The Eye Examination
A comprehensive eye examination is a series of tests that measure a patient's ocular health and visual status to detect abnormalities in the components of the visual system and to determine how well the person can see. The examination is performed by an ophthalmologist (M.D. or D.O.) or an optometrist (O.D.) to determine any pre-existing or potential vision problems. Eye exams may also reveal the presence of many non-eye diseases such as high blood pressure or diabetes.
The tests conducted during a comprehensive eye examination are generally noninvasive and cause no pain or discomfort. The doctor will perform some of the tests, while a trained technician may conduct others. The doctor, however, will examine the results of all tests and determine what, if any, treatment is required.
Tests performed during a comprehensive exam can be generally divided into two parts:
1. Visual acuity to assess how well a patient sees
2. Eye health to make sure the eye is healthy and functioning properly
Types of Eye Care Professionals
Optometrists, also called doctors of optometry (O.D.), specialize in diagnosing and treating vision problems, eye diseases and related conditions; and prescribe eyeglasses, contact lenses, and medications to treat eye disorders. They cannot perform surgery, but they often provide patients with pre- and post- surgical care. Sometimes ophthalmologists and optometrists work in the same practice and co-manage patients. It was an optometrist who introduced the first plastic contact lens.
An Ophthalmologist, is a physician who specializes in the medical and surgical care of the eyes and visual system and in the prevention of eye diseases and injury. Ophthalmologists can be Medical Doctors (M.D.) or Doctors of Osteopathy (D.O.). An Ophthalmologist's scope of duties may include: treating eye diseases and injuries, performing surgery, prescribing medications, performing vision examinations and fitting contact lenses.
An Optician can fill a doctor's eyewear prescription, expertly fit and adjust eyeglasses, and in some states, fit and fill a prescription for contact lenses as well. Most opticians work within an "Optical Dispensary," a business which engages in the sale of prescriptive eyeglasses, contact lenses, and non-prescriptive ophthalmic products.
Types of Prescription Eyeglass Lenses
Based upon the specific eyesight disorder, various types of corrective lenses are prescribed. As a rule, there are four types: Single Vision, Bifocal, Trifocal, and Progressive.
Single Vision lenses have one viewing area throughout the lens. This corrected area can be for distance, near distance, or reading.
Bifocals (meaning a lens with two points of focus, usually one for distance and one for close-up vision) are some of the most commonly prescribed multi-focal lenses. A small portion of the bifocal lens is reserved for the near-vision correction. The rest of the lens is usually a distance correction, but may have no correction at all if the wearer has good distance vision.
Trifocal lenses have three points of focus: usually for distance, intermediate and close-up vision. Trifocals have an added "segment" area above the bifocal for viewing objects in the intermediate zone: about an arm's length away. Computer screens are typically in the intermediate zone.
Progressive ("no-line") lenses correct vision for multiple distances without the visible "segment" lines of bifocal or trifocal lenses. Instead, these lenses have a graduated section in which the power of the lens progresses smoothly from one prescription to the next, letting the wearer see clearly at virtually all distances.
Lenticular lenses are used to correct extreme cases of farsightedness when lens implants are not practical. This type of farsightedness (hyperopia) can be a result of cataract surgery. A similar type of lens, called the myodisc or "minus lenticular" lens, is used to correct extreme cases of nearsightedness. The lenticular lens is sometimes said to resemble a "fried egg"; that is, a hemisphere on top of a flat surface. This is because the power of the lens is concentrated into a small area in the lens' center to avoid the great thickness and weight that would result if the power were distributed throughout the lens. The rest of the lens has little or no power and is present simply to support the center lenticular portion.
Eyeglass Lens Material Types
Choosing the right lens material is important, and there are several options:
Accounting for nearly 50% of all lenses sold in the U.S., plastic is the most popular of all lens materials. Plastic offers good optical clarity at a lower price point, but because it's generally thicker than glass at various powers, it is not typically recommended for higher prescriptions.
Polycarbonate are the most durable of all lenses. They're over ten times more impact resistant than regular plastic. They are also one of the lightest, thinnest lens materials used in eyewear (up to 40% thinner and 30% lighter than standard plastic lenses). Polycarbonate remains a good choice for those who want the safest and/or lightest lenses possible. It is also an excellent material choice for children's glasses.
Hi Index lenses are an excellent alternative for patients with higher prescriptions that want the thinnest, most attractive lenses possible. Hi Index lenses range from 20% to 65% thinner than plastic lenses (depending on the refractive index). The higher the refractive index, the thinner the lens (and typically the higher the cost).
Photochromic lenses are optical lenses that darken on exposure to specific types of light of sufficient intensity, most commonly ultraviolet (UV) radiation. In the absence of activating light the lenses return to their clear state. Photochromic lenses may be made of glass, polycarbonate, or another plastic.
Polarized lenses specialized eyewear designed to reduce glare from surfaces such as water, snow, and glass. Polarized lenses are available in a variety of colors, depending on the material from which the lenses are made.
The Trivex lens is a lightweight, impact resistant material much like polycarbonate. It offers the added benefits of lower visual distortion, better optics, and built-in U.V. Protection. Trivex is preferred over polycarbonate lenses in prescription sunglasses because it can be more easily tinted.
Contact Lens Fitting
When patients prefer contact lenses instead of eyeglasses, additional evaluation is typically required to find the right type and size of contact lens. This additional evaluation is commonly referred to as a "contact lens fitting." Most providers charge an additional fee for this type of fitting and the fee will vary depending on the provider. The cost may also vary due to circumstances or complexities involving condition of the eyes and cornea, the lens prescription and the type of lenses used.
The first step in contact lens fitting involves measuring the patient's eye to determine the correct size of the contact lens. In the case of disposable contact lenses, "trial" lenses may be issued so that the fit can be evaluated. Patients new to contact lens wear will be instructed on proper cleaning, insertion and removal of the lenses. A wear schedule may be prescribed to allow the patient to adapt gradually to the lenses, leaving them in for longer periods each day. The Doctor may carefully monitor the eyes over a specified period of time to determine a proper fit and to ensure that there are no complications.
There are generally two categories of contact lens patients: (1) Elective/Cosmetic and (2) Medically Necessary.
Most contact lens wearers fall under the "elective/cosmetic" category. These patients have chosen to wear contact lenses for cosmetic, fashion or vocational reasons.
Some patients cannot achieve clear, comfortable vision with eyeglasses due to certain medical conditions. Medical conditions that may make these lenses necessary include: Keratoconus, Anisometropia, Aphakia and Pseudophakia. (Prior Approval is required to authorize medically necessary contact lenses).
Types of Prescription Contact Lenses
Contact lenses have been traditionally categorized by their material type: being either "Soft", "Rigid Gas Permeable (RGP)" or "Hard" lenses ("Hard" lenses are virtually obsolete and rarely used). In addition to being categorized by material, contact lenses may also be identified by their wearing characteristics (daily-wear, disposable, planned replacement, etc.) and according to the type of prescription (toric, bifocal, monovision etc.). The following terms are generally used in describing the various types of contact lenses.
"Daily-wear" soft contact lenses
These lenses are made of flexible, soft plastics that allow oxygen to pass through to the eye. They are easy to adjust to and comfortable to wear. Because they fit close to the eye and are difficult to dislodge, they are often recommended for sports. They won't correct all vision problems, however, and may not provide the sharp vision required by some wearers. They also require daily removal and cleaning.
Disposable soft lenses are normally worn for one or two weeks and then discarded. They are easy to adjust to and comfortable to wear. Because they fit close to the eye and are more difficult to dislodge, they, too, are often recommended for sports. As with the "daily-wear" lenses, they won't correct all vision problems and may not provide the level of vision required by some wearers. They also require daily removal and cleaning, but need much less maintenance than standard daily-wear soft contact lenses.
This type of disposable lens is designed to be worn for a single day, discarded at night, and replaced by a new pair in the morning. The big advantages are that no lens care is needed and a fresh pair of lenses is worn every day.
These contact lenses are replaced on a planned schedule, usually monthly or quarterly. They are available for most prescriptions and require less care than standard daily-wear contact lenses, since they are frequently replaced.
These contact lenses can usually be worn for a specified number of days (overnight) without removal. Because of the "extended" wear time, more frequent visits to the eye doctor for follow-up care may be required. "Continuous wear" is a term that's sometimes used to describe 30 consecutive nights of extended lens wear - the maximum wearing time approved by the FDA.
Gas permeable (RGP) contact lenses
RGP contact lenses are manufactured from slightly flexible plastics that allow oxygen to pass through. These lenses may provide sharper vision than standard soft lenses and can be used to correct most vision problems. They are also more durable and easier to care for, but often require a considerably longer period of adjustment.
Contact lenses that contain both a spherical and cylinder component to correct prescriptions in patients who have astigmatism. These lenses may be thicker in one area than another to maintain correct orientation on the eye.
As with multifocal eyeglasses, bifocal contact lenses are designed to provide sharp vision up close and at a distance. Various designs are available depending on the specific needs and adaptability of the patient.
Monovision is a contact lens fitting technique that is an alternative to bifocal contacts. Using this technique, the eye doctor fits a close-up prescription contact in one eye for reading and a distance vision contact in the other. The technique can be very effective for some patients, but requires some adaptation and sometimes results in compromised depth perception. Monovision fitting can be performed with virtually any type of standard or specialty contact lens.