Gunter K. von Noorden

A Reassessment of Infantile Esotropia XLIV Edward Jackson Memorial Lecture

Essential infantile esotropia is an early acquired, not a congenital, condition, although congenital factors may favor its development between the ages of 3 and 6 months. It must be distinguished from other forms of esotropia with an onset between birth and the first six months of life. The cause of essential infantile esotropia remains unknown, but advances in our knowledge can be expected from the rapidly emerging discipline of infant psychophysics. In analyzing treatment results, a clear distinction must be made between normal, subnormal, and anomalous forms of binocular cooperation. While complete restoration of normal binocular function is rarely, if ever, achieved, anomalous binocular cooperation has many functional advantages over suppression or diplopia and should not be disturbed by overzealous treatment. Subnormal binocular vision is considered to be an optimal, microtropia a desirable, and a residual small angle heterotropia an acceptable end stage of surgical therapy. In a study of 358 surgically treated patients with a documented onset of essential infantile esotropia before age 6 months, subnormal binocular vision was present in 71 (20%), a microtropia in 25 (7%), and a small angle esotropia or exotropia in 140 (39%) of the patients. Surgical alignment before completion of the second year of life improved the chances for an optimal treatment result. However, conclusion of surgical treatment after the age of 2 or even 4 years did not preclude the development of binocularity on a subnormal or anomalous basis in many patients.

Apparent foveal displacement in normal subjects and in cyclotropia.

The average location of the fovea in relation to the optic nerve head was determined on fixation photographs from both eyes of 50 non-strabismic subjects. It was found to be 0.3 disc diameters below a horizontal line extended through the geometric center of the optic disc. The range of interocular and inter-individual variations from this position has been described. With the availability of this information, ophthalmoscopy and fundus photography have become useful ancillary tools in the diagnosis of cyclodeviations.

New Clinical Aspects of Stimulus Deprivation Amblyopia

An analysis of clinical data from 11 patients with stimulus deprivation amblyopia showed that amblyopia occurs after monocular visual deprivation that begins between birth and the age of 5¾ years and lasts for one to 36 months. Contrary to previous impressions, stimulus deprivation amblyopia does respond to occlusion therapy of the nondeprived eye. As a rule, improvement in visual acuity can be expected in patients whose visual deprivation began after the age of 30 months. In those patients whose visual deprivation began at birth or during infancy, treatment was unsuccessful when started after the age of 2½ years. However, clinical data from one patient treated successfully during infancy indicated that the deleterious effects of visual deprivation from birth may be preventable.

Behavioral studies of the sensitive periods of development of visual functions in monkeys

The age-dependent effects of monocular form deprivation on psychophysically determined visual functions were investigated in rhesus monkeys. Monocular form deprivation was initiated at various ages from 1 to 25 months and maintained for 18 months. The effects of form deprivation varied across the visual functions evaluated. Absolute scotopic sensitivity was depressed by form deprivation initiated only at 1 or 2 months of age. Photopic, increment-threshold spectral sensitivity functions showed alterations in sensitivity levels for monkeys treated at 5 months of age or earlier, with no effect thereafter. Monocular form deprivation at 1 to 5 months of age resulted in profound deficits in spatial modulation sensitivity. The effects on spatial vision decreased systematically as the age of onset was delayed from age 6 to 18 months. Finally, binocular summation measures revealed an absence of binocular vision even for the monkey form-deprived at 25 months of age, i.e. the experimental treatment series failed to define the upper limit of the age-range for the effects of monocular form deprivation on binocular summation mechanisms. Comparisons of the age-dependent effects of monocular form deprivation across the various functions demonstrated that the sensitive period, i.e. the period of life during which a visual function may be altered by monocular form deprivation, was different for each of the psychophysical measures of visual function.

Imaging of Cerebral Blood Flow and Metabolism in Amblyopia by Positron Emission Tomography

We used positron emission tomography to study monocular visual activation of various brain regions in four amblyopic and two normally sighted adults. Imaging of relative cerebral blood flow using the tracer H2(15)O showed reduced activation of primary visual cortex by the amblyopic as compared with the sound eye. Imaging of relative cerebral glucose metabolism using the tracer [18F]-2-deoxyglucose showed equal activation of primary visual cortex by either eye in the control subject, but reduced activation of primary and accessory visual cortex by the amblyopic as compared with the sound eye in two amblyopic subjects. Relative glucose metabolism was consistently higher in the frontal and temporal lobes contralateral to the viewing eye, both in normal and amblyopic subjects.

Clinical Observations in Cyclodeviations

Cyclodeviations differ from other strabismus forms in several aspects. Adaptive mechanisms other than suppression cause the patient to remain asymptomatic in spite of ophthalmoscopically demonstrable torsion of the globe around the sagittal axis. These mechanisms include cyclofusion and a monocular sensory adaptation causing the images seen by the paretic eye to appear vertically and horizontally aligned even though they do not fall on the vertical and horizontal anatomic-geometric retinal meridians. Pure excyclotropias, ie, those not associated with vertical deviations, respond well to anterior and lateral displacement of the anterior portion of the superior oblique tendon. The operation elminated the cyclodeviation in four eyes (three patients); however, a partial recurrence was observed in one case.

High myopia as an unusual cause of restrictive motility disturbance

Endocrine ophthalmopathy is a common cause of restrictive ocular motility disorder associated with abnormal forced duction testing. We report ultrasonographic and computed tomographic findings in a highly myopic patient without thyroid abnormality in whom the restrictive findings of endocrine ophthalmopathy were simulated by contact between elongated globes and the bones of the orbital apices.

Effect of Isolated Inferior Oblique Muscle Myectomy in the Management of Superior Oblique Muscle Palsy

Thirty-three patients with superior oblique palsy were treated with an inferior oblique myectomy temporal to the inferior rectus muscle. The mean effect of surgery was 11.91 +/- 1.38 in all positions of gaze and for all age groups. The operative result in both children and adults was the same. The mean effect of surgery correlated with the size of the preoperative hyperdeviation in the fields of action of both inferior and superior oblique muscles. Inferior oblique muscle myectomy was followed by return of normal function to the superior oblique muscle in 63% of cases. Ocular torticollis was eliminated in 90% of the patients. Persistent overaction of inferior oblique muscle was encountered in three patients. Postoperative underaction of the myectomized muscle was not observed in any of our patients. A myectomy is recommended as a primary procedure in patients with superior oblique muscle palsy when the direct antagonist is overacting and the hyperdeviation is 10 to 15 prism diopters or more in primary position or the fields of action of the paretic superior oblique muscle or the overacting inferior oblique muscle.

Adaptation to Tilting of the Visual Environment in Cyclotropia

We evaluated adaptations to tilting of the visual environment in 18 patients with cyclotropia by comparison of subjective tests for torsion with the actual rotation of the globes determined by fundus photography. Patients with congenital cyclotropia had a sensory reorientation of the spatial values of retinal meridians in the cyclotropic eye that prevented awareness of tilting of the environment under uniocular and binocular conditions. Patients with cyclotropia acquired as adults in many instances also had retinal sensory reorientations of the cyclotropic eye or eyes. Additionally, they used spatial clues from the visual environment to correct for image tilting under uniocular conditions. Under dissociated binocular conditions, however, these patients became aware of tilting of the visual environment, and therefore these adaptations were less deeply rooted than those in patients with congenital cyclotropia. Because certain patients with acquired cyclotropia showed evidence of using these adaptations under uniocular conditions but had constant or intermittent torsional diplopia under casual binocular viewing conditions, binocular mechanisms such as cyclofusion, suppression, and anomalous retinal correspondence may also be necessary to eliminate subjective tilting of the visual environment.

Accommodative convergence in hypermetropia

We compared the clinical characteristics of esotropic, hypermetropic children whose strabismus was fully corrected with spectacles (refractive accommodative esotropia) with those who remained orthotropic (that is, had no manifest strabismus on the cover test) in the presence of uncorrected hypermetropia. In addition to a standard ophthalmologic and orthoptic examination, we determined the stimulus accommodative convergence/accommodation (AC/A) ratio by using the gradient method over a range of 6 diopters, the near point of accommodation, and random dot stereopsis. Hypermetropic patients without esotropia or significant esophoria were found to have a low AC/A ratio in contrast to those patients with refractive accommodative esotropia. This finding explains why esodeviations may be absent in some hypermetropic patients with uncorrected vision. We found a high prevalence of abnormally low near points of accommodation and defective or absent stereopsis in both groups of patients.