G K von Noorden

Behavioral studies on the effect of abnormal early visual experience in monkeys: Spatial modulation sensitivity

Spatial modulation sensitivity functions have been investigated by behavioral methods in two monkeys reared with normal visual experience and 12 monkeys reared with abnormal, early visual experience. Experimental treatments were initiated when the animals were approximately one month of age. Two monkeys were each treated with one of the following procedures: (1) long-term monocular lid suture, (2) short-term monocular lid suture, (3) surgically induced esotropia, (4) surgically induced exotropia, (5) optical dissociation of binocular vision with ophthalmic prisms, or (6) chronic monocular cycloplegia. The results of the studies showed a severe loss of contrast sensitivity of the treated eyes compared to the control eyes for monkeys reared with monocular lid suture or surgically induced esotropia. Surgically induced exotropia resulted in a moderate reduction in sensitivity of the deviated eye while optical dissociation resulted in a mild reduction in sensitivity of one eye compared to the other. One of the two monkeys reared for seven months with chronic monocular cycloplegia had a relative reduction in contrast sensitivity of the treated eye, but the other monkey had equal sensitivities in the two eyes. However, binocular summation experiments showed that even though the relative difference between the monocular sensitivities was small or absent for the monkeys reared with optical dissociation or chronic monocular cycloplegia, none of them demonstrated binocular vision in these experiments.

Current concepts of infantile esotropia

Several forms of esotropia with a different pathophysiology that meet the criterion of an onset early in life must be distinguished from essential infantile esotropia. A hypothesis is presented, according to which a delayed development or a congenital defect of retinal disparity sensitivity (motor fusion) in an otherwise normal infant with immature sensory functions causes esotropia under the influence of various strabismogenic factors. Some of these factors are genetically determined, hence the familial occurrence of essential infantile esotropia. The absence or marked decrease of stereopsis and the asymmetry of optokinetic nystagmus are interpreted as the consequence of ocular misalignment early in life rather than of structural anomalies in the afferent visual pathways of esotropic patients. The therapeutic results after surgery are classified into four groups: subnormal binocular vision, microtropia, small angle eso- or exotropia and large angle residual or consecutive eso- or exodeviations. Analysis of data from 358 operated patients with a documented onset of esotropia prior to the sixth month of life has shown that the probability of obtaining an optimal functional result is increased when surgical alignment is completed before completion of the second year of life. However, surgery after the age of two or even four years of life does not preclude the development of binocular vision on a subnormal or anomalous basis.Several forms of esotropia with a different pathophysiology that meet the criterion of an onset early in life must be distinguished from essential infantile esotropia. A hypothesis is presented, according to which a delayed development or a congenital defect of retinal disparity sensitivity (motor fusion) in an otherwise normal infant with immature sensory functions causes esotropia under the influence of various strabismogenic factors. Some of these factors are genetically determined, hence the familial occurrence of essential infantile esotropia. The absence or marked decrease of stereopsis and the asymmetry of optokinetic nystagmus are interpreted as the consequence of ocular misalignment early in life rather than of structural anomalies in the afferent visual pathways of esotropic patients. The therapeutic results after surgery are classified into four groups: subnormal binocular vision, microtropia, small angle eso- or exotropia and large angle residual or consecutive eso- or exodeviations. Analysis of data from 358 operated patients with a documented onset of esotropia prior to the sixth month of life has shown that the probability of obtaining an optimal functional result is increased when surgical alignment is completed before completion of the second year of life. However, surgery after the age of two or even four years of life does not preclude the development of binocular vision on a subnormal or anomalous basis.

Recession of Both Horizontal Recti Muscles in Duane's Retraction Syndrome With Elevation and Depression of the Adducted Eye

Upshoot and downshoot of the adducted eye in Duanes retraction syndrome is thought to be caused by a bridle effect of the co-contracting horizontal recti muscles. A recession of both of these muscles transposes their insertions posteriorly in relation to the center of rotation of the globe, which reduces the bridle effect and decreases the upshoot and downshoot. An 11-year-old girl had Duanes retraction syndrome type III and upshoot and downshoot of the left eye. The left lateral rectus muscle was recessed 8 mm and the left medial rectus muscle 6 mm. At last examination 10 1/2 months postoperatively, the upshoot and downshoot on attempted adduction was no longer present.

Loss of stereopsis in monkeys following prismatic binocular dissociation during infancy

Prismatic binocular dissociation was used during infancy to mimic conditions of strabismus in macaque infants. Prisms worn continuously produce a diplopia unfavorable for the maintenance and development of the binocular visual system. Prism-reared monkeys were tested as young adults and found to be permanently stereoblind for dynamic random dot stereograms. Control monkeys did comparably to humans on such tests. It is concluded that short periods of diplopia attendant with strabismus are sufficient to produce permanent stereoblindness.

The effects of reverse monocular deprivation in monkeys II. Electrophysiological and anatomical studies

SummaryMonkeys had one eye closed at about 30 days of age for 14, 30, 60, or 90 days, then opened, and the fellow eye closed for another 120 days. The animals then had at least 10 months of binocular visual experience before extensive behavioral training and testing were carried out. In terminal experiments concluded more than 18 months later, microelectrode investigations of the striate cortex demonstrated that there was almost a complete absence of binocular neurons in all animals. The initially deprived eyes (IDEs) dominated the majority of cortical neurons, even when soma size measurements of lateral geniculate neurons indicated that the LGN cells driven by the IDE had not regained their normal size. The monkeys which had significant interocular differences in spatial vision also exhibited abnormalities in the distribution of the metabolic enzyme, cytochrome oxidase (CO), within the striate cortex. These results demonstrate that many of the severe alterations in cortical physiology and eye dominance produced by early monocular form deprivation can be reversed, with recovery of normal cortical function, via the reverse-deprivation procedure.

Childhood acute leukemia: A search for occult extramedullary disease prior to discontinuation of chemotherapy

Between January 1978 and September 1979, 29 children with acute leukemia in complete continuous remission for three or more years were examined for evidence of occult extramedullary disease immediately prior to discontinuation of chemotherapy. Bilateral open wedge testicular biopsy demonstrated the presence of bilateral leukemic infiltrates in 2/13 boys. Gallium scans prior to biopsy had identified unilateral infiltration in an enlarged testis in one patient but failed to identify microscopic disease in the opposite testis or in the testes of the second patient. Percutaneous kidney and liver biopsies, pelvic ultrasonography, intravenous pyelogram, skeletal survey, cranial computed axial tomography scan, electroencephalography, and ophthalmologic examinations failed to demonstrate evidence of occult disease. Except for testicular biopsy, this study does not support extensive clinical or invasive procedures to identify extramedullary disease prior to discontinuation of chemotherapy.

The Bagolini striated lens test for cyclotropia

Measurements of cyclotropia obtained by two different techniques were compared in ten patients with superior oblique palsies. These techniques were the Maddox double rod test and a new test for cyclotropia using the Bagolini striated lenses. In contrast to the Maddox rods, the Bagolini lenses permit a nearly normal view of the visual environment; in addition with the Bagolini striated lens test, the patients eyes were not prismatically dissociated as in the Maddox double rod test, but instead prisms were used when necessary to eliminate horizontal and vertical image disparities prior to measuring cyclotropia. The Bagolini striated lens test thereby permitted cyclotropia adaptive mechanisms to function under nearly normal viewing conditions. The two tests yielded similar measurements of cyclotropia under dissociated binocular conditions, but in several patients different results were found with the Bagolini striated lenses when associated vertical and horizontal heterotropias were eliminated spontaneously or prismatically. Three cases are reported in whom the Bagolini striated lens test provided important clinical information not revealed by the Maddox double rod test.

Keeping an eye on the brain: the role of visual experience in monkeys and children

The quality of visual experience during infancy determines the functional sensitivity and precision of the mature primate visual system. Infant monkeys subjected to monocular form deprivation show a period of critical visual development that, though decreasing in sensitivity, lasts throughout the first 2 years of life. Photopic threshold spectral sensitivity appears to have a briefer critical period, which is essentially complete by 6 months old, whereas scotopic visual functions appear well developed by 3 months old. Binocular visual functions seem to have the longest period of sensitivity to abnormal visual experience because periods of monocular form deprivation initiated during the first 2 years affect visual functions. Viewing the world through prisms, which mimics the condition of strabismus, causes a permanent loss of cortical binocular cells and stereopsis in monkeys. This result explains stereoblindness in children having equivalent clinical histories.

Excitatory binocular neurons are lost following prismatic binocular dissociation in infant monkeys.

Four infant rhesus monkeys had prismatic dissociation of binocular vision by viewing the world through prisms. Those monkeys tested previously for ability to utilize horizontal disparity cues in detection of dynamic random dot stereograms, were found here to have few excitatory binocular neurons in visual cortex (V1). Each eye was well represented in the monocular ability to drive cortical neurons, whilst stimulus orientation tuning appeared normal in the monocular neurons, but somewhat less sensitive in the remaining binocular neurons. Binocular dissociation early in life constitutes conditions unfavorable for the maintenance of neural connections delivering binocular excitation to the visual cortex.

Shrinkage and recovery of cells of the lateral geniculate nuclei with prism-rearing in macaques

Infant macaque monkeys (Macaca mulatta) were subjected to optical dissociation of binocular vision by wearing prisms before their eyes for 30 days, beginning about 30 days of age. Such treatment mimicked strabismus during infancy and resulted in a dramatic loss of cortical binocular neurons. A concurrent shrinkage of 21% was found in the cells of the lateral geniculate nuclei (LGN) at the end of a terminal electrophysiological study at 60 days of age. A group of monkeys surviving for 5 years showed recovery of normal cell size, even though they did not recover functional binocular neurons in visual cortex.