Custom Contact Lenses

By Gary Heiting, OD

Custom contact lenses may be for you if you can't wear regular contact lenses because of problems such as an irregularly shaped eye or too much astigmatism.

You also might consider wearing custom contact lenses, adapted specifically for your needs, if regular lenses are too uncomfortable or don't provide sharp enough vision.

Newer technology means custom contact lenses come in both rigid gas permeable (RGP or GP) and soft lens materials that may be able to provide sharper vision and greater wearing comfort than previous contact lens options.

Custom Gas Permeable (GP) Contacts

Most eye care professionals agree that rigid gas permeable contact lenses generally provide sharper vision than soft contacts. This is especially true for people with certain types of astigmatism.

But some people find GP lenses hard to wear. Traditionally, GP lenses have been designed with a slight gap between the edge of the lens and the eye's surface. This "edge lift" enables tears to flow behind the lens during and after blinks to provide more oxygen for eye health.

Unfortunately, the interaction between the edge of GP lenses and the eyelid and the movement of GP lenses during blinks can make these lenses uncomfortable for some wearers.

Also, for individuals with unusual eye surface shapes, it may be impossible for conventional GP lenses to center correctly. This increases the risk of discomfort and variable vision.

To overcome these limitations and enable more people to enjoy clear, comfortable vision with GP lenses, contact lens manufacturers are now using advanced technology to create customized gas permeable lens options.

The fitting and lens manufacturing process for custom gas permeable contact lenses differs from conventional GP lenses in two ways: how your eye is measured and how the lenses are designed.

Eye Measurements and Lens Designs for Conventional
GP Contact Lenses

Understanding how conventional GP lenses are fitted as part of a contact lens eye exam will help you understand the complexities of customized contact lenses.

Most eye care practitioners measure the curvature of the eye's surface (cornea) with an instrument called a keratometer.

The keratometer uses light reflections from the cornea to determine the steepest and flattest meridians of the eye. To picture how this works, imagine that the front of the eye is like the face of a clock. A line connecting the 3 and the 9 is one meridian; a line connecting the 12 and 6 is another meridian, and so on.

The curvature of a conventional GP contact lens is based on three keratometry measurements: the curve of the steepest meridian of the cornea, the curve of the flattest meridian and the orientation of the flattest meridian — in other words, whether the flattest meridian is horizontal, vertical or somewhere in between.

Based on these measurements, the eye care practitioner or lens manufacturer chooses the curves to apply to the back surface of the GP lens for the best possible fit. With a conventional GP lens, the back surface typically has one curve for the central part of the lens (called the base curve) and two or more flatter curves in the periphery of the lens.

These flatter curves help the lens align better to the surface of the cornea, which typically becomes flatter in the periphery. These curves also provide the proper amount of edge lift so tears can pump behind the surface of the lens during and after blinks.

Eye Measurements and Lens Designs for Custom
GP Contact Lenses

Compared with conventional methods, the eye measurements and lens designs for custom gas permeable lenses are much more complex.

Instead of obtaining just three measurements of the cornea from a keratometer, the eye care practitioner who fits custom GP contact lenses uses an instrument called a corneal topographer to obtain curvature data from several thousand reference points on the eye.

These data points form a detailed map of the curvature of the eye, which the eye care practitioner and lens manufacturer then use to design a multi-curved lens surface that conforms much more closely to the surface of the cornea.

This customized design and fitting process creates a more comfortable fit — especially on irregularly shaped corneas and corneas with high degrees of astigmatism.

In addition to being produced with advanced lens fabrication equipment capable of creating surfaces with smoother point-to-point curvature changes, custom GP lenses typically are also made with newer gas permeable lens materials that allow more oxygen to pass through the lens to the eye.

Because these newer materials allow more oxygen to reach the eye directly through the lens, eye care practitioners and contact lens manufacturers do not have to rely on tears pumping underneath the lens to maintain eye health. Therefore, the edge lift of customized lenses can be safely reduced and the curvature of the edge of the lenses can conform better to the peripheral cornea for a more comfortable fit.

Who Can Benefit From Custom GP Contact Lenses?

Nearly anyone who is dissatisfied with their vision with conventional soft contacts or who has tried conventional GP lenses and found them uncomfortable may be a good candidate for custom gas permeable contact lenses.

And because custom GP lenses can be fabricated to fit unusual corneal surfaces, they often are also an excellent solution for individuals with keratoconus or unusual corneal curvature — from natural causes, an eye injury or from an unsuccessful LASIK procedure or other corneal refractive surgery.

Also, multifocal custom gas permeable contact lenses are showing great promise for the correction of presbyopia. And some eye care practitioners report that custom GP lenses are more effective than conventional GP lenses for the non-surgical treatment of myopia and astigmatism when fitting the lenses for orthokeratology.

Custom Soft Contact Lenses

If you have astigmatism and prefer soft contact lenses, custom designs also are available in these lens materials.

Though custom soft contact lenses lack some benefits of custom GP lenses, they can correct higher levels of astigmatism and provide a more accurate correction of astigmatism than conventional toric contact lenses.

Most conventional toric soft lenses correct only up to 2.50 diopters of astigmatism and are available in astigmatism power increments of 0.50 diopters or 0.75 diopters. Custom toric soft lenses can correct higher amounts of astigmatism and can be ordered in finer increments (0.25 diopters) for a more accurate correction and potentially sharper vision.

Professional Advice for Custom Contact Lens Fittings

Even if you don't have a specific problem, custom contact lenses may be right for you if you have been unsuccessful with other lens options. You may be tired of your eyeglasses, and don't like the risks and the expense associated with LASIK or other types of refractive surgery.

Because of the time and extra steps needed for a fitting, custom contact lenses can cost about twice as much as regular contact lenses. Your eyecare professional can advise you of the cost of the particular type of custom lenses best suited for your needs.

To see if you're a good candidate for custom contact lenses, contact an eye doctor near you for a comprehensive eye exam and contact lens consultation.

[Page updated June 2008]