DiveSight - The only web site specializing solely in prescription dive masks and corrective swim goggles

About eyesight

This page explains a little more about the whole process of ‘seeing’ and what happens when your vision isn't all it should be...

The problems

The most common difficulties experienced with focusing are due to curvature problems of the eye. This will result in either long sightedness or short sightedness.

Long sight

Long sightedness, ( Hypermetropia ) makes it difficult to focus on close objects.

Short sight

Short sightedness ( Myopia ), makes it difficult to focus on distant objects. This can be further complicated by a condition called astigmatism.


This is caused when the eye loses its spherical shape and becomes shaped more like a rugby ball.

Astigmatism makes it more difficult to focus at any distance. It may also occur at an angle, giving even further deterioration in vision.

Correcting the problems

There are three factors to be considered when producing lenses to correct these problems... these are the spherical, cylindrical and axis values, described on our About lenses page.


The sphere value ( Sph ) is the strength of lens needed to correct your focus. A plus sphere ( + ) corrects long-sightedness, a minus sphere ( - ) corrects short sightedness.

Cylinder and Axis

The cyl and axis elements of a prescription compensate for astigmatism.


The Add is short for Reading Addition and is the additional correction required for reading. This is needed to produce bifocal masks ( for reading gauges etc. ) and is mainly required by people over the age of 45.


Your prescription may also contain prism information. If this is the case, we are sorry but we are unable to supply you online, as prism correction requires face-to-face consultation.

Precise correction, Optimum Vision

As eyecare professionals, DiveSight will not work to ‘approximate’ values. We will produce your mask to your precise prescription, exactly as your optician does when making-up your spectacles. We correct spherical, cylindrical and axis values, to ensure that you achieve the optimum visual accuity... or, to put it in plain English, to make sure your underwater vision is as good as it possibly can be. We are able to supply lenses to to high prescription (HP) values, but these may require us to recommend the use of a mask with smaller lenses or larger volume, as the increased thickness of high prescription lenses may position them too close to the eyes or facial features if a low-volume mask is used.

Pupillliary Distance

One further piece of information is needed to ensure optimum vision correction This is the Pupilliary Distance or PD... the distance between the centres of your pupils, measured in millimeters. The simple procedure for making this measurement can be found on our Supplying your Prescription Details page. This enables us to ensure that the optical centres of the lenses line-up with the centres of your pupils, ensuring maximum visual comfort.

Running with Search Engine Friendly Mod 5.7