What is a Contact Lens Fitting?
Contact lenses or simply contacts are thin, clear plastic discs (medical devices) placed directly on the surface of the eyes to improve vision in individuals with vision problems. Contacts float on the tear film that covers your cornea (the clear outer layer of the eye). Like glasses, contacts correct vision problems caused by refractive errors and help you see more clearly. A refractive error is when the eye does not refract (bend or focus) light properly into the eye resulting in a blurred image. Contacts can improve vision for individuals with these refractive errors:
- Hyperopia (farsightedness)
- Myopia (nearsightedness)
- Astigmatism (distorted vision)
- Presbyopia (changes to near vision that usually happen with age)
Contact lens fitting is a process in which your physician carries out a detailed eye exam to measure your eyes, check their health, and help determine a comfortable fit, type, and brand of contact lens that fits your eyes and improves your vision.
The advantage of contact lenses over traditional prescription glasses is that they do not obstruct your vision as eyeglasses do. Contacts move with the eye and offer more natural vision. In addition, they are easier to put on when being active or playing sports. They do not fog up the way eyeglasses do, so they may also be more convenient for individuals who spend or work a lot of time outdoors in cold weather or indoors in places that are very cold. Contact lenses come in different shapes, materials, and strengths to suit the patient's needs.
Taking Measurements for Contact Lenses
Each individual’s eyes are mildly different. Some corneas are shallow, while others are steep. Some individuals may have slight astigmatism, while others may have severe, and some may not have it at all. All these considerations make corneal measurements a very crucial starting point. Your eye’s curvature will first be measured using a measuring device known as a keratometer. This is a simple procedure, in which you simply rest your chin on a support while the instrument takes photographs of your eye. These photographs are utilized to analyze reflections of light from your cornea to help the doctor determine the exact curvature of your eye and the size of contact lens that you will need.
In instances in which an individual is found to have a hard-to-fit cornea, based on an unusual curvature of the eye, further computerized measurements are commonly obtained utilizing corneal topography, allowing a more exact image of the shape of the corneal surface. It is also crucial to get an exact measurement of the pupil, the opening at the front of the eye where light enters, as well as the colored part of the eye, the iris. This is measured either with an automated device or a ruler. A tear film evaluation may also be performed to assess if you are susceptible to dry eyes. If you are, specialty lenses may be prescribed to help prevent dry eye symptoms such as itchy, red, and uncomfortable eyes and keep the eye properly hydrated.
Types of Contact Lenses
The two most common types of contact lenses are hard and soft contact lenses.
- Hard Contact Lenses: The most common type of hard contact lens is known as a rigid gas permeable (RGP) lens. These lenses are typically made from plastic along with other materials. They hold their shape firmly, yet they allow oxygen to flow through the lens to your eye. RGP lenses are particularly helpful for individuals with astigmatism and a disorder called keratoconus. This is because they offer sharper vision than soft lenses when the cornea is unevenly curved.
- Soft Contact Lenses: Most individuals prefer to put on soft contact lenses. This is because they tend to be more comfortable and there are many choices. Some of the types of soft lenses include:
- Daily wear contacts
- Extended wear contacts
- Toric contacts
- Colored (tinted) contacts
- Decorative (cosmetic) contacts
- Hybrid contact lenses
- Scleral contact lenses
- Contacts for presbyopia
Fitting of Contact Lenses
After taking all the required measurements, your physician will know what shape and type of contact lenses will fit you better. Many physicians provide their patients with a trial pair of lenses to try on at this point. An instrument called a biomicroscope may be utilized for a magnified view of the cornea with the contacts in, to evaluate the fit. This same instrument can also be utilized to identify and evaluate any change in the eye's health after starting to wear contact lenses. You will also have many follow-up visits after the initial fitting to ensure that your eyes are healthy with the contact lenses on. Your physician should be able to order a permanent prescription for your contact lenses after the second or third visit, assuming that the trial pair contacts fit you well, you are comfortable with it, and there is no harm to your eyes from the trial pair. It is important that your lenses are exactly fitted to your eyes for maximum comfort and health at all times.
