Contact lenses are regulated medical devices that sit directly on the surface of the eye, requiring professional guidance for selection to ensure both vision correction and long-term eye health. Choosing the right lens involves considering eye measurements, material science, and personal habits. The eye care practitioner is the only person qualified to determine the best lens for an individual’s unique physiological needs, ensuring the lens fits properly and delivers sufficient oxygen.
The Essential First Step
Selecting contact lenses begins with a comprehensive eye examination and a specialized contact lens fitting. A prescription for eyeglasses is insufficient because glasses sit approximately 12 millimeters away from the eye, while a contact lens rests directly on the cornea. This difference in distance, known as vertex distance, requires a mathematical adjustment to the prescription power, especially for stronger corrections.
The fitting involves several measurements unique to the eye’s anatomy, including the curvature of the cornea, or base curve, which is measured with a keratometer. The base curve must precisely match the lens curvature to ensure a stable, comfortable fit that allows for proper tear exchange underneath the lens. The practitioner also measures the pupil and iris diameter to determine the overall lens size and assesses the tear film quality.
Assessing the tear film is important, as poor tear quality or quantity can lead to dryness and discomfort with lens wear. Based on these measurements and an overall health check of the eye, the practitioner selects a trial lens. The fit is then evaluated under a biomicroscope to ensure the lens moves correctly and centers well.
Understanding Lens Replacement Schedules and Materials
A significant choice involves the lens replacement schedule, which directly impacts convenience, hygiene, and cost. Daily disposable lenses are the cleanest option, as a fresh, sterile pair is used each day and requires no cleaning solution, offering the lowest risk of infection. Weekly or bi-weekly lenses must be cleaned and disinfected nightly and replaced after one or two weeks of use.
Monthly disposable lenses offer the lowest cost per day but demand the most diligent care routine, including cleaning, rinsing, and storage in fresh solution every night. The material composition of the lens is equally important and falls mainly into two categories: hydrogel and silicone hydrogel. Hydrogel lenses are made from water-containing plastics that rely on their water content to transport oxygen to the cornea.
Silicone hydrogel is a newer material that incorporates silicone, a substance highly permeable to oxygen. This material allows significantly more oxygen to reach the cornea, sometimes up to six times more than traditional hydrogels, particularly for extended wear. While hydrogels can be comfortable due to their high water content, silicone hydrogels are preferred for their superior oxygen transmissibility, which reduces the risk of corneal swelling and hypoxia.
Choosing Lenses for Specific Vision Needs
Beyond standard spherical lenses that correct simple nearsightedness or farsightedness, specialized lens designs address more complex vision issues. Toric lenses are required for correcting astigmatism, a condition where the cornea or lens is shaped irregularly, like a football instead of a baseball. These lenses have different powers in different meridians and rely on stabilization mechanisms, such as thin-thick zones or prism ballasting, to maintain the correct orientation on the eye.
For individuals experiencing presbyopia, which is the age-related inability to focus on close objects, multifocal or bifocal lenses are available. These designs incorporate multiple prescription powers—for near, intermediate, and distance vision—into a single lens. Multifocal lenses allow the wearer to see clearly at various distances without needing reading glasses.
While soft lenses are the most common, rigid gas permeable (RGP) lenses are another option, particularly for severe astigmatism or certain corneal conditions. RGP lenses provide exceptionally sharp vision and are highly durable, but they require a longer adaptation period for comfort.
Important Lifestyle and Comfort Factors
The final choice of lens must align with the individual’s daily life and environment. People working in dry, air-conditioned offices or dusty conditions may experience increased contact lens discomfort. For these individuals, lenses specifically designed for moisture retention or those with low dehydration rates are often recommended to maintain comfort throughout the day.
The care routine is a further consideration, as non-daily lenses require specific cleaning solutions to prevent deposit buildup, such as proteins and lipids from the tear film. Poor hygiene with reusable lenses is a common cause of eye irritation and infection. Therefore, the ability and willingness to consistently follow a hygienic regimen is a determining factor in choosing a lens replacement schedule.
Some people choose cosmetic or colored lenses, which are available with or without vision correction. Even non-prescription colored lenses are medical devices and still require a proper fitting to ensure the lens diameter and base curve are appropriate for the eye.