Eye Examination

Definition

An eye examination is a series of tests performed by an ophthalmologist or an optometrist to determine if there are any pre-existing or potential problems with a patient's vision.

Purpose

Eye examinations measure a person's ocular health and visual status, in order to detect abnormalities in the components of the visual system, and to determine how well the person can see. Eye exams may also reveal the presence of non-eye diseases such as high blood pressure or diabetes.

Infants should be examined to detect any physical abnormalities. If a problem is noted the infant can be further examined, generally by a pediatric ophthalmologist. A child without symptoms should have an eye exam before age three. Early exams are important because some conditions may result in permanent problems with vision. For example, amblyopia, more commonly known as a lazy eye, should be corrected before permanent damage occurs, usually between the ages of six and nine. If a child continues to be symptom-free, the second exam should take place before first grade. After first grade, the American Optometric Association recommends an eye exam every two years until age 19. From ages 19-40, an examination every two to three years is recommended, and from ages 41-60, an exam every two years is recommended. After that, healthy persons without risk factors are recommended to have annual examinations. Doctors should advise patients at risk for eye disease that they may need more frequent checkups. Persons with visual problems should seek medical attention right away.

Precautions

The examiner, who may be an O.D., D.O., M.D., ophthalmic nurse, ophthalmic assistant, or ophthalmic technician, should log any medications the patient is taking and any existing health conditions. Some medications can affect vision or interfere with the eyedrops used during the exam. Certain types of eyedrops should not be prescribed if the patient has asthma, heart problems, or other conditions.

The patient may need transportation if the eyes are dilated. Physicians may advise patients to wear dark glasses to decrease the glare from strong light until the effects of the medication are sufficiently diminished.

Description

An eye examination is performed by an optometrist (who has an O.D. degree) or an ophthalmologist. Ophthamologists either have a M.D. or a D.O. (doctor of osteopathy) degree. An eye examination, given by an ophthalmologist or optometrist with assistance from ophthalmic nurses, assistants and technicians, costs about $100 and may or may not be covered by insurance. It begins with a patient history and continues with a series of primary tests. Additional specialized tests are administered as needed. The primary tests can be divided into two groups: those that evaluate the physical state of the eyes and surrounding areas; and those that measure the ability to see. Some variation exists, but most eye examiners and their assistants take a patient history and perform a standard set of primary tests.

Patient history and initial observations

The ophthalmic nurse, assistant, or technician will take eye and medical histories that include the patient's chief complaint, any past eye disorders, current medications, any family history of eye disorders, and any systemic disorders the patient may have. Sample questions may include "How is your vision?" or "Do you have any allergies?" Examiners also should ask about the patient's lifestyle. This information may modify prescriptions. For example, a construction worker needs protective eyewear. Patients should be encouraged to bring all of their currently used corrective lenses to the exam (contacts and glasses). This allows the ophthalmic staff to determine the prescription using a lensometer, and allows the examiner to determine the efficacy of the current prescription.

Visual acuity tests

Visual acuity measures how clearly the patient can see. The examiner measures each eye separately, with and without the current prescription. Examiners use a Snellen eye chart with lines of different-sized letters. Each line has a number at the side denoting the distance from which a person with normal vision can read that line. Other charts are available for children or anyone unfamiliar with the Roman alphabet. Charts should be placed at the recommended distance (usually 20 feet, or 6 m) from the patient. At that distance, persons with normal vision can read the line marked 20/20, and are said to have 20/20 vision. Patients who cannot read that line are assigned a ratio based on the smallest line they can read. The first number (numerator) of the ratio is the distance between the chart and the patient, and the second number (denominator) is the distance where a person with normal vision would be able to read that line. The ratio 20/40 means the patient sees at 20 feet what people with normal vision can see at 40 feet.

When a patient is unable to read any of the lines, the patient is moved closer until the line with the largest letters is readable. A ratio of 5/200 means the person being tested can see at five feet (1.8.m) what a normal person can see at 200 feet (60 m).

If a patient can't read the chart at all, the examiner may hold up fingers and ask the patient to count them at various distances. The examiner records the result as "counting fingers" at the distance of recognition. If the patient cannot count the fingers at any distance, the examiner determines if the patient can see hand movements. If so, the result is recorded as "hand movements." If not, the examiner determines if the patient can detect light from a penlight. Detection of light and its direction is recorded as "light projection." If the patient can detect the light but not its direction, the result is recorded as "light perception." If the patient cannot detect the light at all, the result is recorded as "no light perception."

Eye movement examination

The examiner asks the patient to follow an object (often the examiner's finger) left, right, up, down, and in all four diagonal directions in order to ensure that the eyes are capable of the full range of motion and that the motions are smooth. Next is a peripheral visual field test. The examiner asks the patient to stare at an object, then quickly covers one eye and notes any movement in the eye that remains uncovered. This procedure is repeated with the other eye. This, and another similar test, helps detect an eye turn or problem with fixation. The examiner may also have the patient look at a pen and follow it as it is moved close to the eyes to check convergence.

Iris and pupil examination

The doctor or assistant checks the pupil's response to light and accommodation (whether it dilates and constricts appropriately). The iris is viewed for symmetry and overall physical appearance. The iris is checked more thoroughly during the slit lamp examination.

Refraction examination

If a patient has visual acuity less than 20/20, the examiner will determine the refractive error and prescribe corrective lenses. To determine refractive error, the examiner utilizes a phoropter. A phoropter is an instrument equipped with many lenses. The examiner uses them to test many combinations of corrections in order to learn which correction allows the patient to see the eye chart most clearly. The phoropter also contains prisms, and sometimes the examiner will intentionally make the patient see double. This maneuver may help in determining a slight eye turn, as well as comparing the acuity of the right and left eye. The exam assesses far (distance) vision and near (reading) vision.

Examiners can also determine a lens prescription by utilizing an automated refracting device. The device measures the necessary refraction by shining a light into the eye and scanning the reflected light. Another way to obtain a prescription is using a hand-held retinoscope. As in the automated method just mentioned, the doctor shines a light in the patient's eyes and can determine an objective prescription. This is helpful in young children or infants.

Physicians or assistants may instill eyedrops in the patient's eyes before refraction. The drops relax accommodation so that the refraction is more accurate. This is helpful in children and people who are farsighted.

Ophthalmoscopic examination

These observations are best accomplished after dilating the pupils and require an ophthalmoscope. The ophthalmoscope most frequently used is a called a direct ophthalmoscope. It is a hand-held illuminated 15X multi-lens magnifier that allows the examiner to view the back of the inside area of the eye (the fundus). The retina, blood vessels, optic nerve, and other structures are examined.

Slit lamp examination

The slit lamp (biomicroscope) is a microscope with an adjustable light source. This instrument magnifies and illuminates the external structures of the eyes. The lid and lid margin, cornea, iris, pupil, conjunctiva, sclera, and lens are examined. The slit lamp is also used in contact lens evaluations. With the use of a condensing lens, the biomicroscope provides an excellent view of the internal structures of the eye.

Visual field measurement

A perimeter, an instrument for measuring visual fields, is a hollow hemisphere equipped with a light source that projects dots of light over the inside surface of the hemisphere. The patient's head is positioned so that the eye being tested is at the center of the sphere and 33 cm (about 13 in) from all points on the hemisphere's inside surface. The patient stares straight ahead at an image on the center of the surface of the perimeter, and signals whenever they detect a light with their peripheral, or side, vision. The perimeter records whether flashes are seen or missed and maps the patient's field of vision.

Intraocular pressure (IOP) measurement

Small probes called tonometers are used to measure IOP. Contact tonometers contact the eyeball directly. A colored anesthetic eyedrop is usually instilled immediately before this test. Other tonometers (noncontact tonometers) measure pressure by expelling a puff of air toward the eyeball from a very short distance. The noncontact tonometers are often not as accurate as the contact tonometers.

Additional tests

In addition to the primary tests already described, the examiner should observe the general health of the eye and structures around it. Depending upon the results of all the primary tests, other tests may also be necessary. These can include, but are not limited to, binocular indirect ophthalmoscopy, gonioscopy, color vision tests, and contrast sensitivity. The patient may have to return for additional visits.

Aftercare

Seeing clearly does not necessarily mean the eyes are healthy. Patients should be advised that regular checkups can detect abnormalities. Patients also should be examined if they notice a change in vision, eyestrain, blur, flashes of light, a sudden onset of floaters, distortion, double vision, redness, pain or discharge.

External observations

INITIAL OBSERVATIONS AND SLIT LAMP EXAM. Some general observations the doctor may be looking for include: head tilt; drooping eyelids; eye turns; red eyes; eye movement; the iris size, shape, and color; clarity of the cornea, anterior chamber, and lens. The anterior chamber lies behind the cornea and in front of the iris. If it appears cloudy or if cells can be seen in it during the slit lamp exam, an inflammation may be present. A narrow anterior chamber may place the patient at risk for glaucoma. Any abnormality indicates a need for medical care.

Internal observations

OPHTHALMOSCOPIC EXAM. The observations include, but are not limited to, the retina, blood vessels, optic nerve, macula, and fovea. The macula is a 0.1-0.2 in (3-5 mm) area of the central retina and is responsible for central vision. The fovea is a small area located within the macula and is responsible for sharp vision. When a person looks at something, they are directing the fovea at the object. Changes in the macular area can be observed with the ophthalmoscope. Retinal tears or detachments can also be seen. An abnormality may indicate a need for medical care.

Visual ability

VISUAL ACUITY. The refraction will determine the refractive status for each eye. Different materials for glasses or contact lenses may be suggested.

KEY TERMS

Amblyopia—Decreased visual acuity, usually in one eye, in the absence of any structural abnormality in the eye.

Conjunctiva—The mucous membrane that covers the white part of the eyes (sclera) and lines the eyelids.

Cornea—Clear outer covering of the front of the eye.

Floaters—Translucent specks that float across the visual field, due to small objects floating in the vitreous humor.

Fundus—In the eye, fundus refers to the back area that can be seen with the ophthalmoscope.

Glaucoma—Glaucoma results in optic nerve damage and a decreased visual field and blindness if not treated. It is usually associated with increased IOP, but that is not always the case. The three factors associated with glaucoma are increased IOP, a change in the optic nerve head, and changes in the visual field.

Gonioscope—An instrument used to inspect the eye (e.g., the anterior chamber). It consists of a magnifier and a lens equipped with mirrors; it's placed on the patient's cornea.

Iris—The colored ring just behind the cornea and in front of the lens that controls the amount of light sent to the retina.

Macula—The central part of the retina where the rods and cones are densest.

Ophthalmoscope—An instrument designed to view structures in the back of the eye.

Optic nerve—The nerve that carries visual messages from the retina to the brain.

Pupil—The circular opening that looks like a black hole in the middle of the iris.

Retina—The inner, light-sensitive layer of the eye containing rods and cones; it transforms the image it receives into electrical messages, which are then sent to the brain via the optic nerve.

Sclera—The tough, fibrous, white outer protective covering that surrounds the eye.

Slit lamp—A microscope that projects a linear slit beam of light onto the eye; it allows viewing of the conjunctiva, cornea, iris, aqueous humor, lens, and eyelid.

Tonometer—An instrument that measures intraocular pressure (IOP).

VISUAL FIELDS. A normal visual field extends about 60° upward, about 75° downward, about 65° toward the nose, and about 100° toward the ear. There is one blind spot close to the center, which corresponds to the area of the optic nerve, which has no light-sensing cells. Defects in the visual field signify damage to the retina, optic nerve, or the neurological visual pathway. An abnormality may indicate a need for medical care.

Results

An eye examination can help maintain or restore clear, comfortable vision. It also aids in disease prevention. After an examination, patients should be more aware of their ocular health and general health.

Health care team roles

Nursing and allied health professionals play an important role in the eye examination and follow-up. Ophthalmic assistants and technicians facilitate the examination by logging the pertinent patient history.

Depending on skill level, ophthalmic assistants may perform measurement of visual acuity under both low and high illumination, assessment of ocular motility and binocularity, and assessment of visual fields and measurement of IOPs with tonometers.

Advanced and intermediate level ophthalmic technicians perform refractions and determine the patient's depth perception. These professionals may also perform corneal topography (mapping).

Some of these professionals seek certification through the American Board of Opticianry/National Contact Lens Examiners and other organizations. These organizations offer seminars and testing that inform professionals of technological advances in refraction and eyeglass manufacturing.