The first contact lens was developed by a German glassblower, F.E. Muller, in 1887. Glass was primarily used to construct contact lenses until the late 1940’s, and the performance and comfort of contact lens has improved significantly since that time.
Contact lenses and eyeglasses are often used to correct the same vision problems. In general, eyeglasses are less expensive, require less care, and are easier to keep than contact lenses. However, contact lenses provide improved peripheral vision and less distortion than eyeglasses, and patients with active work or leisure lifestyles find contact lenses to be less of a hassle. Some patients also prefer to wear contact lenses instead of glasses for cosmetic reasons. It should be noted that even the most faithful contact lens wearers should always have an updated pair of eyeglasses to wear when contact lenses need to be removed for cleaning, sleeping or to alleviate an eye problem. In addition, patients may also need to use their glasses if they lose a contact lens.
Midwest Eye Care offers its patient nearly 100 different types and brands of contact lenses, but only a few lenses may be useful for each patient. The following variables are considered when an eye doctor or opticians determines which lenses might be suitable for you:
- Degree of myopia (near-sighted) or hyperopia (far-sighted)
- Degree of astigmatism (irregular shape of the cornea)
- Presbyopia (loss of crisp near vision, typically beginning at age 45)
- Existing corneal warping due to past lens wear
- Presence of corneal disease
- Prior eye surgeries
- Hours per day of lens use
- Lens replacement routines
- Cleaning routines
- Work duties, hobbies and sports activities
- Eye dryness and tear production
- Past experience with contact lens wear
The two major categories of contact lenses are ‘rigid’ and ‘soft.’ Rigid contact lenses maintain their shape when placed in the eye, and include the subcategories of hard lenses and gas permeable lenses. Soft lenses are more flexible lenses and include the subcategories of durable, disposable, daily and extended wear lenses.
Hard lenses are perhaps the oldest type of lens still in wide use. These lenses can often be used for several years if a patient’s prescription does not change, and the lens is easy to clean and less expensive over its wearing life. These lenses do have a longer adaptation period and, because they do not form fit to the eye, they may dislodge more easily than a soft lens. Because oxygen does not pass through a hard lens, these lenses are not routinely worn the entire day every day.
Gas permeable (GP) lenses are similar in design to hard lenses, but the materials used for GP lenses allows oxygen to reach the cornea. Corneas need a constant supply of oxygen to stay healthy and comfortable, and in the past five years there have been exceptional advances for this type of lens. GP lenses are more expensive than hard lenses, but they can last several years and provide increased comfort. Like hard lenses, GP lenses require periodic cleaning and are easy to handle.
Soft durable lenses can withstand a wearing cycle of 3 months to 2 years, depending on the patient’s wearing patterns and cleaning habits. Soft durable lenses provide high levels of comfort, can often be worn all day, and are rarely dislodged. However, they are more expensive than hard lenses, need to be disinfected daily, and can be damaged by hairspray, smoke and other common environmental factors.
The disposable lens description now covers many different options, including extended wear lenses, monthly lenses, one- to two-week lenses, and daily lenses.
Extended wear lenses, such as the Focus Night & Day lens, are designed to be worn 24 hours a day for approximately one week. These lenses are ideal for patients who have difficulty handling lenses and are willing to comply with their doctor’s request that the lenses not be worn for more than a week. The extended wear lenses do become dirty after approximately a week, and they are discarded at that time. Some eye doctors are hesitant to prescribe extended wear lenses to adolescents and young adults who are likely to over-wear these lenses.
A clinical trial performed prior to the FDA’s approval of the Focus Night & Day lens revealed that 67% of patients in the trial could tolerate the lenses 22 to 30 days. Consequently, patients must work with their eye doctors to determine the number of days that they can wear these lenses safely and comfortably.
Although these lenses are considered ‘safer’ for extended wear, patients are still at risk for complications caused by wearing the lenses too long. Extended wear lenses have an increased risk of corneal ulcers (a vision-threatening infection affecting the outer, clear cover in the front part of the eye), redness, eye discomfort, foreign body sensation, excessive tearing, and vision changes.
Monthly, one- to two-week, and daily disposable lenses are available from most major contact lens manufacturers. Monthly lenses tend to be more durable than daily lenses, are less expensive over a year’s period, but they do require some cleaning. Daily disposable lenses are perhaps the most convenient type of lens; the lens is discarded at the end of the day and a new lens is inserted the next morning. While more expensive, daily disposable lenses may be ideal for adolescents who have difficulty complying with the cleaning requirements of monthly or durable lenses.