The ABC of contact lens options

With so many different types of contact lenses in the market, and with new products released on a regular basis, it can be hard to keep up with the options available. Here, we take a back-to-basics approach and explore the main types available.

Material facts

There are two main types of contact lenses that patients can be fitted with: soft and rigid gas permeable (RGP). Soft lenses are the ones you will probably be most familiar with.

These are made from a material called hydrogel, which is a mixture of plastic and water to make the lenses soft and comfortable to wear.

A newer material for soft contact lenses is called silicone hydrogel, which incorporates silicone in them to make them even more comfortable and breathable, so they are suitable to wear for long periods of time.

RGP or ‘hard’ lenses are made of a much firmer material than soft lenses and, as the name suggests, are much harder and not as flexible. They are typically replaced every year. RGPs are much less common than soft lenses these days, but are fantastic for patients with complex prescriptions as they can be custom made to sphere powers of around ±40D. They can also correct cylinder powers up to about 12D for patients with high levels of astigmatism.

Ortho-k is a great alternative to laser treatment for those that don’t want a surgical option

The long and short of it

Depending on the patient’s prescription they may require spherical, toric or multifocal lenses. Spherical lenses correct for shortsightedness (myopia or ‘minus’ prescriptions) and longsightedness (hyperopia or ‘plus’ prescriptions)in patients who have no or small amounts of astigmatism. Toric lenses are designed to correct for shortsighted and longsighted prescriptions as well as astigmatism. This usually applies to patients who have 0.75D cylinders or more.

Multifocal lenses are for ‘those of certain age’ and require an add. They allow both distance and reading prescriptions to be corrected. In the most common types, a concentric circle design is used so that as light passes through the pupil, part of the light is focused for distance and the other part for reading. As the light is split in this way, it can compromise the vision slightly compared to spectacles, so it may take a little while for the patient to get used to them.

The vanishing trick

RGP lenses can also be used for a technique called orthokeratology (ortho-k). Ortho-k is one of the big innovations in contact lenses and has become increasingly popular over the past decade. It allows, mainly, shortsighted prescriptions to be corrected non-surgically, removing the need for any contact lenses or spectacles during the day.

Ortho-k involves patients wearing a specially designed RGP lens overnight. While the patient is asleep the lens gently reshapes the front surface of the eye (cornea) so that they can see clearly the following day after removing the lenses. In other words, a patient could be -4.00D prior to ortho-k but after wearing lenses regularly overnight they will be plano throughout the day. Pretty magical when you think about it.

Ortho-k is a great alternative to laser treatment for those who don’t want a surgical option and can also slow down the progression of shortsightedness in some children.

Image credit: CooperVision