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.
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.
Mary Bekker, The Gale Group Inc., Gale, Detroit,