|
|
|
|
|
||||||||||||||||||||||||||||
|
Case Report This benign condition has many serious masqueraders. For clinicians, it's a diagnosis of exclusion.
by Rodney J. Smith, O.D., Fort Lauderdale, Fla. The parents of an 18-month-old white male presented complaining about the child's nystagmus, which had been present since he was 3-4 weeks old. They thought the nystagmus had
improved slightly since its initial onset. The patient's mother had a normal prenatal history and relatively easy labor. The baby went full-term, weighing 7 pounds, 4 ounces. Apgar scores were not known. They reported the baby
had no health problems, and no history of trauma or surgeries. The patient was taking no medications and had no known drug allergies.
Diagnostic Data The pupils were round, equal (5mm in normal room illumination) and reactive to light (4+), with no evidence of an afferent pupillary defect. Eyes appeared aligned with the alternating cover test at distance and Hirschberg's test at near. Extra-ocular muscles appeared full. Because of the patient's age, I did not attempt color vision, stereo acuity or confrontational fields. The patient had a constant, horizontal, pendular nystagmus of moderate frequency. It was difficult to have him change fixation, but I observed no apparent null point. The nystagmus dampened moderately with convergence, and in-creased moderately on peripheral gaze. There was a positive latent component. Distant non-cycloplegic retinoscopy was -6.25 -0.75 x 070 O.D. and -5.00 -1.00 x 020 O.S. Cycloplegic retinoscopy was -6.00 -1.00 x 070 O.D. and -4.75 -1.50 x 020 O.S. Anterior segment evaluation was unremarkable and showed no ocular pathology. There were no trans-illumination defects of the iris. Posterior segment and peripheral retinal evaluation with both direct and binocular indirect ophthalmoscopy was unremarkable. Diagnosis Treatment and Follow-Up
He returned one year later at age 2 1/2. There was no chief complaint and no change in personal or family medical or ocular history. Entrance testing results at this visit were: near-point of convergence (non-accommodative target), 7cm; distance cover test with correction, orthophoric; and near cover test with current prescription, 3 exophoric. Extraocular muscles were full and smooth. The patient exhibited no stereo acuity with the random dot forms, and monocular color vision was normal with children's color plates. Distance visual acuity with the broken wheel test was 20/50 O.U. Because of the latent component of the nystagmus, I fogged the eye not being tested. I attempted near visual acuity with Lea symbols, but he was too young to respond. The nystagmus was unchanged from the previous exam. I made a small change in the glasses Rx and reemphasized the importance of annual exams. Discussion Strabismus may coexist with congenital nystagmus, and the amount of visual impairment is variable.5 At onset there are wide, swinging eye movements. At age 4-6 months, small pendular eye movements begin, and at 6-12 months, jerk nystagmus and a null point develop. Compensatory head nodding develops at any point up to age 20.8 Nystagmus with abnormal head position and head nodding characterizes spasmus nutans. It develops at 4-12 months, and usually re-solves before age 3. Spasmus nutans is characteristically asymmetrical, pendular, fine and rapid. The nystagmus is generally bilateral, but can be monocular, asymmetric and vary in different gaze positions.2 It is usually horizontal, but may occasionally be vertical or rotary.5 The child in this case had no head nodding or abnormal head posture.
Most techniques to evaluate clinical nystagmus patients are the same as those we use for routine clinical evaluations. A detailed case history is essential. When evaluating visual acuity, have the patient assume his habitual head position, if there is one. Because a latent component may contribute to the nystagmus, assess acuity with a method that doesn't disassociate the eyes, such as a Polaroid slide. Or, as with this patient, use excessive plus power to fog one eye and assess the acuity of the fellow eye. The literature recommends a +5.00D fogging lens.9 Try to correct any significant refractive error, though measuring the error can be challenging. Re-check the refraction on subsequent visits to refine the measurement and monitor changes in a growing child.7 Congenital nystagmus generally is not curable, but it is manageable. Prescription glasses help lessen its effects. Use conservative criteria for prescribing.7 Other treatments include lenses and prisms, contact lenses and vision therapy. Some patients report that contact lenses are of limited value.1 However, some clinicians believe contact lenses are indicated for all children with nystagmus.7 Patients with both nystagmus and high refractive error may obtain poor optical correction with spectacles because the visual axis is intermittently aligned with the lens' optical center, inducing distortion and prismatic effects. A contact lens will move with the visual axis and reduce these effects. There are reports that the weight of spectacle lenses dampen the effect of the nystagmus, and that through sensory feedback, contact lens movement on the eye increases awareness of eye movement. These are anecdotal reports and neither has been confirmed.10 Prisms can be used two different ways to treat congenital nystagmus. Yoked prisms can treat abnormal head posture. And, because congenital nystagmus often lessens on convergence, base-out prism (or added minus lenses) can stimulate convergence. The prism necessary to re-duce the nystagmus and improve acuity varies by case, generally ranging between 6.00D and 20.00D. Minus-added lenses are less effective than base-out prism.11 You can attempt visual therapy procedures to promote fusion and steady fixation, and also include intermittent photic stimulation and auditory biofeedback techniques.7 Ocular muscle surgery may also help in some cases by aligning the eyes and reducing a head turn.2 Congenital nystagmus is a benign condition, but is a diagnosis of exclusion; you must rule out other, more serious conditions. After the final diagnosis, your management goal should be to improve visual acuity and enhance binocularity.
Dr. Smith is an assistant professor at Nova Southeastern University College of Optometry. 1. Rosenbloom AA. Morgan MW. Principles and Practices of Pediatric Optometry. Philadelphia: JB Lippincott, 1990:343-344.
|
| | | | | | | |
