Knapp's law and unilateral axial high myopia. 1970.

BACKGROUND AND PURPOSE: (Hermann) Knapp's Law states, in essence, that in axial ametropia, if the correcting lens is placed so that its second equivalent point coincides with the anterior focus of the eye (ca 15 mm in front of the eye), the size of the retinal image is not different from that in the normal eye. The advent of ocular ultrasonic echography and axial biometry permits us to now test this Law. METHODS AND SUBJECTS: A "Direct Comparison" Eikonometer was devised using the Aulhorn Phase- Difference Haploscope, projectors, and half circle targets with equalized luminance. Five patients with anisomyopia were tested for aniseikonia after complete ophthalmologic examination including also A-Scan ultrasonic echography axial biometry. RESULTS: Significant aniseikonia was found in all five subjects ranging from 10% to 60% angular minification in the myopic eye. Ultrasonic axial biometry showed axial length differences from 2 to 5 1/2 mm with reasonable correlations between axial length differences and both clinical ametropia (anisomyopia) and the amount of aniseikonia found. CONCLUSIONS: Knapp's Law may be optically right but clinically wrong. That is, its clinical application, which predicts the absence of aniseikonia in axial aniosometropias is not fulfilled. Retinal stretching due to myopia and resultant retinal micropsia is hypothesized to be the cause of this optically unexpected aniseikonia. The retinal images may be isometric but the patient will still have significant cortically perceived or perceptual aniseikonia due to retinal microspia. Such patients may benefit from contact lenses or other aniseikonic corrections.

Stereopsis and disparity vergence in monkeys with subnormal binocular vision.

The surgical treatment for strabismus in infants generally results in microtropia or subnormal binocular vision. Although the clinical characteristics of these conditions are well established, there are important questions about the mechanisms of binocular vision in these patients that can best be investigated in an appropriate animal model. In the present psychophysical investigations, spatial frequency response functions for disparity-induced fusional vergence and for local stereopsis were studied in macaque monkeys, who demonstrated many of the major visual characteristics of patients whose eyes were surgically aligned during infancy. In six rhesus monkeys, unilateral esotropia was surgically induced at various ages (30-184 days of age). However, over the next 12 months, all of the monkeys recovered normal eye alignment. Behavioral measurements at 4-6 years of age showed that the monkeys' prism-induced fusional vergence responses were indistinguishable from those of control monkeys or humans with normal binocular vision. Investigations of stereo-depth discrimination demonstrated that each of the experimental monkeys also had stereoscopic vision, but their stereoacuities varied from being essentially normal to severely stereo-deficient. The degree of stereo-deficiency was not related to the age at which surgical esotropia was induced, or to the presence or absence of amblyopia, and was not dependent on the spatial frequency of the test stimulus. Altogether, these experiments demonstrate that a temporary, early esotropia can affect the binocular disparity responses of motor and sensory components of binocular vision differently, probably because of different sensitive periods of development for the two components.

Horizontal transposition of the vertical rectus muscles for cyclotropia.

PURPOSE: We studied the effect of horizontal transposition of the vertical rectus muscles on incyclotropia and excyclotropia in terms of the amount of correction obtained and the stability of the outcome. METHOD: Preoperative measurements for cyclotropia were compared in 11 patients with measurements during the immediate postoperative period and last follow-up. Excyclotropia was treated with nasal transposition of the inferior rectus muscle and incyclotropia with nasal transposition of the superior rectus muscle, to which we added temporal transposition to the inferior rectus muscle in one patient to enhance the effect. RESULTS: Fusion in all gaze positions was restored in six patients and functional improvement occurred in five. The average effect of horizontal transposition of one vertical rectus muscle for cyclotropia was a correction of 7 degrees in primary position and of 11 degrees in depression. This effect remained stable after a mean follow-up of 17 months, and additional improvement occurred in one patient. One patient developed a hypertropia, eliminated by an additional operation, in the treated eye. CONCLUSIONS: For excyclotropia, nasal transposition of the inferior rectus muscle is a viable alternative to lateral and anterior transposition of the anterior portion of the superior oblique tendon. It becomes the procedure of choice when surgery on the superior oblique tendon is precluded, either by the tendon's congenital absence or by previous surgery on the tendon. Nasal transposition of the superior rectus muscle or temporal transposition of the inferior rectus muscle is ideally suited for incyclotropia. No comparably effective operation exists.

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.

Judgments by monkeys of apparent depth in dynamic random-dot stereograms.

Young macaques discriminated apparent depths of targets embedded in dynamic random dot stereograms; a test of stereopsis. In a 'same/different' paradigm, the discrimination took longer if the pair of stimuli appeared to be in same depth plane, than when they appeared to be located in a different depth plane. The decision time was an inverse function of the disparity difference. Apparent depth discrimination performance decreased as a function of disparity, with no differences in judgments regarding crossed or uncrossed disparities.

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.

The prevalence of dissociated vertical deviation in patients with sensory heterotropia.

PURPOSE: We reviewed 281 consecutive patients with sensory esotropia or exotropia to determine the prevalence of dissociated vertical deviation in patients with sensory strabismus. METHODS: We reviewed the charts of all patients who received a diagnosis of sensory heterotropia or dissociated vertical deviation and who were examined at the Pediatric Ophthalmology Service at the Texas Children's Hospital between 1973 and 1992. Statistical analyses of the prevalence of dissociated vertical deviation were determined after evaluating the direction of the accompanying horizontal strabismus and examining the temporal relationship of the unilateral vision loss. RESULTS: Dissociated vertical deviation was diagnosed in 35 patients (12.5%). It occurred more frequently in sensory esotropia (22 patients, 18.3%) than exotropia (13 patients, 8.1%) (P = .009). The age at which unilateral visual loss occurred did not influence the development of dissociated vertical deviation. CONCLUSION: Dissociated vertical deviation in patients with acquired loss of vision does not support the contention that dissociated vertical deviation is a genetically predetermined anomaly of binocular vision.

Strabismus in Williams syndrome.

PURPOSE: Williams syndrome is a rare genetic disorder, consisting of mental retardation, supravalvular aortic stenosis, elfin facies, and specific ocular findings, including strabismus. We undertook this study to evaluate the characteristics of the strabismus in Williams syndrome. METHODS: We examined 32 patients with Williams syndrome to determine the prevalence and define the features of the strabismus in this patient population. RESULTS: Twenty-five of the 32 patients (78%) had strabismus, esotropia being the predominant form in 23 of the 25 patients. Of the 19 patients with Williams syndrome who had infantile esotropia, seven had dissociated vertical deviation, ten had oblique dysfunction, and six had amblyopia. CONCLUSIONS: When the patients with Williams syndrome were compared to the general population, no statistically significant difference was found in the clinical characteristics of infantile esotropia between the two groups. Because of the high prevalence of esotropia in patients with Williams syndrome (72%) compared to the general population (0.1%), we postulate a genetic link between Williams syndrome and the hereditary form of infantile esotropia.

Treatment of residual dissociated vertical deviation with inferior rectus resection.

The effectiveness of an ipsilateral 4-millimeter resection of the inferior rectus muscle was evaluated as a treatment of recurrent dissociated vertical deviation. Thirty-six patients who had an unsatisfactory outcome after 7- to 9-millimeter recession of the superior rectus muscle had an ipsilateral inferior rectus muscle resection. The dissociated vertical deviation was fully corrected in 18 patients and improved in 15 patients. Only three patients (8%) had an unsatisfactory result. Multivariate analysis of four preoperative features including the amplitude of the dissociated deviation, the age at diagnosis, the age at surgery, and the degree of amblyopia failed to define any factors that could predict surgical success.

Clinical characteristics and surgical management of congenital absence of the superior oblique tendon.

We reviewed clinical characteristics and surgical results of nine patients with surgically proved congenital absence of the superior oblique tendon. The following factors indicate absence of the tendon in the setting of superior oblique palsy: (1) an associated horizontal deviation, (2) amblyopia, (3) a large hypertropia in primary position, (4) spread of comitance, and (5) pseudo-overaction of the contralateral superior oblique muscle. The nine patients required a total of 19 operations to correct their vertical and horizontal deviations. Surgical management was based on the preoperative action of the inferior oblique muscle, the amount of hypertropia in primary position, and intraoperative forced ductions. After their operations, eight of nine patients had improvement in or abatement of their symptoms, and seven of seven with preoperative head tilts had improvement of their head position.