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From the lane to the seabed: the right correction depends on the distance, your technique and what you really want to see.
At the swimming pool, all you need to do is recognise the edge of the pool, read the stopwatch and find your way around the changing rooms. During a dive, on the other hand, you may need to make out a detail on the seabed, check your dive computer and see your dive partner clearly. These requirements may seem similar, but from an optical point of view they are not.
That is why prescription swimming goggles and a prescription diving mask are not chosen simply by copying the numbers from your everyday glasses. The optician’s prescription is the starting point; the optical design must then take into account the lens type, the distance at which the swimming goggles or mask will be used and the level of precision actually required.
It’s simple for you: just bring your prescription and tell us what you want to do in the water.
We’ll take care of choosing the model, checking the fit and converting the data into a suitable solution. You don’t need to calculate or interpret any parameters yourself.
Why everything looks different underwater
The human eye is designed to function in air. When immersed directly, water and the cornea have relatively similar indices of refraction: the cornea loses much of its ability to refract light and vision becomes blurred. A mask or goggles create a small air pocket in front of the eyes, allowing the visual system to focus again.
But that air gap introduces another effect: through the water-glass-air interface, objects can appear larger and closer. Added to this are the shape and curvature of the lens, the distance from the eye and the geometry of the mask. That is why simply talking about ‘one dioptre less’ is too simplistic: the refractive index It explains the principle, but the end result depends on the system as a whole.
In some standard solutions for short-sightedness, a slightly lower negative power is chosen compared to that of spectacles, partly because the image appears magnified underwater. However, this is not a universal rule: astigmatism, differences between the two eyes, high prescriptions and the chosen model can all influence the decision. These are technical assessments which we carry out directly at the Centri Isolani.
First question: what do you want to see?
The scale isn’t chosen in a vacuum. It starts with a very specific question: what is the visual task?
1
Finding your way around
Being able to see the pool edge, the ladder, your own towel, or move around with confidence before and after a swim. A practical, simple and sturdy solution is all it takes.
2
Training
Recognising lanes, reference points, teammates and the stopwatch requires stability. Fit, grip and the difference between the right and left eyes also become important.
3
Explore
When it comes to snorkelling and diving, the seabed, your diving partner, your equipment, photography and close-up reading are all important. Here, a rough estimate may not be enough.
Prescription swimming goggles: simple, but not just any old pair
Many prescription swimming goggles use spherical lenses that are already available in standard strengths. These are affordable options, often costing just a few tens of euros, and for regular short-sightedness they can offer the freedom needed in the pool without having to resort to contact lenses.
Here, too, the focus shifts: in the swimming pool, there’s no need to look out to the open sea. You need to be able to make out the line on the pool floor to swim in a straight line, the pool edge, your own lane and the instructor; before and after your session, it’s useful to be able to find your way around and retrieve the right slippers and bathrobe — not your neighbour’s. For those with moderate to severe short-sightedness, those few metres between the pool edge and the bench are by no means a minor detail. These distances and priorities differ from those of a diving mask designed for exploring the seabed.
It is therefore not just a summer activity: swimming lessons, training sessions and indoor swimming pools are available to children and adults all year round. Being able to recognise landmarks, the instructor, the lane and the surrounding environment with confidence makes the activity feel more natural, even during the winter months.
‘Standard’, however, does not mean ‘the same for everyone’. If your two eyes have different prescriptions, it is best to choose a model that allows for two different lenses. If you have astigmatism, a significant difference between your eyes or a more complex prescription, using only the spherical power may provide useful vision but not necessarily accurate vision.
The fit is also important: goggles that are too stiff, unstable or unsuitable for the shape of your face may let water in, put unnecessary pressure on your face or slip out of place when you move. The correct prescription is only really effective if the goggles stay in the position for which they were chosen.
Graduated diving masks: from the seabed to the computer
In diving, visual clarity isn’t just about the view. The dive computer must be instantly readable: depth, dive time, no-stop limit and ascent rate are essential pieces of information; when the instruments are integrated, they can also display pressure and gas remaining. Added to this are the ability to recognise your dive partner and clear environmental landmarks. For this reason, your choice may extend beyond the pre-fitted lenses available for some models.
Standard interchangeable lenses are practical when the correction is predominantly spherical and falls within the specified power range. Customised lenses, on the other hand, allow for astigmatism, significant differences between the two eyes and higher prescriptions to be taken into account. Lenses can be made as either bifocal or multifocal. The bifocal solution creates a defined zone for the dive computer and instruments, leaving the area for viewing the seabed wide and unobstructed; a multifocal or progressive design can also provide a more gradual transition for intermediate distances. The choice depends on the activity, the position of the instruments, the reading posture and the mask used. The size, height and position of the optical zones cannot simply be copied from ordinary reading glasses.
Not every frame is suitable for every prescription. The internal volume, the shape of the lenses, the distance from the eyes, the field of vision and the fitting options are all part of the same design. The fitting test is therefore carried out before the lenses are fitted.
The same requirement can lead to two different solutions
Someone might want a pair of affordable, durable goggles for training twice a week, so they can see the lane and their stopwatch clearly. The same person, whilst diving, might need to read a display up close, observe small details and maintain a sharper view at a distance.
The starting point is the same, but the required precision, distances, field of view and geometry of the solution differ. This does not mean ‘inventing’ two prescriptions: it means correctly adapting the optometrist’s prescription into two coherent optical designs for different activities.
The real test takes place in the context for which the solution was designed.
Putting on prescription goggles or a mask and judging them by looking out of the water is the most common mistake: they may seem too strong or simply ‘strange’, but that is not the environment in which they are intended to be used. The aim of the project is to see underwater; it is there that the quality of the display must be assessed, taking into account the purpose for which the solution was designed.
To understand the starting figures, please refer to the entry dioptre from the Isolani Glossary. To find the solution, however, all you need to do is provide us with the prescription and intended use: there’s no need to interpret a table.
What about contact lenses in water?
Contact lenses and water are not a combination to be taken lightly. The latest guidance from the CDC recommends removing them before swimming, showering or getting into the bath: water can damage the lenses and increase exposure to microorganisms that can cause infections, some of which can be serious.
For those who want to see clearly in the pool, prescription swimming goggles are often the simplest option. For diving and specific situations, the choice should be assessed on a case-by-case basis, without presenting contact lenses as a one-size-fits-all solution. If accidental contact with water occurs, the lens should be removed as soon as possible and handled in accordance with the recommended procedure.
Find out more about use, maintenance and rotation in the A comprehensive guide to contact lenses and as part of the process of Isolani Advanced Contact Lens Practice.
When the sea came into the shop
Underwater vision is part of the History of the Isolani Optical Institute long before it became a technical specialism. The Cressi’s official history It is said that the brothers Egidio and Nanni began handcrafting masks in Genoa in 1938, unveiled the ‘Sirena’ in 1943 and officially founded the company in 1946.
It is against this same pioneering backdrop that a memory cherished by the Isolani family – gathered over the years through the stories of Alberto Isolani, Dino’s grandson. Dino Isolani worked with Cressi to develop the first optical solutions for diving masks. It was a process involving trials, lenses, faces and the sea: the correction had to work in a real-world environment, not just on the optician’s counter.
As there is currently no technical documentation available to allow for a verifiable attribution of the patent, we preserve this account in the form in which it has come down to us: a family account, consistent with the Genoese origins of the first Cressi masks. It is also the thread that links that era of craftsmanship to today’s approach: always starting from what the diver actually needs to see underwater.
How we develop the solution at the Centri Isolani
These solutions cannot be configured online because a prescription alone does not provide all the necessary information. The fit on the face, the seal, the distance between the lens and the eye, the model and what you want to see are all factors beyond the simple lens prescription. Without knowing these, a solution might not work properly precisely where it’s needed most: underwater. In person, however, the process is quick and straightforward, and we’ll take care of these checks for you.
1. Let’s start with the prescriptionWe measure the sphere, cylinder, axis, and any differences between the two eyes.
2. Let’s define the useSwimming, the sea, snorkelling, diving, equipment or photography all have different priorities.
3. Let’s try out the modelFit, stability, volume, distance from the eyes and field of vision are checked on the face.
4. Let’s choose the projectA standard solution when that is sufficient; bespoke manufacturing when greater precision is required.
Discover the others Isolani solutions for sport, swimming and outdoor activities or find the Nearest Isolani Opticians.
Frequently Asked Questions
Can swimming goggles be fitted with prescription lenses?
Yes. There are models with spherical lenses in standard powers, as well as options that allow you to choose different powers for the right and left eyes. Compatibility depends on your prescription and the model.
Do I need to use the same prescription as my glasses?
The prescription is the starting point, but it should not be copied automatically. Enlarged underwater images, available ranges, astigmatism, differences between the eyes and the geometry of the solution may require a specific technical approach.
Can a diving mask also correct astigmatism?
Standard interchangeable lenses primarily correct the spherical component. With a bespoke fit, it is also possible to take into account the cylinder and axis, subject to the frame chosen.
Are there bifocal or multifocal lenses available for reading a dive computer?
Yes, we offer both options. The bifocal lens provides a specific zone for computers and instruments; the multifocal lens can also handle intermediate distances more gradually. The choice depends on the intended use, the position of the instruments, the reading posture and the type of mask.
Can I check the lens strength by trying the goggles on out of the water?
This is not a reliable test: a solution designed for underwater vision may appear different when used on the surface. The result should be assessed underwater and in relation to the visual task for which it was designed.
Can I swim with contact lenses under my swimming goggles?
Prevention guidelines recommend removing contact lenses before swimming. Prescription swimming goggles mean you don’t have to rely on contact lenses as a standard solution when in the water.
Is a standard lens or a custom-made mask better?
It depends on the visual task. A standard lens may be sufficient for standard spherical correction; complex prescriptions, instruments, photography or precision requirements may call for a bespoke design.
Sources consulted: CDC, Divers Alert Network, PADI, the official Cressi chronology and manufacturers’ documentation. The account concerning Dino Isolani is presented as a family memoir compiled from the recollections of Alberto Isolani; technical sources verify the general principles. The optical solution is determined on a case-by-case basis according to prescription and intended use.
The information on this page is provided for information purposes only and relates to the optical and commercial sectors. It does not contain any medical, clinical or diagnostic content.