Constant Strabismus Research Articles

Maximum angle of horizontal strabismus consistent with true stereopsis

BackgroundWe prospectively evaluated the performance of three stereoacuity tests in patients with a wide range of strabismus angles to determine the maximum angle of horizontal strabismus consistent with true stereopsis as well as the extent of false-positive results. MethodsSubjects age ≥ 5 years old (n = 186) with constant horizontal strabismus were prospectively studied. Stereoacuity was measured using the Titmus Fly, Animals, and Circles tests; the original Preschool Randot test; and the Frisby test. We defined a false-positive result as any positive response to a stereoacuity test when a patient had > 20 prism diopters (PD) of deviation. Based on the results from our previous study of monocularly patched adults, we then defined a true-positive result as Titmus circles five to nine, at least 400“ on the original Preschool Randot test, or a pass on the Frisby test. Data were then analyzed to determine a maximum deviation consistent with true stereopsis. ResultsFalse-positive results occurred with Titmus Fly (6%), Titmus Animals (10%), Titmus Circles (35%), and the 800 seconds of arc (”) level of the original Preschool Randot test (10%). No false-positive results were seen with the Frisby test. Applying the criteria for a true-positive result, we found that no patient with > 10 PD of deviation had true stereopsis. The two patients with 10 PD and 6 PD deviations could not subsequently pass the Frisby test and were therefore deemed not to have true stereopsis. We concluded that the threshold for true stereopsis may be as low as 4 PD of horizontal deviation. ConclusionIn summary, the Titmus Fly, Titmus Animals, and Titmus Circles (the first four circles) tests possess monocular clues that limit their usefulness for clinical testing. The Frisby test is particularly useful for rapid assessment of whether stereopsis is present or absent. The new Preschool Randot test is valuable for quantifying stereopsis in both children and adults. True stereopsis may be rare when a patient has a horizontal deviation > 4 PD.

Pediatric Vision Screener 2: pilot study in adults

Amblyopia is a form of visual impairment caused by ocular misalignment (strabismus) or defocus in an otherwise healthy eye. If detected early, the condition can be fully treated, yet over half of all children with amblyopia under age 5 escape detection. We developed a Pediatric Vision Screener (PVS) to detect amblyopia risk factors. This instrument produces a binocularity score to indicate alignment and a focus score to indicate focus. The purpose of this study is to assess the performance of the PVS by testing adults who were fully cooperative for testing. The study group includes 40 subjects (20 controls, 20 patients) aged 22 to 79 years. 12 patients had constant strabismus (8 to 50Delta), and eight had variable strabismus (12 to 55Delta). All controls had binocularity scores >50%. Binocularity was <50% in 11/12 patients. The patient with binocularity >50% had a well-controlled intermittent exotropia and was not at risk for amblyopia. Focus scores were highly sensitive for good focus but not specific. The PVS shows high sensitivity and specificity for detection of strabismus in adults. Future studies will determine whether this performance can be achieved in preschool children, who are at greatest risk for vision loss.

The polaroid suppression test in a pediatric population with ophthalmologic disorders.

The Polaroid suppression test (PST) is a new method for early detection of amblyogenic factors by screening for suppression. The apparatus can elicit suppression with the use of Polaroid filters. The aim of the present study was to examine a population of children with known ophthalmologic disorders using the PST to determine the rate of false-negative results of the PST. Six hundred four children, varying in age between 3 and 15 years (mean, 7.9) were examined using the PST. Ophthalmologic disorders ranged from strabismus and amblyopia to refractive disorders. Mean testing time for the PST was 43 seconds. The PST could not be administered to 34 children (5.6%); 443 children (73.3%) had abnormal results; and 127 children (22.2%) showed no suppression. The suppression in constant strabismus was detected in almost all cases. The sensitivity for accommodative forms of strabismus was lower, but amblyopia was never missed in these cases. In children with normal eye alignment, only 2.7% with an interocular acuity difference of more than 0.1 logMAR had no suppression. Of all 119 children with clinical defined amblyopia, only 1 (0.8%) did not have suppression. Overall sensitivity of the PST for strabismus and/or abnormal interocular acuity difference was 96.2% and specificity was 41.1%. The PST has great potential as a visual screening tool in young children. Only few children with amblyogenic factors were missed. Thus, the test can differentiate those children at risk for amblyopia from normally sighted children. Because specificity is lower, all children showing suppression with the PST in a screening situation should have further examination by the health care worker before being referred to the ophthalmologist.

The polaroid suppression test in a pediatric population with ophthalmologic disorders

Purpose The Polaroid suppression test (PST) is a new method for early detection of amblyogenic factors by screening for suppression. The apparatus can elicit suppression with the use of Polaroid filters. The aim of the present study was to examine a population of children with known ophthalmologic disorders using the PST to determine the rate of false-negative results of the PST. Methods Six hundred four children, varying in age between 3 and 15 years (mean, 7.9) were examined using the PST. Ophthalmologic disorders ranged from strabismus and amblyopia to refractive disorders. Results Mean testing time for the PST was 43 seconds. The PST could not be administered to 34 children (5.6%); 443 children (73.3%) had abnormal results; and 127 children (22.2%) showed no suppression. The suppression in constant strabismus was detected in almost all cases. The sensitivity for accommodative forms of strabismus was lower, but amblyopia was never missed in these cases. In children with normal eye alignment, only 2.7% with an interocular acuity difference of more than 0.1 logMAR had no suppression. Of all 119 children with clinical defined amblyopia, only 1 (0.8%) did not have suppression. Overall sensitivity of the PST for strabismus and/or abnormal interocular acuity difference was 96.2% and specificity was 41.1%. Conclusions The PST has great potential as a visual screening tool in young children. Only few children with amblyogenic factors were missed. Thus, the test can differentiate those children at risk for amblyopia from normally sighted children. Because specificity is lower, all children showing suppression with the PST in a screening situation should have further examination by the health care worker before being referred to the ophthalmologist.

Intractable diplopia after strabismus surgery in adults.

To investigate the incidence of persistent intractable diplopia in adults undergoing surgery for long-standing, constant strabismus and to define tests that may be useful for identifying patients at risk for developing this complication. A retrospective medical record review of adults without diplopia undergoing surgery for constant strabismus. Medical records of 424 adult patients undergoing strabismus surgery were studied. Of these patients, 143 (34%) experienced diplopia when tested preoperatively with prisms to simulate the desired surgical outcome. Only 40 patients (9%) had temporary diplopia after surgery, which resolved in all cases by 6 weeks postoperatively. Three patients (0.8%) developed persistent intractable diplopia. Experiencing diplopia with preoperative prism testing was significantly more likely to result in postoperative diplopia than if diplopia was not present preoperatively (P<.001 and P =.04 for temporary and persistent postoperative diplopia, respectively). Preoperative testing had a sensitivity and negative predictive value for temporary postoperative diplopia of 100%, a specificity of 73%, and a positive predictive value of 28%. Similar values were found for persistent diplopia after surgery with the exception of the positive predictive value, which was only 2%. Patients who did not see double during preoperative testing with prisms never developed diplopia after surgery. However, the presence of preoperative diplopia with prism testing (including a prolonged trial with Fresnel prisms) was infrequently predictive of postoperative diplopia. Intractable diplopia after strabismus surgery in adults without previous diplopia is very rare. The diagnostic use of prisms prior to surgery may identify some patients who have little or no risk of postoperative diplopia, as well as a group of patients with a small but definite risk of intractable postoperative diplopia.

Prevalence of systemic and ocular disease in infantile exotropia: Comparison with infantile esotropia

Objective Exotropia in infancy is believed to be associated with an increased prevalence of neurologic, ocular, and craniofacial abnormalities; however, the prevalence of coexisting ocular and systemic disease in these patients is unknown. In this study, the prevalence of ocular disease and systemic illness was determined in patients diagnosed with exotropia in infancy. Design Observational comparative case series. Participants Medical records of 70 patients diagnosed with exotropia in the first year of life were reviewed and compared with records of 136 patients diagnosed with esotropia before 1 year of age. Intervention Patients with no disorders (other than latent nystagmus, dissociated vertical deviation, or oblique muscle overaction) were grouped as “simple” strabismus. Patients with systemic disorders (including prematurity, neurologic disease, and genetic disease) and patients with ocular disorders (including congenital nystagmus, other strabismus, ptosis, and any condition associated with loss of vision [except amblyopia]) were grouped as “complex” strabismus. Main outcome measures Prevalence of coexisting systemic and ocular disorders. The demographics, strabismus measurements, and types of coexisting disease in the simple and complex groups were compared. Results A high percentage of both exotropia (67%) and esotropia (49%) patients had a coexisting ocular or systemic abnormality. Exotropia patients with a constant strabismus were more likely to have coexisting ocular or systemic disease than those with an intermittent strabismus. Smaller angles of exotropia or esotropia were associated with a higher likelihood of coexisting ocular or systemic diseases. Systemic disorders were found more frequently than ocular disorders in both the exotropia and esotropia groups. In 25% of all patients referred for evaluation of strabismus, an additional ocular or systemic abnormality was discovered by the ophthalmologist. Conclusion Patients presenting to a university hospital-based practice in the first year of life with exotropia were more likely than those presenting with esotropia to have coexisting ocular and systemic disease. Both groups had a notably high prevalence of associated disorders. The percentages measured in this population may not be applicable to other practices because of referral bias. However, clinicians should consider that children presenting with infantile exotropia and esotropia appear to be at risk for coexisting ocular or systemic disease.

Spatial scale shifts in amblyopia

We used a masking paradigm to uncover the properties of the mechanisms engaged by the amblyopic visual system for vernier acuity and b'ne detection. Line vernier and line detection thresholds were measured in the presence of one-dimensional noise masks varying in orientation, spatial frequency content or contrast. Our results reveal that in both normal and amblyopic eyes, there is a bimodal orientation tuning function for vernier acuity i.e. vernier acuity is most strongly masked by mask orientations approx. ± 10 deg on either side of the target lines. In contrast, in both normal and amblyopic eyes, line detection is most strongly masked when the mask and b'ne target have the same orientation. In the normal fovea, the spatial frequency tuning is bandpass, with a peak spatial frequency of about 10 c/deg. In the amblyopic eyes, the spatial tuning is similar in specificity; however the peak is shifted to lower spatial frequencies, suggesting a shift in the scale of spatial processing of line stimuli. For all of the amblyopic eyes, the increased line detection thresholds are approximately proportional to the shift in spatial scale. In anisometropic amblyopes, the (unmasked) vernier threshold is elevated in proportion to the shift in spatial scale; however in some amblyopes with constant strabismus the shift in spatial scale is not sufficient to account for the degraded vernier acuity. The “extra” increase in vernier thresholds associated with strabismus may be a consequence of a high degree of positional uncertainty which adds noise at a stage following the combination of filter responses.

Polaroid Photoscreening for Amblyogenic Factors: An Improved Methodology

The authors describe a new photoscreening camera designed to detect amblyogenic factors, including strabismus, asymmetric and abnormal refractive errors, and media opacities. The photoscreener uses eccentric photorefraction principles and provides two meridian photographs of the retinal reflex. Pass/fail screening data from the photographs of 202 nondilated children as determined by two masked observers were compared with data from complete ophthalmologic examinations. The photoscreener had a sensitivity rate of 87%, a specificity rate of 89%, a positive predictive value of 93%, a negative predictive value of 80%, and an overall agreement rate of 88%. The prescreening probability for amblyogenic factors was 63%. Constant strabismus was detected in all cases. Five intermittent strabismus cases were missed. Two patients with myopia, three patients with hyperopia, and five patients with astigmatism were missed. All media opacities were detected. This new two-flash photoscreening camera, which uses high-speed Polaroid film, is an accurate, reliable method of detecting amblyogenic factors in undilated children. The camera offers promise as a useful mass screening tool.

Postoperative Binocularity in Adults with Longstanding Strabismus

The authors tested preoperatively and postoperatively for binocularity with the Bagolini lenses in a series of 359 adults who underwent surgery for long-standing constant strabismus. Eighty-six percent of patients showed a binocular response with the Bagolini lens test almost immediately after surgery. Regardless of the type of deviation present preoperatively, the duration of strabismus, or the depth of amblyopia in the deviating eye (if present), the vast majority of patients developed binocularity. The development of binocularity with the Bagolini lenses after surgery appears to be related to the stability of the postoperative ocular alignment.

Postoperative Binocularity in Adults with Long Standing Strabismus: Is Surgery Cosmetic Only?

In a series of 324 adults who underwent surgery for long standing constant strabismus, 85% developed binocularity as determined with the Bagolini lens almost immediately postoperatively. The vast majority of patients developed binocularity regardless of the type of deviation present preoperatively, duration of the strabismus, or depth of amblyopia (if present) in the deviating eye. The vast majority of adults with constant long standing strabismus will develop a functional improvement if their eyes are satisfactorily aligned.

Acquired monofixation syndrome.

Monofixation syndrome is a well documented sensory abnormality occurring in patients with childhood-onset strabismus. We report the development of monofixation syndrome in six adults with strabismus. It is proposed that constant strabismus, which precludes and prevents bifixation, can result in the development of monofixation syndrome if the strabismic deviation is not corrected promptly.

An unexpected role for normal accommodative vergence in strabismus and amblyopia.

Accommodative vergence was measured using the Müller experimental paradigm in which target movement along the line of sight of the viewing eye results in large movement of the fellow (covered) eye. Our paper demonstrates an unexpected predominance of accommodative vergence over disparity vergence in patients with constant strabismus amblyopia, intermittent strabismus, and amblyopia without strabismus. Comparison of accommodative vergence responses in these patients with responses from normal subjects using symmetrical and asymmetrical targets under binocular and monocular conditions established the normal character of the patients' accommodative vergence and the absence of disparity vergence in most of them. The intermittent absence of disparity vergence in certain of our patients--some with surgically corrected strabismus, some with moderate amblyopia, and some with amblyopia treated with orthoptics--raises questions of clinical and neurophysiological interest. Preliminary results on the effects of amblyopia on accommodative responses are also presented.

Increased drift in amblyopic eyes.

Reports are conflicting on the presence of increased drift in amblyopic eyes. Furthermore, the individual effects of either amblyopia or strabismus alone on ocular drift have not been systematically investigated. We therefore used a photoelectric method to record horizontal eye position during monocular and binocular fixation in patients having amblyopia without strabismus, intermittent strabismus, or constant strabismus amblyopia. Our principal finding was increased drift amplitude (up to 3.5 degree) and velocity (up to 3.0 degrees per second) in amblyopic eyes during monocular fixation. While increased drift was found 75% of the time in amblyopia without strabismus and 50% of the time in constant strabismus amblyopia, it was found only 20% of the time in intermittent strabismus. Amblyopic drift could be either error-producing or error-correcting in nature. Increased drift was not present during monocular fixation with the dominant eye or during binocular fixation in any of our 16 patients. We therefore conclude that amblyopia and not strabismus is a necessary condition for the presence of markedly increased fixational drift. Increased drift amplitude but not velocity may adversely affect visual acuity in the amblyopic eye.

Saccadic intrusions in strabismus.

Fixational eye movements were studied to determine the presence of and to quantify saccadic intrusions under monocular and binocular viewing conditions in subjects with intermittent strabismus, amblyopia without stabismus, or constant strabismus amblyopia. Saccadic intrusions were present under most test conditions in intermittent strabismus, were rarely observed in amblyopia without strabismus, and were prominent during monocular fixation with the amblyopic eye in constant strabismus anblyopia. This suggests that the presence of saccadic intrusions was related to strabismus and not amblyopia. There was no relationship between saccadic intrusion amplitude and visual acuity. Two possible mechanisms for producing intrusions are abnormally rapid regional visual adaptation and strabismus-induced fixation degradation.

Suppression of Fixational Saccades in Strabismic and Anisometropic Amblyopia

Individuals with strabismus frequently exhibit large fixational saccadic pairs (saccadic intrusions) during monocular fixation with the amblyopic eye in the light. We found two conditions in which the saccadic intrusion frequency could be markedly reduced. When instructed to ‘hold the eye steady’ in the presence of a visible target in the light, saccadic intrusions were suppressed and eye position maintained within a few degrees of the target. These results suggest that corrective drift was used by the amblyopic eye to aid in position maintenance. When instructed to ‘fixate’ in complete darkness, the intrusive pattern was replaced by a jerk nystagmus-like pattern. These results clearly demonstrate that saccadic intrusions in amblyopic eyes require the presence of a visible target for their generation, and additionally, that ‘extraretinal signals’ were involved in maintenance of eye position under this condition. Saccades could also be suppressed during the ‘hold’ command in the light by patients having amblyopia without strabismus or constant strabismus amblyopia with intermittent jerk nystagmus.

Processing delays in amblyopic eyes: evidence from saccadic latencies.

Saccadic latencies were measured in amblyopes with constant strabismus, amblyopes without strabismus, and intermittent strabismics with or without amblyopia. Subjects tracked a small spot of light, either monocularly or binocularly, which moved with random horizontal step displacements of 0.25--8.5 deg over the central field. Increased saccadic latencies were observed in the amblyopic eyes of 6 of 11 subjects, with or without strabismus; saccadic latencies were similar in each eye of 2 subjects having intermittent strabismus without amblyopia. Amblyopia was a necessary condition for increased saccadic latencies and not strabismus. Evidence for normal motor control of eye movements in amblyopic subjects is as follows: normal saccadic durations in the amblyopic eyes, normal saccadic-latency distribution curves for binocular tracking and monocular tracking with the nonamblyopic eyes, and synchronous movements of the 2 eyes. Our results are interpreted in terms of a processing delay in the sensory pathways leading from the central region of the amblyopic eye to the centers involved in saccadic initiation.

The Setting‐sun Eye Phenomenon in Infancy

In a longitudinal study, 19 infants who displayed the setting-sun eye phenomenon were observed during the first year of life. Nine of the infants showed no signs of illness, eight had an evident increase in intracranial pressure requiring surgical relief, and two had transient signs of increased intracranial pressure which resolved spontaneously. The setting-sun phenomenon could be elicited both by alteration of the infant's position and by removal of light, and it also occurred spontaneously. The effectiveness of the eliciting mechanism depended on the age of the infant. The component parts of the phenomenon consist of downward rotation of the eyeballs and retraction of the upper eyelids, sometimes accompanied by raising of the brow. The phenomenon can be observed in healthy infants, and its value in early recongnition of increased intracranial pressure is limited. The response might indicate increased intracranial pressure if it can be elicited by alteration of position in infants older than four weeks of age or if there is a marked response to removal of light in infants younger than eight weeks or older than 20 weeks of age, especially if the response is combined with constant or intermittent strabismus or undulating eye-movements.

Strabismus in Children Corrected by Refraction Alone

The results of correcting the refractive errors in 185 cases of constant concomitant strabismus are presented. Squint had existed at least one year previous to the wearing of glasses. No atropinization nor occlusion nor orthoptic training was attempted. A high degree of squint, amblyopia, severe defects in motility and in fusion were the greatest obstacles to recovery. The patients under four years of age recovered more quickly than those over four. The accommodative type of squint recovered more readily than any other type. Of the 185 cases, 63.4 percent were unimproved, 13 percent were improved, and 23.6 had no squint with glasses. From the Department of Ophthalmology, Children's Memorial Hospital, Chicago, Illinois. Presented before the Chicago Opthalmological Society, February 18, 1935.