Prediction and Control of Slip-Free Rotation States in Sphere Assemblies.

We study fixed assemblies of touching spheres that can individually rotate. From any initial state, sliding friction drives an assembly toward a slip-free rotation state. For bipartite assemblies, which have only even loops, this state has at least four degrees of freedom. For exactly four degrees of freedom, we analytically predict the final state, which we prove to be independent of the strength of sliding friction, from an arbitrary initial one. With a tabletop experiment, we show how to impose any slip-free rotation state by only controlling two spheres, regardless of the total number.

Usage leading to an abrupt collapse of connectivity.

Network infrastructures are essential for the distribution of resources such as electricity and water. Typical strategies to assess their resilience focus on the impact of a sequence of random or targeted failures of network nodes or links. Here we consider a more realistic scenario, where elements fail based on their usage. We propose a dynamic model of transport based on the Bak-Tang-Wiesenfeld sandpile model where links fail after they have transported more than an amount µ (threshold) of the resource and we investigate it on the square lattice. As we deal with a new model, we provide insight on its fundamental behavior and dependence on parameters. We observe that, for low values of the threshold due to a positive feedback of link failure, an avalanche develops that leads to an abrupt collapse of the lattice. By contrast, for high thresholds the lattice breaks down in an uncorrelated fashion. We determine the critical threshold µ* separating these two regimes and show how it depends on the toppling threshold of the nodes and the mass increment added stepwise to the system. We find that the time of major disconnection is well described with a linear dependence on µ. Furthermore, we propose a lower bound for µ* by measuring the strength of the dynamics leading to abrupt collapses.

A binocular iPad treatment for amblyopic children.

PURPOSE: Monocular amblyopia treatment (patching or penalization) does not always result in 6/6 vision and amblyopia often recurs. As amblyopia arises from abnormal binocular visual experience, we evaluated the effectiveness of a novel home-based binocular amblyopia treatment. METHODS: Children (4-12 y) wore anaglyphic glasses to play binocular games on an iPad platform for 4 h/w for 4 weeks. The first 25 children were assigned to sham games and then 50 children to binocular games. Children in the binocular group had the option of participating for an additional 4 weeks. Compliance was monitored with calendars and tracking fellow eye contrast settings. About half of the children in each group were also treated with patching at a different time of day. Best-corrected visual acuity, suppression, and stereoacuity were measured at baseline, at the 4- and 8-week outcome visits, and 3 months after cessation of treatment. RESULTS: Mean (±SE) visual acuity improved in the binocular group from 0.47±0.03 logMAR at baseline to 0.39±0.03 logMAR at 4 weeks (P<0.001); there was no significant change for the sham group. The effect of binocular games on visual acuity did not differ for children who were patched vs those who were not. The median stereoacuity remained unchanged in both groups. An additional 4 weeks of treatment did not yield additional visual acuity improvement. Visual acuity improvements were maintained for 3 months after the cessation of treatment. CONCLUSIONS: Binocular iPad treatment rapidly improved visual acuity, and visual acuity was stable for at least 3 months following the cessation of treatment.

Longitudinal changes in refractive error of children with infantile esotropia.

AIM: the aim of this study was to quantify changes in refractive status over time in children with infantile esotropia (ET) and to analyse a number of clinical factors associated with infantile ET to determine how they may affect emmetropisation. METHODS: longitudinal cycloplegic refraction data were collected for 5-12 years from 143 consecutive children enroled in a prospective study of infantile ET by 6 months of age. Changes in refractive error with age were summarised with descriptive statistics and the influence of amblyopia, undercorrection of hypermetropia, accommodation, and binocular factors on emmetropisation were evaluated by analysis of variance and t-tests. RESULTS: most had low to moderate hypermetropia on the initial visit (55% had <+3.00 D). Although the initial refractive error is similar to normative data, the rapid decrease in hypermetropia that characterises normal development during the first 9 months of life is absent in children with infantile ET. After 9 months of age, children with infantile ET follow a developmental course, which is similar to the normative course; there is little change in hypermetropia during years 1-7, followed by a decline of approximately -0.5 D/year beginning at age 8 years. None of the clinical factors examined had a statistically significant effect on the course of refractive changes with age. CONCLUSION: children with infantile ET exhibit a different pattern of refractive development than that seen in normative cohorts. The long-term changes in refraction observed in children with infantile ET suggest that there is a need for long-term clinical follow-up of these children.

Re-recession of the medial rectus muscles in patients with recurrent esotropia.

PURPOSE: Retrospective evaluation of changes in ocular motility after surgical re-recession of the medial rectus (MR) muscles as treatment of recurrent esotropia (ET). METHODS: We describe 115 patients (age, 11 months-77 years; median, 11.1 years; 83 children and 32 adults) with an average amount of non-accommodative ET before surgery of 18.7 PD (SD = 8.8 PD). Preoperative alignment, amount of re-recession, distance from insertion to the limbus, and postoperative alignment and versions were collected. RESULTS: In most cases, MR muscles were re-recessed to a fixed distance of 12 mm from the limbus, with unilateral re-recessions in cases with relatively small ET (typically < 20 PD) and bilateral re-recessions in cases with larger amounts of ET (typically > 20 PD). No clear relation was found between the amount of re-recession and the change in alignment in prism diopters. The success rate (esotropia [ET] < or = 10 PD or exotropia [XT] < or = 8 PD) 4 weeks to 8 months after surgery was 85%, with 4 patients still showing ET and 13 patients showing XT. Incidence of XT was higher for bilateral than for unilateral re- recessions. Significant underaction of the MR muscles was noted in 7% of the patients. None of the undercorrected patients and only 1 of the overcorrected patients were adults. Among adults, incidence of MR underaction was 4%. Long-term follow-up (8-120 months; median, 25 months) data from 59 patients indicated that good stability in alignment can be expected. CONCLUSION: The results support the notion that MR re-recession to 12 mm from the limbus successfully corrects recurrent ET up to 35 PD and that it is particularly effective in adults.

Costenbader lecture. Anatomy and surgery of the inferior oblique muscle: recent findings.

BACKGROUND: Surgery of the inferior oblique muscle (IO) has undergone significant changes in the past 160 years. Many investigators have contributed to our understanding of the action of this muscle and to the surgical options that have developed. This article reviews the history of IO surgery with particular emphasis on the anterior transposition procedure. METHODS: Anatomic and physiologic studies on the neurofibrovascular bundle of the IO are presented. RESULTS: The ligamentous structure of the neurofibrovascular bundle of the IO provides the ancillary origin for the posterior temporal fibers of the IO when its insertion is transposed anteriorly. DISCUSSION: Recent anatomic findings have helped explain the effects of the anterior transposition procedure and allow further development of our surgical armamentarium for vertical strabismus problems. Further nasal transposition of that insertion should reduce or eliminate the incidence of the antielevation syndrome. If transposed far nasally, the IO could convert to an intorter, as well as to an antielevator and tonic depressor.

Early binocular visual experience may improve binocular sensory outcomes in children after surgery for congenital unilateral cataract.

PURPOSE: To compare the effect of intensive and reduced occlusion therapy regimens on binocular sensory outcomes, visual acuity, and the prevalence of strabismus in children after surgery for congenital unilateral cataract. METHODS: Two nonrandomized groups of patients were studied prospectively: (1) an intensive occlusion group (n = 29) patched 80% of waking hours were followed for a median 6.9 years and (2) a reduced occlusion group (n = 8) patched 25% to 50% of waking hours were followed for a median 4.3 years. Six subjects in the intensive group and 4 in the reduced occlusion group had secondary intraocular lenses. Two subjects in the intensive group had epikeratophakia surgery. Binocular sensory function was assessed with random dot and contour stereoacuity tests and the Worth 4-dot test. The prevalence and age at onset of strabismus were determined from the patients' charts. RESULTS: A higher proportion of subjects in the reduced occlusion group (50%) had stereoacuity or fusion compared with the intensive occlusion group (14%), a borderline significant difference (P =.08). No significant difference (P =.55) was found in median visual acuity between the intensive (20/50) and the reduced occlusion (20/55) groups. The 90% prevalence of strabismus in the intensive occlusion group was slightly higher than the 63% prevalence in the reduced occlusion group, although this difference was not significant (P =.18). CONCLUSIONS: These results suggest that a reduced occlusion protocol may be associated with better binocular sensory outcomes and a reduced prevalence of strabismus without compromising good visual acuity in children treated for congenital unilateral cataract.

Anterior and nasal transposition of the inferior oblique muscle: a preliminary case report on a new procedure.

PURPOSE: To describe this new extraocular muscle surgery. METHOD: Case Report of a child in need of treatment of a weak superior oblique muscle which, at surgery, was in fact found to be absent. After a prior only partially successful recession of the antagonist inferior oblique (IO), the IO muscle was detached and transposed to a new insertion in the inferior nasal quadrant converting the muscle, as a result of its functional origin being the neurovascular bundle ["Ligament of Stager"-ed], from an extorter and elevator of the globe to an intorter and depressor. RESULT: Satisfactory binocular alignment was achieved. CONCLUSION: This new surgical procedure provides significant advantages, and should be added to our surgical armamentarium.

Surgical management of V-pattern strabismus and oblique dysfunction in craniofacial dysostosis.

INTRODUCTION: Strabismus affects as many as 60% to 70% of patients with craniofacial dysostosis. V-pattern strabismus with severe oblique muscle dysfunction is the most common ocular motility problem seen and can be difficult to manage. Few studies have reported on the results of strabismus surgery in this condition. METHODS: We retrospectively reviewed the surgical management and outcomes of 14 patients with craniofacial dysostosis who underwent 16 operations to determine the optimal surgical procedure and to report on extraocular muscle anomalies noted at the time of surgery. Operations performed included medial rectus muscle infraplacement (n = 2), inferior oblique (IO) recession (n = 3), IO myectomy (n = 3), IO anterior transposition (n = 3), and IO denervation/extirpation (n = 5). RESULTS: All patients had significant residual ocular motility dysfunction postoperatively. No beneficial effect was noted after IO anterior transposition or after medial rectus muscle infraplacement. Modest improvement of the V-pattern and oblique muscle dysfunction was noted after denervation/extirpation and myectomy of the IO muscle. Bilateral absent or anomalous superior oblique tendons were noted in 8 of 9 patients in whom the superior oblique tendon was examined at surgery. CONCLUSIONS: Strabismus in craniofacial dysostosis is complex and difficult to cure with surgery. Denervation/extirpation and myectomy of the IO muscle offered modest benefits, though neither procedure resulted in normalization of ocular motility. Agenesis of the superior oblique tendon may be causally related in a large proportion of affected patients.

Screening for amblyopia in preverbal children with photoscreening photographs: II. Sensitivity and specificity of the MTI photoscreener.

OBJECTIVE: To determine the sensitivity and specificity of vision screening using the Medical Technology and Innovations (MTI), Inc., PhotoScreener. DESIGN: Cross-sectional study. PARTICIPANTS AND TESTING: Three hundred ninety-two children less than 4 years of age received a complete ophthalmologic examination and were photographed using the MTI PhotoScreener. One hundred three children had normal examinations, and the remaining 284 children had conditions of interest for pediatric screening: ptosis, media opacity, refractive error, or strabismus. Five children were excluded. MAIN OUTCOME MEASURES: The grading of the photographs by the manufacturer's representative was compared with the results of the ophthalmologic examinations. Sensitivity and specificity of vision screening were determined. RESULTS: The analysis of all informative photographs resulted in a sensitivity of 65% and a specificity of 87%. The sensitivity of detection for children with some forms of strabismus was high, up to 95% for esotropia of 10Delta or more. Sensitivities for the detection of ptosis, media opacity, and refractive error were poor in patients where strabismus was not also present. CONCLUSIONS: The MTI PhotoScreener may play a role in preverbal vision screening; identification of two of three children with amblyopiogenic factors before age 4 would be an exciting advance in public health. However, improvement in the ability to identify children with media opacity and refractive error is necessary. Improvements may be possible with modifications of the examination failure and photograph grading criteria.

Screening for amblyopia in preverbal children with photoscreening photographs. III. improved grading criteria for hyperopia.

OBJECTIVE: To examine the ability of the Medical Technology and Innovations (MTI), Inc., Photoscreener (Cedar Falls, IA) to detect hyperopia and to improve the photograph grading criteria to screen for amblyopiogenic levels of hyperopia. DESIGN: Cross-sectional study and reanalysis. PARTICIPANTS AND TESTING: In previous work, 392 participants received a complete ophthalmologic examination and were photographed using the MTI Photoscreener. For this study, all 209 participants with normal examination findings (65 children) or hyperopia without anisometropia (144 children) were selected. The data were reanalyzed using modified photograph grading and ophthalmologic examination failure criteria. Potential reasons for why many children with hyperopia passed photoscreening were explored. MAIN OUTCOME MEASURES: We determined whether a study participant would pass or fail screening with a given photograph grading and ophthalmologic examination failure criteria. RESULTS: Most children with hyperopia of +2.00 to +3.50 diopters (D) passed screening with the MTI instrument, in most cases because their photographs lacked bright crescents. When bright crescents in at least two of the four possible meridians were the grading guideline for screening failure and the pediatric ophthalmologists' consensus hyperopia failure criteria (> +3.50 D) were adopted, the sensitivity for hyperopia detection was 100% and the specificity was 88%. Identical results were obtained using the American Academy of Ophthalmology Preferred Practice Pattern hyperopia failure criteria (>/= +4.50 D). CONCLUSIONS: The MTI photograph grading guidelines can be simplified, and the ophthalmologic examination failure criteria for hyperopia can be improved. The presence of a bright crescent in the lower or the left pupillary margin indicate hyperopia in an amblyopiogenic range (> +3.50 D).

Co-development of VEP motion response and binocular vision in normal infants and infantile esotropes.

PURPOSE: To determine the maturational course of nasotemporal asymmetry in infantile esotropia and to define the relationships among the symmetry of the motion visual evoked potential (MVEP), eye alignment, fusion, and stereopsis. METHODS: Sixty healthy term infants and 34 infants with esotropia participated. Nasotemporal MVEP asymmetry was assessed by the presence of a significant F1 response component with an interocular phase difference of approximately 180 degrees and by an amplitude "asymmetry index." Fusion was evaluated using the 4 p.d. base out prism test. Random dot stereoacuity was assessed in infants with forced-choice preferential looking (FPL) using the Infant Random Dot Stereocards. Eye alignment was assessed by the alternate prism and cover or the modified Krimsky test. RESULTS: Normal infants 2 to 3 months of age exhibited marked nasotemporal MVEP asymmetry, which rapidly diminished by 6 to 8 months. Neonates did not exhibit MVEP asymmetry. There was good concordance between fusion and MVEP symmetry and between stereopsis and MVEP symmetry; the concordance between MVEP symmetry and orthoposition of the visual axes was significantly poorer. The same proportion of normal and young esotropic infants showed symmetrical MVEPs. Regardless of the age at surgery, most patients with infantile esotropia had asymmetrical MVEPs after surgery. CONCLUSIONS: These data support a strong link between fusion and MVEP symmetry during both normal maturation and in infantile esotropia. Furthermore, the finding that the youngest infants with esotropia do not differ significantly from normal suggests that the nasotemporal asymmetry found in older patients with infantile esotropia does not represent an arrest of maturation but, rather, a pathologic change of the motion pathways.

Why does early surgical alignment improve stereoacuity outcomes in infantile esotropia?

PURPOSE: Recent studies of infantile esotropia suggest that early surgical alignment may enhance stereopsis and that alignment during the first 6 months of life may be optimal. Early surgery both establishes alignment during an early critical period for the development of stereopsis and minimizes the duration of misalignment. Here we examine the role of these 2 factors in promoting improved stereopsis outcomes. METHODS: Participants were 129 consecutive patients enrolled in a prospective study of infantile esotropia who were followed up for a minimum of 5 years. At ages 5 to 9 years, Randot stereopsis was evaluated. RESULTS: Multiple linear regression indicated that duration of misalignment, but not age at alignment or age at onset, was a significant factor in determining random dot stereopsis outcomes. Moreover, patients with stereopsis were less likely to have a loss of horizontal eye alignment requiring surgery than patients without stereopsis (14% versus 32%; z = 1.96, P =.05). Patients with stereopsis were also less likely to have dissociated vertical deviation than patients without stereopsis (25% versus 63%; z = 3.36, P <.001). CONCLUSIONS: The results suggest that early surgical alignment is associated with better stereopsis in those patients with infantile esotropia who were treated during the first 24 months of life, because early surgery minimizes the duration of misalignment, not because alignment is achieved during an early critical period of visual maturation. Random dot stereopsis can also be achieved in patients with alignment provided that the duration of misalignment is not prolonged. Improved outcomes of random dot stereopsis are associated with more stable long-term alignment outcomes.

Long-term results of silicone expander for moderate and severe Brown syndrome (Brown syndrome "plus").

BACKGROUND: The treatment of Brown syndrome has been undergoing an evolution toward more effective procedures with fewer operative interventions. Dr Kenneth Wright has introduced a procedure of superior oblique muscle tenotomy with a silicone expander to reduce the incidence of overcorrection. METHODS: There was a retrospective study of 20 eyes of 19 consecutive patients with moderate or severe Brown syndrome (Brown syndrome "plus"). Follow-up ranged from 12 to 72 months. The expander, which varies 6 to 10 mm in length, was placed in all patients in the tenotomized superior oblique muscle tendon 5 mm nasal to the nasal border of the superior rectus muscle using 7-0 or 8-0 Prolene suture without violating the inner layer of the intermuscular septum. The intermuscular septum was closed over the silicone expander. RESULTS: One hundred percent of patients had resolution of the down shoot in adduction and some or full ability to elevate the eye in adduction. Twenty percent of patients required reoperation (12.5% using 5-8 mm expanders) for overcorrection. Restriction of downgaze was not seen postoperatively. Patients often show an undercorrection 1 to 6 months postoperatively and improve or occasionally overcorrect at 1 to 2 years postoperatively. One patient with a 10-mm expander extruded the implant. DISCUSSION: Placement of a 5- to 8-mm silicone expander in the tenotomized superior oblique muscle tendon is an effective means of correcting Brown syndrome with a low rate of reoperation. Initial undercorrection should not discourage the surgeon because improvement may continue for up to 3 years. The goal of treatment should be to convert a moderate or severe Brown syndrome (Brown syndrome plus) to a mild Brown syndrome ("true" Brown syndrome). CONCLUSION: This technique reduces the need for either simultaneous or subsequent inferior oblique muscle weakening and represents an advance in the treatment of Brown syndrome.

A value analysis model applied to the management of amblyopia.

PURPOSE: To assess the value of amblyopia-related services by utilizing a health value model (HVM). Cost and quality criteria are evaluated in accordance with the interests of patients, physicians, and purchasers. METHODS: We applied an HVM to a hypothetical statistical ("median") child with amblyopia whose visual acuity is 20/80 and to a group of children with amblyopia who are managed by our practice. We applied the model to calculate the value of these services by evaluating the responses of patients and physicians and relating these responses to clinical outcomes. RESULTS: The consensus value of care for the hypothetical median child was calculated to be 0.406 (of 1.000). For those children managed in our practice, the calculated value is 0.682. Clinically, 79% achieved 20/40 or better visual acuity, and the mean final visual acuity was 0.2 logMAR (20/32). Value appraisals revealed significant concerns about the financial aspects of amblyopia-related services, particularly among physicians. Patients rated services more positively than did physicians. CONCLUSIONS: Amblyopia care is difficult, sustained, and important work that requires substantial sensitivity to and support of children and families. Compliance and early detection are essential to success. The value of amblyopia services is rated significantly higher by patients than by physicians. Relative to the measured value, amblyopia care is undercompensated. The HVM is useful to appraise clinical service delivery and its variation. The costs of failure and the benefits of success are high; high-value amblyopia care yields substantial dividends and should be commensurately compensated in the marketplace.

Early treatment of congenital unilateral cataract minimizes unequal competition.

PURPOSE: Dense congenital unilateral cataracts may compromise visual development through visual deprivation and biased interocular competition, whereas dense congenital bilateral cataracts compromise visual development primarily through visual deprivation alone. Differences in sensory deficits between the two patient groups with these disorders may reflect the specific effects of unequal competition. To determine whether early treatment (at <8 weeks of age) minimizes the adverse effects of unequal competition, grating acuity deficits during the immediate posttreatment period and contrast sensitivity deficits at 6 to 8 years of age were assessed in 29 children with histories of dense congenital unilateral or bilateral cataracts who had had treatment between 1 and 8 weeks or 12 and 30 weeks. All children maintained good to excellent compliance with optical correction and occlusion therapy. METHODS: Grating acuity was measured using a two-alternative forced-choice preferential-looking staircase protocol. Contrast thresholds at three spatial frequencies (0.38, 1.5, and 6 cyc/deg) were measured at each of two temporal frequencies (2- and 8-Hz sinusoidal counterphase modulation) using D6 grating patches. RESULTS: Grating acuity deficits in the immediate posttreatment period were similar in patients with a history of unilateral cataract (n=10) and those with a history of bilateral cataracts (n=6) when treatment was provided during the first 8 weeks of life. With later treatment, patients with a history of unilateral cataract (n=7) had significantly larger grating acuity deficits than patients with a history of bilateral cataracts (n=6). Children with a history of dense congenital unilateral cataract had similar deficits in contrast sensitivity to children with a history of bilateral cataracts when treatment was initiated during the first 8 weeks of life. When treatment was initiated later (i.e., at 12-30 weeks), patients with a history of unilateral cataract showed greater deficits in contrast sensitivity and a dependence of the amount of spatial contrast sensitivity deficit on temporal frequency than did patients with a history of bilateral cataracts. CONCLUSIONS: These findings support the hypothesis that only visual deprivation is active as an amblyogenic factor during the first weeks of life, but when unilateral deprivation is prolonged to 12 to 30 weeks, unequal competition also plays a role in amblyogenesis.

Screening for amblyopia in preverbal children with photoscreening photographs. National Children's Eye Care Foundation Vision Screening Study Group.

OBJECTIVE: This study aimed to determine the ability of healthcare professionals and lay volunteers to grade photoscreening photographs. DESIGN: The study design was a cross-sectional study. PARTICIPANTS AND INTERVENTION: One hundred children 3 years of age or younger received a complete ophthalmologic examination and were photographed using the Medical Technology Innovations (MTI) photoscreener. Twenty-six children had normal examination results, and the remaining 74 children had conditions that are of interest for pediatric screening, including strabismus, refractive error, media opacities, and ptosis. Eighteen volunteers, including pediatric ophthalmologists, pediatricians, ophthalmic technicians, health department nurses, Prevention of Blindness Society personnel, and Lions Club volunteers, graded each of the 100 photoscreening photographs. MAIN OUTCOME MEASURES: Sensitivity and specificity of vision screening and of photograph grading were measured. RESULTS: Results from various graders yielded sensitivities ranging from 37% to 88% and specificities ranging from 40% to 88%. No single grader achieved sensitivity and specificity both greater than 70%. The grading of the manufacturer's representative had a sensitivity of 43% and a specificity of 85%. Sensitivity decreased to 31% for strabismus and 18% for refractive error when the correct type of strabismus or refractive error was required to be considered true-positives. Results were not positively correlated with the ophthalmologic knowledge of the participant. CONCLUSIONS: The wide variability in sensitivities and specificities among graders indicates inconsistent photograph interpretation skills or deficient screening guidelines or both. For off-axis photoscreening as implemented by the MTI system to become a useful vision-screening method, additional photograph interpretation skill transfer may be beneficial, although not necessarily sufficient.

The natural history of infantile esotropia during the first six months of life. Pediatric Eye Disease Investigator Group.

PURPOSE: The present study addresses the natural history ocular alignment in infantile esotropia that presents at 2 to 4 months of age. METHODS: Eye alignment during the first 6 months of life was evaluated in two cohorts of healthy infants who initially had esotropia at 2 to 4 months of age; 80 infants were enrolled in a prospective study at the Retina Foundation of the Southwest (RFSW), and 41 infants were reviewed retrospectively as a pilot study for the Early Surgery for Congenital Esotropia (ESCET) multicenter trial. In addition, 79 of the 80 children in the RFSW cohort were reexamined at 4.5 years of age or older for ocular alignment and stereopsis. RESULTS: Among infants who initially had constant esotropia > or = 40 PD, 0 of 45 children in the RFSW cohort and 0 of 21 children in the ESCET cohort showed resolution to orthophoria. In addition, only 2 infants showed a reduction in angle of deviation below 40 PD (one to 35 PD and one to 20 PD). Resolution to orthophoria was noted in a few infants who initially had small angle or variable angle esotropia. On follow-up at 4.5 years of age or greater, 91% of the children in the RFSW cohort had alignment within 8 PD of orthoposition and 30% had stereoacuity of 3000" to 60". Children who underwent surgical alignment at 6 months of age had a higher prevalence of coarse stereopsis than children who underwent alignment at 7 to 15 months of age. CONCLUSIONS: Taken together, these results suggest that infants who present at 2 to 4 months of age with constant esotropia of 40 PD or greater are valid candidates for surgical treatment. In addition, data from long-term follow-up support the hypothesis that early surgical alignment may promote the development of at least coarse stereopsis in these infants.