Contact Lenses 101
Contact lenses were originally developed in 1949 and since then have become an incredibly popular method to correct vision. While the first contact lenses were fragile and expensive enough to create the need for “contact lens insurance,” modern lenses are significantly less expensive and much more durable.
The first modern contact lenses were made of a material called polymethyl methacrylate, also known as PMMA or Plexiglas. Since this material does not allow for oxygen to pass through it did cause a number of adverse clinical effects. Starting in the 1970s and continuing through the 80s and 90s new materials were developed that would allow for oxygen to permeate and reach the cornea. While “soft” contact lenses had been invented (the first breakthrough was published in 1959) it wasn’t until 1998 that the first silicone hydrogel lenses were launched.
Contact lenses work by correcting refractive error in an individual’s vision. Since contact lenses bend light in every direction, this allows for lenses to correct differently on the horizontal axis than the vertical axis. This allows for contacts, known as toric lenses, to correct for astigmatism, which is when the eye is not perfectly spherical. Since the lenses need to be oriented properly on the eye they are weighted and often have marks to assist the doctor in fitting. Other corrective lens options include multifocal lenses (like bifocals) and “monovision.” Monovision involves having two contact lenses with different focal points and the wearer learns to use one eye for seeing close objects and the other to see far.
Some contact lenses can help people with certain types of color blindness differentiate colors better while others are even used to treat and manage eye disorders (like dry eyes or corneal abrasions.) Finally, contact lenses can be used for cosmetic purposes or even a combination of cosmetic and corrective purposes. Some cosmetic lenses change the color of the iris and others are used to make the iris look larger (like a doll’s eyes.) Some cosmetic lenses are used to correct the appearance of a damage or malformed iris.
Contact lenses typically come in three types of “wear schedules.” Daily wear lenses are intended to be worn all day and removed at night before sleeping. Extended wear lenses can be worn all day and night, typically up to 6 consecutive nights. Finally, continuous wear lenses can be used up to 30 consecutive nights. Overwearing contact lenses can cause complications such as corneal ulcers, infections, and corneal neovascularization (excessive ingrowth of blood vessels into the cornea.)
In addition to wear schedules, contact lenses are also categorized by replacement schedules. Single use lenses, or 1-day/ daily disposables, are discarded after one use. These lenses are typically more comfortable because they are thinner and lighter, but this makes them unable to withstand repeated use. Since a new, sterile lens is used each time there is no need to clean or disinfect. Other lenses need replaced after 2 weeks, 4 weeks, or even quarterly and annual. Many of the longer use lenses had been popular, but have been discontinued in favor of the single use lenses. Rigid lenses, which are still occasionally used, could last for multiple years.
Corrective contact lenses require a prescription from an optometrist. While the prescription may be similar to one for eye glasses they are not interchangeable. A standard eye exam will identify and contraindications of use, such as infections, allergies, or dry eyes, and will identify the proper power required to correct vision. Contact lenses are then fitted to the individual and after a trial the doctor can prescribe the ideal lens.