Evaluation of the Ophthalmologic Patient

The first step in an ophthalmologic evaluation is to record visual acuity. Many patients do not give a full effort. Providing adequate time and coaxing patients tend to yield more accurate results. Visual acuity is measured with and without the patient's own glasses. If patients do not have their glasses, a pinhole refractor is used. If a commercial pinhole refractor is unavailable, one can be made at the bedside by poking holes through a piece of cardboard using an 18-gauge needle and varying the diameter of each hole slightly. Patients choose the hole that corrects vision the most. If acuity corrects with pinhole refraction, the problem is a refractive error. Pinhole refraction is a rapid, efficient way to diagnose refractive errors, which are the most common cause of blurred vision. However, with pinhole refraction, best correction is usually to only about 20/30, not 20/20.

Visual acuity in each eye is tested as the opposite eye is covered with a solid object (not the patient's fingers, which may separate during testing). Patients look at an eye chart 20 ft (6 m) away. If this test cannot be done, acuity can be measured by using a chart held about 36 cm (14 in) from the eye. Normal and abnormal vision is quantified by Snellen notation. A Snellen notation of 20/40 (6/12) indicates that the smallest letter that can be read by someone with normal vision at 40 ft (12 m) has to be brought to 20 ft (6 m) before it is recognized by the patient. Vision is recorded as the smallest line in which the patient can read half of the letters, even if the patient feels that the letters are blurry or they have to guess. If the patient cannot read the top line of the Snellen chart at 20 ft (6 m), acuity is tested at 10 ft (3 m). If nothing can be read from a chart even at the closest distance, the examiner holds up different numbers of fingers to see whether the patient can accurately count them. If not, the examiner tests whether the patient can perceive hand motion. If not, a light is shined into the eye to see whether light is perceived.

Near vision is checked by asking patients to read a standard near card or newsprint at 14 in (36 cm); patients > 40 years who require corrective lenses (reading glasses) should wear them during near vision testing.

Refractive error can be estimated roughly with a handheld ophthalmoscope by noting the lens necessary for the examiner to focus on the retina; this procedure requires examiners to use their own corrective lenses and is never a substitute for a comprehensive assessment of refraction. More commonly, refractive error is measured with a standard phoropter or an automated refractor (a device that measures changes in light projected and reflected by the patient’s eye). These devices also measure astigmatism (see Overview of Refractive Error).

Eyelid margins and periocular cutaneous tissues are examined under a focal light and magnification (eg, provided by loupe, slit lamp, or ophthalmoscope). In cases of suspected dacryocystitis or canaliculitis, the lacrimal sacs are palpated and an attempt is made to express any contents through the canaliculi and puncta. After eyelid eversion, the palpebral and bulbar conjunctivae and the fornices can be inspected for foreign bodies, signs of inflammation (eg, follicular hypertrophy, exudate, hyperemia, edema), or other abnormalities.

The size and shape of the pupils are noted, and pupillary reaction to light is tested in each eye, one at a time, while the patient looks in the distance. Then the swinging flashlight test is done with a penlight to compare direct and consensual pupillary response. There are 3 steps:

1. One pupil is maximally constricted by being exposed to light from the penlight for 1 to 3 seconds.

2. The penlight is rapidly moved to the other eye for 1 to 3 seconds.

3. The light is moved back to the first eye.

Normally, a pupil constricts similarly when light is shined on it (direct response) and when light is shined on the other eye (consensual response). However, if one eye has less light perception than the other, as caused by dysfunction of the afferent limb (from the optic nerve to the optic chiasm) or extensive retinal disease, then the consensual response in the affected eye is stronger than the direct response. Thus, on step 3 of the swinging light test, when the light is shined back on the affected eye, it paradoxically appears to dilate. This finding indicates a relative afferent pupillary defect (RAPD, or Marcus Gunn pupil).

The examiner guides the patient to look in 8 directions (up, up and right, right, down and right, down, down and left, left, left and up) with a moving finger, penlight, or transillumination light, observing for gaze deviation, limitation of movement, disconjugate gaze, or a combination consistent with cranial nerve palsy, orbital disease, or other abnormalities that restrict movement.

Ophthalmoscopy (examination of the posterior segment of the eye) can be done directly by using a handheld ophthalmoscope or with a handheld lens in conjunction with the slit lamp biomicroscope. Indirect ophthalmoscopy can be done by using a head-mounted ophthalmoscope with a handheld lens. With handheld ophthalmoscopy, the examiner dials the ophthalmoscope to zero diopters, then increases or decreases the setting until the fundus comes into focus. The view of the retina is limited with a handheld ophthalmoscope, whereas indirect ophthalmoscopy gives a 3-dimensional view and is better for visualizing the peripheral retina, where retinal detachment most commonly occurs.

The view of the fundus can be improved by dilating the pupils. Before dilation, the anterior chamber depth is estimated because mydriasis can precipitate an attack of acute angle-closure glaucoma if the anterior chamber is shallow. Depth can be estimated with a slit lamp or less accurately with a penlight held at the temporal limbus parallel to the plane of the iris and pointed toward the nose. If the medial iris is in shadow, the chamber is shallow and dilation should be avoided. Other contraindications to dilation include head trauma, suspicion of a ruptured globe, a narrow angle, and angle-closure glaucoma.

Ophthalmoscopy can detect lens or vitreous opacities, assess the optic cup-to-disk ratio, and identify retinal and vascular changes. The optic cup is the central depression, and the optic disk is the entire area of the optic nerve head. The normal ratio of the cup-to-nerve diameters is 0 to 0.4. A ratio of ≥ 0.5 may signify loss of ganglion cells and may be a sign of glaucoma.

Retinal changes include

• Hemorrhage, manifested as small or large areas of blood

• Drusen (small subretinal yellow-white spots that may signify dry age-related macular degeneration)

Vascular changes include

• Arteriovenous nicking, a sign of chronic hypertension in which retinal veins are compressed by arteries where the two cross

• Silver wiring, a sign of hypertension in which thin, fibrotic arteriolar walls decrease the thickness of the light reflex

• Loss of venous pulsations, a sign of increased intracranial pressure in patients known to have had pulsations

A slit lamp focuses the height and width of a beam of light for a precise stereoscopic view of the eyelids, conjunctiva, cornea, anterior chamber, iris, lens, and anterior vitreous. With a handheld condensing lens, it can also be used for detailed examination of the retina and macula. It is especially useful for the following:

• Identifying corneal foreign bodies, abrasions, and other corneal disorders

• Measuring depth of the anterior chamber

• Detecting cells (RBCs or WBCs) and flare (evidence of protein) in the anterior chamber

• Identifying the location and degree of lens opacities (cataracts)

• Identifying diseases such as macular degeneration, diabetic eye disease, epiretinal membranes, macular edema, and retinal tears (when using a condensing lens)

Tonometry and gonioscopy, which quantifies the iridocorneal angle and requires the use of a special lens, may be done.

Visual fields may be impaired by lesions anywhere in the neural visual pathways from the optic nerves to the occipital lobes (see table Types of Field Defects and see figure Higher visual pathways). Glaucoma causes loss of peripheral vision. Fields can be assessed grossly by direct confrontation testing or by more precise, more detailed testing.

In direct confrontation, patients maintain a fixed gaze at the examiner’s eye or nose. The examiner brings a small target (eg, a match or a finger) from the patients’ visual periphery into each of the 4 visual quadrants and asks patients to indicate when they first see the object. Slowly wiggling the small target helps patients separate and define it. Another method of direct confrontation visual field testing is to hold a number of fingers in each quadrant and ask patients how many they see. For both methods, each eye is tested separately. Abnormalities in target detection should prompt detailed testing with more precise instruments.

More detailed methods include use of a tangent screen, Goldmann perimeter, or computerized automated perimetry (in which the visual field is mapped out in detail based on patient response to a series of flashing lights in different locations controlled by a standardized computer program). The Amsler grid is used to test central vision. Distortion of the grid (metamorphopsia) or a missing area (central scotoma) may indicate disease of the macula (eg, choroidal neovascularization), as occurs in age-related macular degeneration.

Twelve to 24 Ishihara color plates, which have colored numbers or symbols hidden in a field of colored dots, are commonly used to test color vision. Color-blind patients or patients with acquired color deficiency (eg, in optic nerve diseases) cannot see some or all of the hidden numbers. Most congenital color blindness is red-green; most acquired (eg, caused by glaucoma or optic nerve disease) is blue-yellow.

glaucoma; the optic nerve also should be examined.

age-related macular degeneration.

Optical coherence tomography (OCT) provides high-resolution images of posterior eye structures, such as the retina (including retinal pigment epithelium), choroid, posterior vitreous, and optic nerve. Retinal edema can be identified. OCT works in a manner similar to that of ultrasonography but uses light instead of sound; it does not involve contrast use or ionizing radiation and is noninvasive. OCT is useful in imaging retinal disorders that cause macular edema or fibrous proliferation over or underneath the macula, including age-related macular degeneration, diabetic retinopathy, macular holes, and epiretinal membranes. It is also useful for monitoring progression of glaucoma and other optic nerve abnormalities.

Electrodes are placed on each cornea and on the surrounding skin, and electrical activity in the retina is recorded. This technique evaluates retinal function in patients with retinal degeneration. It does not evaluate vision.

B-mode ultrasonography provides 2-dimensional structural information even in the presence of opacities of the cornea and lens that can interfere with direct examination (eg, with ophthalmoscopy). Examples of ophthalmologic applications include assessment of retinal tumors, detachments, and vitreous hemorrhages; location of foreign bodies; detection of posterior scleral edema characteristic of posterior scleritis; and distinction of choroidal melanoma from metastatic carcinoma and subretinal hemorrhage.

A-mode ultrasonography is 1-dimensional ultrasonography used to determine the axial length of the eye, a measurement needed to calculate the power of an intraocular lens for implantation as a part of cataract surgery.

Ultrasonic pachymetry is use of ultrasonography to measure the thickness of the cornea before refractive surgery (eg, laser in situ keratomileusis [LASIK]) and in patients with corneal dystrophies.

These imaging techniques most often are used for evaluation of ocular trauma, particularly if an intraocular foreign body is suspected, and in the evaluation of orbital tumors, optic neuritis, and optic nerve tumors. MRI should not be done when there is suspicion of a metallic intraocular foreign body.