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 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
Most eye care professionals agree that gas permeable contact lenses generally provide sharper vision than soft contacts. This especially is 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.
Unfortunately, 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, contact lens manufacturers are now using advanced technology to create 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 easurements: 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 the proper amount of edge lift so tears can circulate behind the surface of the lens during and after blinks.
