Your eye doctor may recommend custom contact lenses if you can't wear regular contact lenses because of problems such as an irregularly shaped eye or too much astigmatism.
They may also suggest custom contact lenses if regular contacts are uncomfortable or cause vision problems.
Custom-made contacts are available both in rigid gas permeable (RGP or GP) and soft lens materials, and may be able to provide sharper vision and greater wearing comfort than regular GP or soft lenses.
Gas permeable custom contacts
Gas permeable contact lenses generally provide sharper vision than soft contacts. This can be especially true for people with certain types of astigmatism.
But some people find gas permeable lenses difficult to get accustomed to. GP lenses are designed to create 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.
However, the interaction between the edge of gas permeable lenses and the eyelid and the movement of GP lenses during blinks can make these lenses uncomfortable for some wearers.
Also, for individuals with unusually shaped corneas, it may be impossible to fit the eye properly with conventional GP lenses so the lenses remain properly centered on the eye. 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, some contact lens manufacturers offer customized gas permeable lens options.
The fitting and lens manufacturing process for gas permeable custom contact lenses differs from conventional GP lenses in two ways: how your eye is measured and how the lenses are designed.
Eye measurements, lens designs for conventional GP lenses
Understanding how conventional GP lenses are fitted as part of a contact lens eye exam will help you understand the complexities of custom contact lenses.
Most eye care practitioners measure the curvature of the front surface of the 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. The peripheral curves also provide an optimal amount of edge lift so tears can circulate behind the surface of the lens during and after blinks.
Eye measurements, lens designs for GP custom 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 GP custom 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 more closely to the surface of the cornea.
This customized design and fitting process may help create 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 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 GP custom contact lenses?
Someone who is dissatisfied with their vision with conventional soft contacts or who has tried conventional GP lenses and found them uncomfortable may be a candidate for GP custom contact lenses.
And because custom GP lenses can be fabricated to fit unusual corneal surfaces, they often are an optimal solution for individuals with keratoconus or unusual corneal curvature — an eye injury or from an unsuccessful LASIK procedure or other corneal refractive surgery.
Also, multifocal custom gas permeable contact lenses may be recommended for some people with presbyopia.
Soft custom contact lenses
Though most custom contact lenses currently are made of rigid gas permeable lens materials, custom lenses also are available in soft lens materials, including highly oxygen-permeable silicone hydrogel polymers.
A number of contact lens manufacturers offer special design soft contacts for hard-to-fit eyes. These designs feature smaller and larger diameters and a wider range of curvatures and powers than conventional soft lenses for a more customized fit. Some of these manufacturers also offer custom toric contact lenses that correct higher amounts of astigmatism than conventional soft toric lenses.
Most conventional toric soft lenses can correct up to 2.75 diopters (D) of astigmatism and are available in astigmatism-correcting power increments of 0.50 or 0.75 D. Custom toric soft lenses can correct much higher amounts of astigmatism and can be ordered in finer increments (0.25 D) for a more accurate correction and potentially sharper vision.
Other types of custom soft contact lenses include:
- Multifocal toric contact lenses that can correct many combinations of refractive errors and presbyopia.
- Multifocal lenses specially designed for myopia control in children.
- Custom lenses made of advanced silicone hydrogel materials that are fabricated with a lathe-cut process similar to those used to create GP lenses for a greater degree of customization.
Several contact lens manufacturers offer custom soft lenses for a wide variety of applications. During your contact lens exam, your eye doctor will determine whether you require custom lenses and explain which designs are suited to your needs.
As with custom RGP lenses, fitting soft and silicone hydrogel custom contact lenses is more complex than a conventional contact lens fitting and often involves the use of special equipment to measure corneal topography and higher-order aberrations to assist in the design and fitting of the lenses.
Custom contact lens care
Caring for custom contact lenses is no different than caring for conventional GP and soft lenses, and the same contact lens solutions can be used on custom lenses.
Custom contacts often are designed to be worn for longer periods between lens replacements than conventional contact lenses. This makes proper daily lens care even more important to keep the lenses clean and comfortable.
Be sure to consult with your eye doctor regarding the proper wearing time, replacement schedule and care products to keep your custom contacts comfortable and reduce the risk of contact lens-related complications.
Cost of custom contact lenses
Though custom contacts cost more than traditional soft or GP lenses, some people decide that sharper vision than standard prescription contacts or eyeglasses is worth the extra cost. Custom contact lenses may also be recommended as an alternative to LASIK and other types of vision correction surgery.
Because of the added expertise, time and advanced equipment required to fit custom contact lenses, these made-to-order lenses typically cost more than regular contact lenses. If your eye doctor recommends custom contacts, they can advise you of the cost of that particular type of custom lenses.
To see if you're a good candidate for custom contact lenses, contact an eye doctor for a comprehensive eye exam and contact lens consultation.
