An hour behind schedule, the waiting room is packed with anxious patients, and the physician is not in the best mood. Your current patient may have glaucoma. You ask yourself,

Should I perform a visual field test? Do I need to refract?
Should I dilate the pupil? Should I just go ask the doctor?

The role of the ophthalmic technician has grown along with the many new technologies. You distinguish yourself not only by knowing how to perform the various diagnostic tests but also by knowing why and when to perform them.

You, the technician, are the first clinical person with whom the patient has contact; hence, the patient's entire first impression of the office is based upon this experience. You serve as the gateway to effective and efficient doctorpatient relationships. An efficient technician provides clear and accurate information to support the physician's assessment, diagnosis, and treatment of the patient. To do this well, you must know more than the “how to” but also the “why to.”

VISION ASSESSMENT

Typically, the patient is unaware that he or she has glaucoma until after he or she experiences a serious loss of vision. This is the very reason that a careful assessment of visual acuity should take place at each visit.

Never assume binocularity. Each eye must be tested separately.

Make certain that the occluded eye is completely covered, and be sure to tell the patient he or she must not press on that eye. Patients do not realize this causes blurriness (Figure 1).

Ensure that the patient wears his or her distance glasses for the Snellen chart and near spectacles for the Rosenbaum near vision assessment.

The visual field test (perimetry) detects the loss of both peripheral and central vision and, in some cases, can indicate glaucomatous optic nerve damage.1 To manage the glaucoma patient, the visual field test is typically performed every 3 to 6 months. An invaluable technician reviews a patient's chart to guarantee the timing of this practice.

A quick field screening tool is the confrontation field test. This is a crude test performed simply by having the patient look straight ahead and count the examiner's fingers held within the periphery of the patient's field of view. In working with innumerable glaucoma specialists, I found it highly advantageous to ask each physician for his or her own test selection criteria. For example, you may find one physician prefers a 24-2 testing strategy for every patient, no matter what. Another may prefer 24-2 for all patients with a visual acuity of 20/200 or better but a 10-2 for patients with central islands or a visual acuity of 20/400 or worse. Kinetic visual fields may be helpful for observing patients with poor vision as well. Why not make your work go more smoothly by noting these preferences?

REFRACTION AND LENSOMETRY

The Mayo Clinic has reported that both nearsighted and farsighted patients are at higher risk for glaucoma. For the farsighted, they report an increased risk of developing narrow-angle glaucoma and/or angle-closure glaucoma.3 The following glaucoma surgeries can also cause changes in refractive error, specifically, an induction of astigmatism:

  • trabeculectomy
  • canaloplasty
  • deep sclerectomy4

Check patients' eye glasses at every visit, the exception's being the postoperative patient.

Be advised that it is not unusual for glaucoma patients with poor vision to have several different pairs of glasses. They often bring one pair of spectacles for one visit and a different pair for a subsequent visit! This is another reason why you should perform lensometry at each visit.

PUPILARY EVALUATION

A pupillary assessment can produce extremely significant clinical findings. Glaucoma, for instance, can cause pupillary abnormalities such as a relative afferent pupillary defect. The pupil's size, shape, and function can be indicators of related neurological (cranial nerve) function. Note that pupillary size, iris color, and refractive error can vary with age. Some causes of pupillary dilation include

  • acute glaucoma attack (middilated and fixed pupil)
  • retinal disease
  • cranial nerve III palsy (consensual reflex absent)
  • cyloplegia (2º to eyedrops)5

Constricted pupils can be caused by the glaucoma medication pilocarpine.

Swinging Flashlight Test
Pupillary reaction to light is tested for each eye, one eye at a time. The direct and consensual pupillary reaction to light at near and distance are measured and noted along with the pupil's size and shape. Testing the afferent sensory stimulus pathway from eye to brain helps the physician determine whether the cause of the patient's reduced vision is ocular disease. An abnormal result indicates a relative afferent pupillary defect (Figure 2).

Procedure
To perform the procedure:

  • Check the patient's left eye
  • Shine the light onto the left eye and check for pupillary constriction of the left eye (direct)
  • Shine the light onto the left eye and check for pupillary constriction of the right eye (consensual)
  • Check the right eye
  • Shine the light onto the right eye and check for pupillary constriction of the right eye (direct)
  • Shine the light onto the right eye and check for pupillary constriction of the left eye (consensual)

RELATIVE AFFERENT PUPILARY DEFECT

Typically, both pupils should constrict when light is shone into either eye. An injury to the optic nerve, however, can decrease the amount of light ultimately transmitted to the brain, thus decreasing the pupil's normal reaction to the light. A typical result is dilation of the pupil rather than constriction.6 For example, in Figure 3, the left pupil dilates with light. This can indicate a left optic nerve lesion, which will ultimately result in the attenuation of the light signal to the brain.

OCULAR MOTILITY AND ALIGNMENT

Performing tests of ocular motility and alignment can be useful in the detection of potential ocular health problems (Figure 4). By observing how the eyes move when covered and uncovered, the physician can observe proper ocular alignment and how well the eyes move together. Problems with eye movement can be indicative of a large number of troubles—neurologic, ocular, and/or systemic.

Movement of the eyes is measured in all nine positions of gaze:

  • primary
  • up, down
  • left, right
  • four corners (up + right, up + left, down + right, down + left)

Eye movements are tested individually (ductions) and together (versions).

COVER AND UNCOVER TEST

To perform the test, place the occluder over the right eye (Figure 5). Then, uncover and evaluate the eye for movement. Repeat for the left eye.

This test evaluates the patient for the presence of a phoria, a muscular imbalance or an ocular misalignment that only occurs some of the time. The goal is to disrupt fusion of the eyes and to observe the direction in which the covered eye moves.

ALTERNATIVE COVER TEST

This test evaluates the patient for the presence of tropia, a misalignment that is always present. The test is performed after the cover test. Cover the right eye, and then switch to cover the left eye. Now, repeat by moving the cover from the left eye to the right (Figure 6).

HIRSHBERG TEST

The Hirshberg test gives a rough estimate of any ocular deviation (Figure 7). A light is shone onto the patient's eyes while he or she fixates on a distant target. The location of the light reflex relative to the pupil should be noted. The light reflex may be on the nasal edge of the pupil (eso), the temporal edge (exo), or central (ortho).

KRIMSKY TEST

The Krimsky test also assesses the binocular alignment of the patient's eyes (Figure 8). The test is performed in the same way as the Hirshberg test but situates prisms of different strength in front of the eye in such a way as to center the light reflex inside the pupil.

INTRAOCULAR PRESSURE MEASUREMENT

Applanation Tonometry

During a glaucoma evaluation, one of the most important measurements a technician makes is applanation tonometry. The Goldmann applanation tonometer is the gold standard for intraocular pressure (IOP) measurements and provides acceptable accuracy for most patients. The Goldmann tonometer measures a 3.06-mm-diameter area on the cornea. Correct endpoint mire alignment is seen when the two inner margins of the semicircles just touch (Figure 9).

Mire Patterns
Few things frustrate the physician more than inaccurate IOP measurements taken by the technical staff. Equipment lacking calibration can lead to an inaccurate reading. To ensure quality control and minimize factors in incorrect measurements, do the following:

  • Check the tonometer's calibration at least once a month (a must).
  • Inspect the tonometer prism for scratches or signs of degradation (Figure 10).
  • Become familiar with the slit lamp. Different models function differently. You should be comfortable with the movement of the slit lamp prior to performing applanation tonometry.
  • Improve your applanation technique and work on corneal centering.
  • Question differences of more than 3 mm Hg between a patient's two eyes. This is a red flag. Possible causes include poor technique, glaucoma, and uveitis, among others.
  • Ensure that the patient's eye is in the primary position.
  • Note the presence of any venous pulsations observed during applanation.
  • Do not put any pressure on the globe when checking the IOP. Pressure on the globe will raise the patient's IOP. Lids and eyelashes should not touch the tonometer's head.
  • Instruct patients to breathe normally and not to hold their breath, which can alter IOP
  • Ask men wearing neckties or with tight collars to loosen them prior to tonometry, because constriction can alter IOP.
  • Instruct patients who have difficulty getting their chin into the chin rest cup to move to the edge of the chair so that they are not leaning so far forward.
  • Account for corneal astigmatism. Regular astigmatism of greater than 3.00 D may result in an underestimation of IOP in eyes that have with-the-rule astigmatism and an overestimation of IOP in eyes with against-the-rule astigmatism. Rotate the tonometer prism so that the red line of the prism lines up with the axis of the flattest meridian (in minus cylinder).

Corneal irregularities/scarring may cause errors due to difficulty in endpoint determination.

CORNEAL PACHYMETRY

Corneal pachymetry is the measurement of corneal thickness (Figure 11). It has been used to evaluate people with corneal disease and aids in the assessment of individuals at risk for glaucoma.9 Studies have shown that corneal thickness can alter the accuracy of IOP measurements.10 For patients with thick corneas, the actual IOP may be overestimated. For those with thin corneas, the actual IOP may be underestimated. Since the procedure is noninvasive and painless, you can perform it with ease using a topical local anesthetic. With this measurement, you can develop a better appreciation of the relationship between elevated IOP measurements and corneal thickness.

SLIT-LAMP EXAMINATION

The slit lamp provides a three-dimensional view of the structures in the eye. It is used to examine the front (anterior) portion of the eye. This allows the physician to make a careful observation of the orbits, lids, conjunctiva, cornea, anterior chamber, and iris. The angle of aqueous drainage at the peripheral edge of the iris should also be measured.

Two methods of determining the draining angle are

  • flashlight test
  • Van Herrick test

Flashlight Test<

In the flashlight test, a light is shone from the temporal side onto the cornea along an angle parallel to the iris. A shadow on the nasal limbus will identify an eye with a shallow anterior chamber (Figure 12).

Van Herrick Test

The Van Herrick test uses a slit beam to compare the depth of the peripheral anterior chamber to the thickness of the cornea.

When the depth of the peripheral anterior chamber is less than one-quarter of the corneal thickness, it is considered shallow. If the anterior chamber depth is as deep as the cornea is thick, then the angle is presumed to be wide open. If only a slit of aqueous is visible, then the angle is estimated to be dangerously narrow (Figure 13).

How Is the Test Performed?

The slit-lamp settings are as follows:

  • 60º angle
  • narrow beam
  • right beam
  • magnification of 16×

slit beam is very bright and thin, and it is offset 60º temporally to the slit-lamp oculars.

The temporal sclera is illuminated, and the slit lamp beam is brought slowly toward the cornea until the anterior chamber is first identified. Here, the thickness of the cornea is compared to the depth of the peripheral anterior chamber.

If the anterior chamber is as deep as the cornea is thick, then the angle is presumed to be wide open. If there is only a slit of aqueous, then the angle is estimated to be dangerously narrow.

None of the aforementioned tests is a definitive determination of suspected occludable angles and, therefore, should not be used as a replacement for gonioscopy. They are, however, means of confirming what the gonioscopic examination reveals.

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