liquidskin
Mask £79, lenses £26 each
Mares’ Chroma Liquidskin also features a quick-release system for swapping lenses without tools. Other available models with the option of corrective lenses are the X-Vision Liquid Skin (£67) and Standard (£45), the X-Vu Liquid Skin (£57) and Standard (£40), and the Opera (£31).
Distance: -1.0 to -7.0; +1.0 to +4.5, 0.5 dioptre increments
Mask £48, £52, £57, lens £30 each
SEAC has five different models of mask that can be fitted with corrective lenses, including the Fox (£32), One (£31), One Pro (£34) and Extreme (£24), along with the featured Italia, which has three separate prices depending on whether you choose a clear skirt, or black skirt with metallic or mirrored finish. Of these, the Italia has the widest range of corrective lenses.
Distance: -1.5 to -6.0; +1.0 to +3.0, 0.5 dioptre increments
Fitting: User-changeable, dealer fitting recommended
BARE Sport Duo B or Duo C
Mask £39.95, lenses £32
Better known for its expansive range of exposure suits, BARE’s optical mask is a low-volume design available with black or clear skirts. A limited range of negative dioptre corrective lenses is available.
Distance: -1.5 to -6.0; 0.5 dioptre increments
Fitting: User-changeable, dealer fitting recommended
Mask £79.95, lenses £30 each
A preferred choice of brand for many technical divers, the M3 is designed to provide the maximum field of distortion-free vision that is available in a low-volume, twin-lens mask. Corrective lenses are available in negative dioptres.
Distance: -1.5 to -8.0, 0.5 dioptre increments
Fitting: User-changeable, dealer fitting recommended
Cressi Big Eye Evo and Evo Crystal
Mask £57/£66, lenses £43-£55 each
Optical lenses for the Big Eyes Evo and Evo Crystal are available in left and right versions in negative dioptres. Cressi’s Focus mask (£40) also has optical lenses available, but the kits have symmetrical left and right lenses in the same dioptre. Prices for Focus lenses range from £36-£55 per lens.
Distance: -1.5 to -6.0, 0.5 dioptre increments
Fitting: Dealer fitting recommended
Refractive visual impairments
The eye functions by refracting light through the cornea, which covers the iris, the coloured part of the eye which dilates and contracts to control the amount of light passing through the pupil. This is then focused by the lens onto the retina at the back of the eye, which passes information to the brain via the optical nerve.
Myopia: also referred to as short- or near-sightedness. It occurs when light entering the eye is focused at a point in front of the retina. Nearby objects appear normal, but distant objects
appear blurry. Myopia is by far the most common form of visual impairment.
Hyperopia: also known as long- or far- sightedness, hyperopia is the opposite of myopia. Light entering the eye is focused at a point beyond the retina causing nearby objects to appear blurry, but distant objects to appear normal. Hyperopia is the least common form of visual impairment.
Astigmatism: this is the most complex of visual impairments, an irregular curvature of the cornea or lens can cause light to be focused not only before or beyond the retina but also unevenly across the retina’s surface. Astigmatism affects around 30 per cent of the population and causes blurred vision at all distances.
Presbyopia: Presbyopia is a natural part of the ageing process, whereby a hardening of the lens prevents the eye from focusing on nearby objects and causes difficulty with the reading of text, especially in poor light conditions. Presbyopia occurs in everybody as they age, however its effect may be more pronounced in some individuals than others. Presbyopia can occur in people with pre-existing conditions, often resulting in the need for bifocal lenses.
Treatment for myopia, hyperopia and astigmatism involves testing by an optometrist (an eye healthcare specialist), or possible referral to an ophthalmologist (a medical doctor for eye conditions), to acquire a prescription for spectacles or contact lenses which can be constructed by an optician.
Presbyopia, for many people, can be treated by purchasing off-the-shelf reading glasses. Laser surgery is available but comes at a fairly eye-watering expense. Prescription lenses are custom-made to suit individual needs. Left and right eyes may often have very different levels of impairment. The following terminologies are generally given for each eye:
Sphere: Spherical lenses are required to correct near- and far-sightedness by compensating for the incorrect focal length of the natural eye. Corrections are given in dioptres (diopters in the US), a measure of the optical power of the lens based on its size and curvature. Negative dioptres are used to correct myopia, and positive dioptres to correct hyperopia and presbyopia.
Dioptres are usually prescribed in increments of plus or minus 0.25.
Cylinder/Axis: Astigmatism is a condition that requires a lens that focuses light into a line, rather than a point, as is the case with spherical lenses. The cylinder strength is given as a dioptre, and the axis is the degree to which the cylinder is rotated to correct the direction of the aberration. Lenses that combine both spherical and cylindrical designs are known as toric lenses
Add: This is an additional prescription, usually to compensate for presbyopia in conjunction with one of the other conditions, resulting in a different optical power in the lower half of the lens, creating ‘bifocal’ lenses.