Microtropia

Factors affecting the total occlusion time in eyes with hyperopic anisometropic amblyopia

BACKGROUND

Amblyopia treatment by occluding the healthy eye is known to be effective during a sensitive critical period. This study aims to clarify the factors for the total occlusion time (TOT) required for the amblyopic eye to achieve a normal visual acuity (VA) level of 1.0 (0.0 logMAR equivalent). This could contribute to an efficient treatment plan for eyes with hyperopic anisometropic amblyopia.

METHODS

Subjects were 58 patients (26 boys and 32 girls; age range, 3.6-9.2, average, 5.8 ± 1.3 years) with hyperopic anisometropic amblyopia. All the subjects had initially visited and completed occlusion therapy with improved VA of 1.0 or better in the amblyopic eye at Kindai University Hospital between January 2007 and March 2017. Using the subjects' medical records, we retrospectively investigated five factors for the TOT: the age at treatment, the initial VA of the amblyopic eye, refraction of the amblyopic eye, anisometropic disparity, and the presence of microstrabismus. Patient's VA improvement at one month after treatment was also evaluated to confirm the effect of the occlusion therapy.

RESULTS

The initial VA of the amblyopic eye ranged from 0.1 to 0.9 (median, 0.4). The TOT ranged from 140 to 1795 (median, 598) hours with an average daily occlusion time of 7 hours. The initial VA of the amblyopic eye and presence of microstrabismus were the significant factors for the TOT (p < 0.01). To achieve VA of 1.0 or better, patients with an initial VA of ≤ 0.3 in the amblyopic eye required a longer TOT. Moreover, patients with concomitant microstrabismus required a 1.7-fold longer TOT compared to those without microstrabismus.

CONCLUSION

Longer daily occlusion hours and early start of the treatment will be necessary for patients with poor initial VA or microstrabismus to complete occlusion therapy within the sensitive critical period.

Prism adaptation test before strabismus surgery in patients with decompensated esophoria and decompensated microesotropia

Purpose

To evaluate the effect of Prism adaptation test (PAT) on the angle of squint in decompensated esophoria (decEPH) and decompensated microesotropia (decMET).

Methods

In this single-center retrospective study we reviewed the medical records of patients with the diagnosis of decEPH or decMET, aged at least 12 years, who were treated by strabismus surgery for the first time. The maximum Angle of squint (AOS) for far (F) and near (N) fixation and PAT results before surgery, as well as AOS (F) and AOS (N) after surgery and results of binocular function tests were considered. PAT included wearing a prism based on the largest angle for over 60 min.

Results

100 patients (mean age 37 ± 17 years) were included in the decEPH group, 82 patients (mean age 30 ± 13 years) in the decMET group. For decEPH, before surgery AOS was 25.5 ± 8.8 pdpt (F) and 23.5 ± 9.8 pdpt (N). During PAT the AOS increased significantly by 2.7 ± 4.3 to 28.2 ± 8.6 pdpt (F) and by 4.9 ± 4.5 to 28.3 ± 9.5 pdpt (N). Altogether, in 82% of decEPH patients AOS (F) and/ or AOS (N) in- or decreased by at least 3 pdpt. For decMET, before surgery AOS was 28.6 ± 10.8 pdpt for far (F) and 30.9 ± 11.8 pdpt for near fixation (N). During PAT the AOS increased significantly by 4.2 ± 5.8 to 32.5 ± 9.5 pdpt (F) and by 3.7 ± 6.1 to 34.4 ± 9.5 pdpt (N). Altogether, in 51% of decMET patients, AOS (F) and/ or AOS (N) increased by at least 10 pdpt, therefore more than 5° which would have been maximally expected from mictrotropia, or decreased by at least 3 pdpt.

Conclusions

The Prism adaptation test (PAT) showed remarkable changes in AOS in both decEPH and decMET. In patients with decEPH, the preoperative assessment of the “true AOS” under PAT reflects a pivotal requirement for successful strabismus surgery, as 82% had dose relevant angle changes ≥ 3 pdpt. For patients with decMET the preoperative prism adaptation test is especially of diagnostic value, but also 51% of decMET patients had changes in AOS beyond the expected microtropic angle (≥ 10 pdpt) or even a dose relevant angle decrease (≥ 3pdpt).

The agreement between the Irvine 4 diopter prism test and assessment of ocular fixation in microtropia with identity

Microtropia describes a primary ocular deviation of less than 10 prism diopters associated with harmonious anomalous retinal correspondence and reduced stereopsis. It is routinely accepted that children with microtropia are less likely to achieve equal vision following occlusion therapy than those with bifoveal fixation. The most commonly used methods of diagnosing a microtropia are the 4 diopter prism test (4^∆PT) and assessment of ocular fixation. This study examines the agreement between the two tests. One hundred and twelve typically developing children without a manifest strabismus who were able to undertake a linear visual acuity test and had two or more lines of anisoacuity following refractive adaption to their full cycloplegic correction underwent assessment of the 4^∆PT and ocular fixation along with their routine orthoptic examination. One hundred and twelve children (46 boys and 66 girls) attending the Orthoptic department who fitted the above criteria were included in the analysis. The mean age at examination was 6 years. 80.3% had anisometropia of at least 1.25 diopters. The 4^∆PT indicated a microtropia in 74 cases, whereas assessment of fixation indicated a microtropia in 68 cases. In 88 cases (78.6%), the results of the two tests agreed. Analysis found only moderate agreement between the two tests (k = 0.540 (CI 0.379-0.700)). Logistic regression analysis comparing those children where the two tests agreed with those where they disagreed found no difference in the level of anisoacuity (p = 0.7823), degree of anisometropia (p = 0.9385), the vision in the worst eye (p = 0.5260), the refractive error in the "worst" eye (p = 0.865), or the age at the time of testing (p = 0.4485) between the two groups. When assessing for a microtropia, it was found that not all children who elicit a central suppression response on the 4^∆PT are found to be fixing eccentrically and vice versa. This could potentially have implications for the treatment of their amblyopia. It is important not to rely on just one test at one time to make the diagnosis of microtropia. Rather, if one or other test indicates a microtropia the first time they are attempted, this should be reassessed regularly as treatment progresses and certainly before treatment is stopped and suboptimal visual acuity is accepted.

Optical Coherence Tomography in Children With Microtropia

PURPOSE

To assess whether optical coherence tomography (OCT) could be useful for detecting and documenting fixation in patients with microtropia.

METHODS

Retinal fixation observation was performed using spectral-domain OCT on amblyopic children with microtropia. The position between the retinal fixation point and the anatomical fovea was measured, in microns, using the system software tools. Only patients with a high level of cooperation, OCT scan quality signal of 7 or better, and visual acuity of 0.70 logarithm of the minimum angle of resolution (logMAR) or worse in the amblyopic eye were included.

RESULTS

A total of 25 patients were included: 15 with microtropia (study group) and 10 without tropia and with foveal fixation and stereopsis (control group). In the study group, microtropia was previously diagnosed in 67% of cases through the cover test, and was predominantly in the left eye (73%). The average visual acuity of the sound eye was 0.03 decimal and 0.18 logMAR in the amblyopic eye. The microtropia was 3.73 ± 3.34 prism diopters and eccentric fixation (387 ± 199 µm) with OCT was observed in all cases except one. Eccentricity was predominantly in the superonasal quadrant (57%). Both eyes in the control group and the contralateral eyes of the study group showed foveal fixation.

CONCLUSIONS

OCT can play an important role in the diagnosis and measurement of eccentric fixation in eyes with microtropia, providing high sensitivity. [J Pediatr Ophthalmol Strabismus. 2018;55(3):171-177.].

Laterality of amblyopia

PURPOSE

To determine the frequency of unilateral amblyopia in right versus left eyes among children younger than 18 years.

DESIGN

Analysis of data collected in randomized clinical trials conducted by the Pediatric Eye Disease Investigator Group.

METHODS

The laterality of the amblyopic eye was analyzed in 2635 subjects younger than 18 years who participated in 9 multicenter prospective, randomized treatment trials. Eligibility criteria for these clinical trials included unilateral amblyopia associated with strabismus, anisometropia, or both, with visual acuity between 20/40 and 20/400. Logistic regression was used to assess the association of baseline and demographic factors with the laterality of amblyopia.

RESULTS

Among subjects with anisometropic amblyopia (with or without strabismus), amblyopia was present more often in left than right eyes, with a relative prevalence of 59% in left eyes (95% confidence interval, 57% to 62%; P < .001 from a test of proportion, 50%). However, among subjects with strabismic-only amblyopia, there was no laterality predilection (relative prevalence of 50% in left eyes; 95% confidence interval, 47% to 54%; P = .94).

CONCLUSIONS

Anisometropic amblyopia, with or without strabismus, occurs more often in left eyes than right eyes. This finding of amblyopia laterality may be related to microtropia, sighting dominance, or other forms of ocular dominance; developmental or neurological factors; laterality in the development of refractive error; or a combination thereof.

Factors influencing severity of and recovery from anisometropic amblyopia

PURPOSE

To evaluate the correlation between the degree of anisometropia with depth of amblyopia and presence of stereopsis.

METHODS

A retrospective chart review of 119 patients treated during 1995-2004 was carried out. All patients had undergone a full ophthalmological examination. Inclusion criteria were: anisometropia >1 diopter (spherical and/or cylindrical), age at first examination between 2 and 8 years, no previous optical correction, absence of ocular and neurological disorders, absence of ocular motility disorders, and minimum follow-up of 2 years (mean 7.9 +/- 4.3). Optical correction was prescribed at first visit and, at a second visit, the need for patching or penalization was evaluated.

RESULTS

The results show a correlation between the degree of anisometropia and visual acuity at first visit (p < 0.001). There were, however, several subjects with good levels of visual acuity despite considerable anisometropia, and also subjects where mild or moderate anisometropia was sufficient to induce a severe amblyopia. Compared to other types of anisometropia, anisomyopic patients appeared to have a higher degree of binocular vision recovery when corrected optically. First evaluation with the presence of good stereoacuity seems to be a prognostic indicator for amblyopic recovery.

CONCLUSIONS

This study demonstrates the difficulty of developing a guideline for screening and treatment of anisometropia. Even though there seems to be a correlation between type and degree of anisometropia in a majority of patients, there is also a significant number of cases that do not follow this pattern. Another important observation is the presence of binocular vision at the first evaluation as a good prognostic indicator for visual recovery with optical correction alone, even without penalization therapy.

Characteristics and course of patients with deteriorated monofixation syndrome

BACKGROUND

Monofixation syndrome is characterized by small-angle strabismus with vergence fusional amplitudes and "peripheral fusion." Although it is thought to be a relatively stable condition, some patients with this syndrome deteriorate, resulting in an increasing heterotropia, sometimes associated with diplopia. Deteriorated monofixation syndrome is well known among clinicians; however, there are no studies describing the course and outcomes for these patients.

PURPOSE

To assess the clinical characteristics, course, and response to therapy of patients with deteriorated monofixation syndrome.

METHODS

We identified all patients from our database that had an ocular deviation of < or =8 Delta on simultaneous prism cover testing, peripheral fusion, and between 3000 and 67 seconds of stereoacuity (monofixators) who subsequently had an increase in their deviation to >8 Delta, loss of fusion, or diplopia. From this group we assessed patient clinical characteristics, course, and response to therapy.

RESULTS

We identified 29 patients with deteriorated monofixation syndrome who subsequently underwent treatment. Treatment consisted of surgery in 28 patients and minus lens therapy in one patient. Of the study group, 28 (97%) of the patients had a history of esotropia and 20 patients (69%) had a history of amblyopia. Nine patients noted diplopia at the time of deterioration, which persisted in four patients after treatment. In all, 14 patients (48%) met the criteria for monofixation again after therapy, while 20 patients (69%) had successful motor alignment (< or =8 Delta). There was a trend toward poorer outcomes in the diplopic group when compared with the patients who did not have diplopia, although this was not statistically significant (P = 0.26 for regaining monofixation syndrome). Follow-up ranged from 1 month to 21 years.

CONCLUSION

Though monofixation is considered a stable condition, some patients will deteriorate over time as demonstrated by an increase in the ocular deviation and loss of fusion. In this study 31% of our patients noted the onset of diplopia. Following treatment, 48% of the patients regained monofixation. Patients with diplopia following deterioration of their alignment may be less likely to regain good alignment or monofixation after treatment.

Monocular and binocular reading performance in children with microstrabismic amblyopia

AIM

To evaluate if functionally relevant deficits in reading performance exist in children with essential microstrabismic amblyopia by comparing the monocular and binocular reading performance with the reading performance of normal sighted children with full visual acuity in both eyes.

METHODS

The reading performance of 40 children (mean age 11.6 (SD 1.4) years) was evaluated monocularly and binocularly in randomised order, using standardised reading charts for the simultaneous determination of reading acuity and speed. 20 of the tested children were under treatment for unilateral microstrabismic amblyopia (visual acuity in the amblyopic eyes: logMAR 0.19 (0.15); fellow eyes -0.1 (0.07)); the others were normal sighted controls (visual acuity in the right eyes -0.04 (0.15); left eyes -0.08 (0.07)).

RESULTS

In respect of the binocular maximum reading speed (MRS), significant differences were found between the children with microstrabismic amblyopia and the normal controls (p = 0.03): whereas the controls achieved a binocular MRS of 200.4 (11) wpm (words per minute), the children with unilateral amblyopia achieved only a binocular MRS of 172.9 (43.9) wpm. No significant differences between the two groups were found in respect of the binocular logMAR visual acuity and reading acuity (p>0.05). For the monocular reading performance, significant impairment was found in the amblyopic eyes, whereas no significant differences were found between the sound fellow eyes of the amblyopic children and the control group.

CONCLUSION

In binocular MRS, significant differences could be found between children with microstrabismic amblyopia and normal controls. This result indicates the presence of a functionally relevant reading impairment, even though the binocular visual acuity and reading acuity were both comparable with the control group.

Emmetropisation in normal and strabismic children and the associated changes of anisometropia

The purpose of this study was to measure whether emmetropisation failed in children who had strabismus irrespective of their refraction in infancy, and to record simultaneous changes in anisometropia. We also report how often hypermetropia increased before these children presented with esotropia. A total of 2920 infants had a cycloplegic retinoscopy at age 5-7 months and again at 42 months or when defective vision was identified. Changes of refraction in 210 children with strabismus are compared with the remaining 2710 who did not. When the spherical equivalent of the fixing eyes was > +2.75 D in infancy, hypermetropia decreased less in both eyes of those who had microtropia (p <.001) and heterotropia (p <.001) than in normal children. When it was < +2.75 D, the spherical and/or cylindrical refraction more often remained outside the 'normal' range in both eyes of those who had microtropia and heterotropia (p <.05). Emmetropisation was deficient in both eyes of at least 80% of these strabismic children irrespective of their refraction in infancy. Furthermore, in the strabismic children, the mean change of refraction was less (p <.05) in their fellow eyes than in their fixing eyes, the difference between the two eyes being on average three times greater than that in those who had normal vision. Thus, anisometropia increased in 53% of those who had strabismus but remained within normal limits (< ca. 0.75 D spherical equivalent) in 94 % of those who did not. 'Abnormal' anisometropia in infancy did not, per se, permanently affect vision because 72% of all those who had it did not have strabismus. Finally, the spherical hypermetropia of fixing eyes increased in only 35% of the children with esotropia - similar to the incidence in those who had a microtropia (p =.36). This does not obviously support the concept that increasing hypermetropia causes accommodation to increase before convergence.

Temporal integration for stereoscopic vision

With normal binocular vision, maximal stereoacuity requires an extended viewing duration, but the relationship between the critical viewing duration for stereopsis and other variables affecting stereoacuity is unknown. The purposes of the study were to investigate the properties of normal temporal integration for stereoscopic vision with respect to the effects of contrast and spatial frequency of the stimuli and to determine whether the temporal summation of disparity is affected in deficient stereopsis caused by abnormal binocular vision during infancy. Psychophysical methods were used to measure stereothresholds in human and monkey subjects with either normal binocular vision or abnormal binocular vision. The results showed that the critical viewing duration for stereoscopic depth discrimination was independent of variations in basic stimulus parameters and/or the subject's stereoacuity. A critical duration of approximately 100 ms was found for both local (narrowband Gabor and broadband line targets) and global (dynamic random dots) stimuli. Although stereothresholds increased with decreasing stimulus contrast, the properties of temporal integration did not. Stereothresholds were substantially elevated for monkeys and humans with abnormal binocular vision, but the critical durations for these subjects were not significantly different from those of subjects with normal binocular vision. Overall, the results demonstrate that the general properties of temporal integration for stereopsis are similar to other detection and discrimination tasks that do not require binocular processing. In addition, increased integration time does not account for the elevated stereothresholds of subjects with abnormal binocular vision.

Vertical strabismus in monofixation syndrome

PURPOSE

The manifest angle of the horizontal deviation in monofixation syndrome (MFS) has been reported to reach a maximum of 8 to 10 PD. Review of the literature, however, revealed no studies about the vertical deviation associated with MFS. The purpose of this study is to evaluate the range of the angle of the vertical deviation in MFS.

METHODS

Forty patients who had MFS with vertical strabismus in the distance primary position were included in this study. All fulfilled the criteria for monofixation, fusing Worth 4 dots at near but suppressing at distance and/or having stereoacuity between 3000 and 60 seconds of arc by using Titmus stereotest and a horizontal deviation within 8 PD of orthophoria by simultaneous prism and cover test. Patients were divided into 3 groups: patients with hypertropia without any dissociated vertical deviation (DVD) (group I), patients with only DVD (group II), and patients with both hypertropia and DVD (group III).

RESULTS

Eighteen patients (45.0%) had hypertropia only (group I), 15 (37.5%) had DVD only (group II), and 7 (17.5%) had both (group III). In groups I and III the angle of hypertropia by simultaneous prism and cover test was 2 to 6 PD (mean, 3.9 PD) and in group II and III the angle of DVD was 4 to 14 PD (mean, 7.5 PD) at distance.

CONCLUSIONS

These results suggest that in MFS the angle of hypertropia can range up to a maximum of 6 PD. However, monofixation was observed in patients with a larger absolute angle of DVD (up to 14 PD), possibly due to an intermittent nature of the DVD.

Microtropia versus bifoveal fixation in anisometropic amblyopia

Microtropia with identity is a unique condition in which amblyopes have parafoveal eccentric fixation in the amblyopic eye in either monocular or binocular viewing, plus a macular scotoma. The condition has previously been described in anisometropic amblyopia. The records of 55 consecutively presenting anisometropic amblyopes were scrutinised and the cases divided into microtropes or non-microtropes (bifoveal fixators). The features of the two groups were then compared to identify factors associated with microtropia and to determine whether microtropes or bifoveal patients responded better to amblyopia therapy. Results show that 45% of anisometropic amblyopes have microtropia rather than bifoveal fixation. There appears to be no association between the microtropic phenomenon and age, depth of amblyopia or amount of anisometropia. Bifoveal patients may respond better to amblyopia therapy although the difference between groups was not great. The sensitive period during which amblyopia may be treated is the same for each group.

Testing stereopsis in the preschool child: is it clinically useful?

The evaluation of stereoacuity should provide an unambiguous assessment of binocular function in infants and young children. Unfortunately, clinical measures of stereopsis in these young patients often result in stereotheresholds poorer than the criteria suggested to differentiate normal from anomalous binocular vision. Thus, two experiments were conducted to determine whether the large stereothresholds frequently demonstrated on tests designed for young children are diagnostic of normal binocular function in preschool children. The first experiment investigated the salience of the monocular cues in the Lang and Frisby stereotests in normal preschool children (2 to 5 years old). None of the children who passed either the Frisby or the Lang stereotest under binocular conditions were able to pass either test monocularly, even after passing the test binocularly. In the second experiment, preschool children with abnormal binocular vision were tested with the Lang and Frisby stereotests to determine if large disparities (730 to 800 seconds of arc [arcsec]) could be passed without normal binocular vision. None of the children with strabismus passed either stereotest. However, two children with anisometropia passed the Frisby test and one of these children also passed the Lang test. These results suggest that in the absence of other clinical findings to the contrary, the demonstration of gross stereopsis with either the Frisby (730 arcsec) or Lang (733 or 800 arcsec) test in the preschool child implies normal binocular function. Thus, clinical tests of stereopsis for infants and preschool children, like those used routinely for adults, can provide evidence of binocular function without approaching stereothreshold.

Congenital esotropia with a bifixation result. Report of a case

Surgical alignment of the eyes in congenital esotropia within the first two years of age can result in the development of binocular vision. With one exception, reported here, the binocular vision has been extramacular and never macular. In this one case the patient was proven to be a bifixator. This is such an unusual outcome that the diagnosis of congenital esotropia must be questioned. Moreover, dissociated double hypertropia was not found in this case.

Sensorial anomalies in strabismus. (suppression, anomalous correspondence, amblyopia)

Some concepts regarding suppression, anomalous correspondence and amblyopia are revised according to the sensorial findings obtainable from esotropic patients directly in casual seeing (with the aid of the striated glasses test) and by grading a sensorial dissociating effect (with the aid of a bar of optical filters). The following points are emphasized: 1. Suppression appears to be minimal in small angle strabismus where diplopia seems mainly to be avoided by an anomalous correspondence mechanism. On the contrary, suppression is the prevalent mechanism in large angle strabismus. 2. The anomalous correspondence mechanism may lead to a weak type of anomalous binocular vision which is easily interrupted by light optical filters or by dissociating tests. 3. The subjective space of patients with anomalous binocular vision resembles that of normal binocular vision in some aspects. 4. The development of amblyopia is interpreted in the light of these new concepts on suppression and anomalous binocular vision. 5. Postoperatively, anomalous correspondence rapidly re-adapts to the smaller angle deviation and may normalize if the deviation is completely eliminated. This is evident only in casual seeing; for a certain time, dissociating tests reveal the preoperative correspondence status. This behaviour of correspondence in casual seeing has led to attempts at normalizing anomalous correspondence by prism therapy. Newly observed sensotio-motorial obstacles, however, have been found to frequently hamper treatment in casual seeing.