Fibers originating from the nasal neuroreceptor cells decussate in the optic chiasm to the opposite optic tract, whereas the temporal fibers continue in the homolateral optic tract. Considerable evidence exists that the visual cells of the retina, that is, the rods and cones, also serve as light receptors controlling pupillomotor activity. The pupillary light reflex arc begins in the retina ( Figure 58.1). The iris dilator fibers contain α-adrenergic sympathetic receptors that respond to changes in sympathetic tonus and changes in the blood level of circulating catecholamines. The size of the pupil is controlled by the activities of two muscles: the circumferential sphincter muscle found in the margin of the iris, innervated by the parasympathetic nervous system: and the iris dilator muscle, running radially from the iris root to the peripheral border of the sphincter. Record these data so that they are easy to read and recall. Next, look at the amount of pupillary constriction that occurs when the patient is forced to focus on a near object, such as a thumb held 15 to 20 cm above the eyes. Slowly move the light up to the patient's eye level and check the pupillary response to the bright light on each side several times. To assess pupillary size in a darkened room, illuminate the face from below. For the same reasons, try not to startle or touch patients with your hands or instruments, as psychosensory stimulation induces mydriasis, hippus, and relatively hyperactive pupils. Patients should be encouraged to fixate visually on a distant object, because if they inadvertently look at your nose or the flashlight, the attempt to converge will reflexly evoke miosis, and certain signs may be overlooked (e.g., anisocoria, light-near dissociation, or a subtle Marcus Gunn sign. Because these phenomena are best tested with the pupils in a semidilated state, clinical observations should be made in a dimly lighted room. In testing extraocular movements note normal conjugate movements or deviations from normal, including the presence of nystagmus, or lid lag.Ĭlick on the video icon for a review of physical examination techniques used to assess the external eye.Ĭlick on the interactive icon to see changes in the sclera, evaluate pupillary size and response to light, and evaluate extraocular muscles.The examiner first must check the size, shape, equality, and position of the pupils, and their response to a bright light. If one of the muscles is weak or paralyzed, the eye will deviate from its normal position. There are six cardinal directions that allow you to test the function of each muscle and the supplying nerve. Normally, the eyes move together and are controlled by six muscles (four rectus and two obliques). If reactivity still seems impaired, test pupillary near reaction. If reactivity seems impaired, be sure that the room has been fully darkened and a bright light has been used. If this is not the case, you need to decide which is the abnormal pupil. If one or both pupils are particularly large or small, be sure that reactivity to light is normal and symmetric. Pupillary inequality is termed anisocoria. Normal pupillary size is between 3-5 mm with less than 0.5mm size difference between the two. In evaluating the pupils, inspect the size, shape, symmetry and reactivity of the pupils. Also note the symmetry of the palpebral fissures, which provide a clue for evaluating exophthalmos or ptosis. In evaluating the cornea and iris look for opacities of the cornea or lens and for abnormal bowing forward of the iris. In evaluating the conjunctiva and sclera, note the color of the palpebral conjunctiva (looking for unusual paleness signifying anemia), the color of the sclera (noting blueness, yellowness, redness), the vascular pattern, or the presence of nodules. To evaluate position, inspect for outward deviation, called exophthalmos. If the reflex on one eye is more medial, the patient may have exotropia if more lateral, the patient may have esotropia. The normal reflection should be symmetric. In evaluating alignment, shine a light into the eyes and evaluate the reflection of light on the pupil or iris. Alignment, position of the eyes, the conjunctiva, and sclera: ![]() Examination of the external eye includes inspection of the alignment and position of the eyes, and evaluation of surrounding structures, conjunctiva, sclera, cornea, iris, pupils and extraocular movements.
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