Effects of strabismus surgery on corneal topography

Corneal tomography changes following major (6 mm) medial rectus muscle recession: a prospective cohort study using Pentacam®

INTRODUCTION

The aim of this study is to evaluate changes in corneal astigmatism, axial anterior corneal curvature, as well as changes in the anterior chamber depth and central corneal thickness, 2 months following the unilateral recession of medial rectus muscle in children.

METHODS

Thirty-three children with esotropia were prospectively evaluated following unilateral medial rectus muscle recession, using Pentacam®. Comparisons were made between the operated and fellow unoperated eyes, pre, and postoperatively. The assessment was made for changes in the radius of axial curvature on major meridians at 3 and 3.5 mm from the optical corneal center in the mid-peripheral zone. Astigmatism changes of the anterior and posterior corneal surface were calculated using vector analysis software (astigMATIC®). ANOVA model was used to examine the interaction between age or central corneal thickness and postoperative changes in anterior and posterior surface corneal astigmatism.

RESULTS

In the intervention group, changes in anterior and posterior corneal surface astigmatism were statistically significant, with a mean increase of 0.59Dx92 and 0.08Dx91, respectively. In the mid-peripheral corneal zone, there is an increase in the radius of anterior corneal axial curvature more evident nasally 3.5 mm from the corneal center on the horizontal meridian, with corresponding decrease superiorly and inferiorly at 3 and 3.5 mm from the corneal center on the vertical meridian.

DISCUSSION

The changes in total astigmatism of the operated eyes are mainly attributed to the anterior corneal surface. These changes are associated with flattening in the 180 meridian of the cornea, leading to a shift to "with-the-rule" astigmatism.

Refractive changes after strabismus surgery in patients with intermittent exotropia

OBJECTIVES

To evaluate the long-term refractive changes after horizontal muscle surgery in patients with intermittent exotropia and investigate the correlation between changes in the postoperative refractive error and clinical factors.

METHODS

We retrospectively reviewed the clinical data of patients aged < 15 years who underwent unilateral strabismus surgery (lateral rectus recession and medial rectus resection [RR, n = 47], lateral rectus recession and medial rectus plication [RP, n = 81], or lateral rectus recession [LRc, n = 68]). Preoperative and postoperative refractive errors up to four years after surgery were recorded. A mixed model was applied to compare the refractive error between the operated and fellow eyes and identify the factors associated with postoperative refractive changes.

RESULTS

The mean age at surgery was 7.5±2.4years, and girls accounted for 56.1% of the study population. There was no significant difference in the change in the spherical equivalent of refractive error between both eyes throughout the postoperative period. In contrast, the operated eyes consistently and significantly showed higher cylindrical power in with-the-rule astigmatism by 0.25D than in fellow eyes. Age, sex, and preoperative refractive error were not correlated with changes in postoperative astigmatism. Meanwhile, the type of surgery showed a significant interaction with the astigmatism changes. RP had less effect on the changes in astigmatism than RR and LRc (p = 0.001 and p = 0.022, respectively).

CONCLUSIONS

Horizontal muscle surgery has no long-term effect on the change in the spherical equivalent. However, mild with-the-rule astigmatism is induced and sustained after surgery, and the type of surgery affects the postoperative change of astigmatism.

Long-term astigmatism changes following horizontal muscle recession: a prospective cohort study

Strabismus surgery may cause refractive changes, particularly in astigmatism. The aim of this study is to evaluate those changes in astigmatism two and 12 months following unilateral recession of horizontal rectus muscles in children. The authors prospectively evaluated 66 children with esotropia or exotropia, that would undergo a unilateral recession strabismus surgery. Comparisons were made between the 66 eyes that would undergo strabismus surgery and the fellow unoperated 66 eyes of the same children. The 66 eyes that would undergo strabismus surgery were divided into medial (38 eyes) and lateral (28 eyes) rectus muscle subgroups, and further, into subgroups based on the astigmatism axis preoperatively (with-the-rule astigmatism: 35 eyes, no astigmatism: 20 eyes, oblique astigmatism: 10 eyes, against-the-rule astigmatism: 1 eye). All patients were examined one day preoperatively, and then, two and 12 months postoperatively. Paired tests were conducted, and the significant level was set to 0.05 or was adjusted for subgroups. Mean age of children included was 6.73 years (SD = 3.19). Mean astigmatism values preoperatively, 2 and 12 months postoperatively were 0.92D (SD = 0.95), 1.45D (SD = 1.04) and 1.50D (SD = 1.10), respectively, for the eyes that underwent strabismus surgery. A statistically significant mean increase of 0.58D in astigmatism values in the eyes that underwent strabismus surgery was observed 12 months postoperatively (p < .005). Astigmatism values in the eyes that did not undergo strabismus surgery did not statistically significantly change during the observation period. The increase of the absolute values of astigmatism in medial and lateral rectus muscle subgroups was similar, 0.59D (SD = 0.10) and 0.57D (SD = 0.11), respectively. For the eyes that had with-the-rule astigmatism and no astigmatism preoperatively, a statistically significant increase was shown 12 months postoperatively (0.64D and 0.66D respectively) (p < .005). Changes in astigmatism were observed in the eyes which underwent recession of horizontal rectus muscles compared to the fellow eyes, which did not undergo any intervention. An increase in cylindrical power was noted in the eyes that had with-the-rule and no astigmatism prior to surgery. This increase may be interpreted by the decreased tension of the recessed rectus muscle following strabismus surgery. Decreased forces, caused by the recessed horizontal rectus muscle, acting on the sclera on 180-degree meridian may lead to corneal flattening on this particular meridian and consequently, a corneal steepening on the 90-degree meridian. These changes seem to be stable during the first 12 postoperative months.

Alterations of lower- and higher-order aberrations after unilateral horizontal rectus muscle surgery in children with intermittent exotropia: A retrospective cross-sectional study

Background

This retrospective, cross-sectional study investigated changes in corneal lower- and higher-order aberrations that cause visual disturbance after lateral rectus recession and medial rectus resection in children.

Methods

Eighty-five eyes of 85 patients (44 boys; 8.64±2.88 years) who underwent lateral rectus recession and medial rectus resection to correct intermittent exotropia were assessed. The Galilei G4 Dual Scheimpflug Analyzer was used for wavefront analysis. Risk factors (age, sex, amount of surgery, preoperative axial length, preoperative intraocular pressure) were determined. Outcome measures included simulated and ray-tracing mode keratometry with secondary defocus, oblique, and vertical astigmatism (for lower-order aberrations) and the root mean square, 3^rd-order vertical and horizontal coma, oblique and horizontal trefoil, 4^th-order spherical aberration, oblique and vertical secondary astigmatism, and oblique and vertical quadrafoil (2^nd‒8^th sums) (for higher-order aberrations).

Results

Myopic with-the-rule changes in low-order aberrations and increases in simulated and ray-tracing mode keratometry during the 3 months following lateral rectus recession and medial rectus resection were attributed to muscle healing and stability changes. High-order aberrations altered in the week following surgery almost returned to normal within 3 months. Axial length, the amount of surgery, age, and sex affected astigmatism due to differences in patients’ scleral states.

Conclusions

Clinicians should consider changes in high-order aberrations of young individuals who underwent lateral rectus recession and medial rectus resection and may not be able to verbalize changes in vision.

[Comparative analysis of refractive and topographic changes after eye muscle surgery]

Hintergrund

Über die Frage, ob nach Augenmuskeloperationen Refraktions- oder Topographieveränderungen zu erwarten sind, besteht weitestgehend Unklarheit.

Material und Methoden

In der vorliegenden Studie wurden prä- sowie postoperativ von 229 Augen objektive Refraktion, Pentacam (Fa. Oculus, Menlo Park, CA, USA) und Visus erhoben und analysiert. Die Untersuchung erfolgte präoperativ, am ersten postoperativen Tag sowie nach 3 Monaten.

Ergebnisse

Nach Operationen an einem sowie 2 geraden Augenmuskeln bestehen signifikante Veränderungen des Astigmatismus (p < 0,001), jedoch normalisiert sich dieser nach 3 Monaten wieder auf das präoperative Niveau. Ebenso war dieser Verlauf nach kombinierten Operationen von geraden und schrägen Augenmuskeln zu belegen.

Schlussfolgerung

Es lässt sich daher postulieren, dass eine umfangreiche Aufklärung von Patienten hinsichtlich passagerer Veränderungen des Zylinders insbesondere bei Beteiligung gerader Augenmuskeln unabdingbar ist und postoperativ eine ergänzende Refraktions- und Topographiekontrolle bei mangelnder Visusrehabilitation sinnvoll sein kann.

Age-Related Changes in Astigmatism and Potential Causes

Astigmatism causes deterioration of the retinal image and affects vision quality. Maintenance and improvement of visual function requires an understanding of the prevalence, age-related changes, and mechanisms of astigmatism. In this article, we discuss the findings of studies that investigated astigmatism. Some of these studies showed that the prevalence of high degrees of astigmatism in childhood typically decreases with emmetropization. With-the-rule astigmatism occurs most commonly in young adults. With age, the prevalence of astigmatism increases, and the axis shifts from a predominance of with-the-rule astigmatism to a predominance of against-the-rule astigmatism. This age-related change is caused by alterations in corneal curvature. Although the cause of this change is not fully understood, alterations in the position and tension of the eyelid, corneal stromal collagen fibrils, Descemet membrane, and extraocular muscles may influence the shape of the cornea. Furthermore, genetic factors may contribute to the development of astigmatism. Technological advances in ophthalmology are expected to improve our understanding of the etiology of astigmatism and enable the maintenance of quality of vision.

The Effect of Strabismus Muscle Surgery on Corneal Biomechanics

Purpose

Studying the early effect of different extraocular muscle (EOM) surgeries on corneal biomechanics.

Subjects and methods

This is a prospective, nonrandomized, interventional study, in which 42 eyes of 29 candidates for EOM surgery for strabismus correction at Cairo university hospitals, aged 14–37 years, were recruited. All participants had measuring of the visual acuity, refraction (spherical equivalent (SE)), assessment of the EOM motility and muscle balance, sensory evaluation, fundus examination, and assessing the ocular biomechanics using the Ocular response analyzer (ORA, Reichert, INC., Depew, NY) noting the corneal hysteresis (CH) and corneal resistance factor (CRF) preoperatively. Same patients were reassessed using ORA 4 weeks postoperatively following a different standard EOM surgery (recti weakening/strengthening and inferior oblique weakening either (graded recession) according to the surgical indication, and ∆CH and ∆CRF were calculated, each is the preoperative − the postoperative value.

Results

∆CH and ∆CRF = −0.78 ± 1.56 and −0.72 ± 2.15, respectively, and a highly significant difference was found between each of the pre- and postoperative CH and CRF (p < 0.001). 18 eyes had single EOM surgery, while 24 had multiple (2 or 3) EOM surgery; ∆CH in the single group = −1.28 ± 1.5, and ∆CH in the multiple group = 0.4 ± 1.49 (p=0.07). 23 eyes had EOM weakening surgery, while 18 had combined weakening and strengthening EOM surgery: ∆CH in the weakening group = −1.24 ± 1.77 and ∆CH in combined group = −0.26 ± 1.07 (p=0.04). A nonsignificant difference was found for ∆CRF (p=0.53).

Conclusion

A different EOM surgery has an early tendency for increase of the postoperative CH specially for muscle weakening procedures (recti recession/inferior oblique muscle weakening).

Changes of corneal topographic measurements and higher-order aberrations after surgery for exotropia

Purpose

To analyze changes in corneal topographic measurements and higher-order aberrations (HOAs) after horizontal muscle surgery for exotropia.

Design

Retrospective, observational study.

Methods

A total of 131 eyes of 121 patients who had undergone surgery for exotropia were included. The eyes with unilateral lateral rectus (ULR) or bilateral lateral rectus (BLR) recession(s) were assigned to group A, and those with unilateral lateral rectus recession & medial rectus resection (R&R) to group B. Corneal topographic measurements and HOAs were compared between the preoperative and postoperative periods using a Placido-dual Scheimpflug analyzer (Galilei 2^TM, Ziemer, Port., Switzerland) for each group.

Results

In group A, simulated keratometery (sim K) was significantly changed until 3 months postoperatively relative to the preoperative value (postoperative 1 week, p = 0.017; 1 month, p = 0.037; and 3 months, p = 0.023, respectively). All steep K (steep sim K, steep-Kpost, and TCP-steep K) parameters also were significantly changed at postoperative 1 month (p<0.001, p = 0.015, p<0.001, respectively), but not at 3 months. Among the higher-order aberrations, spherical aberration (Z₄⁰) and secondary horizontal astigmatism (Z₄²) at postoperative 1 week had significantly changed from the preoperative values, as had horizontal quadrafoil (Z₄⁴) at 1 month. However, in group B, only vertical quadrafoil (Z₄^-4) showed statistically significant changes, at postoperative 1 and 3 months. None of the other postoperative parameters was significantly different from the corresponding preoperative value.

Conclusion

Lateral rectus recession induced changes in both corneal topographic measurements and HOAs, whereas R&R did so only in HOAs. These changes might explain some patients' complaints about poor quality of vision.

Comparison of Preoperative and Postoperative Anterior Segment Measurements with Pentacam in Horizontal Muscle Surgery

Purpose

To evaluate the effect of horizontal muscle surgery (recession or recession plus resection) on the anterior chamber parameters in patients after strabismus surgery. Patients and Methods. The Scheimpflug of 18 eyes of 12 patients with horizontal deviations were recorded just before surgery and 1 month after surgery. The power of anterior surface of cornea in horizontal and vertical axis, thinnest corneal thickness, anterior chamber depth, anterior chamber volume, and cornea volume were analyzed. The clinical characteristics of patients, the size of the deviations, the surgical doses, and observed responses to surgery were reviewed.

Results

There were six male and six female patients with an average age of 11.4 years (range, 4 to 22 years). Mean preoperative deviation was 47.91 PD (range, 20 to 75 PD), eight patients had esotropia with 57.5 PD average deviation (range, 40 to 75 PD), and four patients had exotropia with 28.75 PD average deviation (range, 20 to 35 PD). Of these 18 eyes, 12 eyes had horizontal muscle recession and 6 eyes had recession plus resection surgery. At the end of 1 month, three patients were orthophoric and eight patients had residual deviations varying between 16 and 35 PD. Preoperative and postoperative comparison of the whole study group documented insignificant changes in anterior chamber parameters and in keratometer readings. However, after dividing patients into two groups–recession or recession plus resection group–only one parameter, anterior chamber volume, was significantly reduced in recession plus resection group.

Conclusions

Patients with strabismus who undergo recession plus resection procedure are prone to change in anterior chamber volume. Study with larger groups and long follow-up is necessary for clearer documentation of alterations at anterior chamber parameters.

A paired comparison study on refractive changes after strabismus surgery

PURPOSE

To quantify refractive changes following horizontal lateral rectus recession and medial rectus resection surgery and to investigate the causes of these changes.

METHODS

The medical records of patients who underwent unilateral horizontal lateral rectus recession and medial rectus resection for exotropia by a single surgeon over a period of 14 years were reviewed retrospectively. Using vector analysis, refractive changes in operated eyes (cases) were compared to changes in the sound eyes (controls). The main outcome measures were differences in mean change of refractive parameters and the proportion of clinically significant changes.

RESULTS

A total of 31 subjects (median age, 13.6 years; interquartile range, 8.8-19.8 years) were included. A significantly higher magnitude of refractive changes was observed in the operated eyes (P = 0.001). In addition, the proportion of cases with clinically significant change in sphere or cylinder was significantly higher in the operated eyes compared to the sound eyes (48% vs 10% [OR = 2.31, P = 0.002] and 32% vs 10% [OR = 5.0, P = 0.039], resp.).

CONCLUSIONS

Horizontal strabismus surgery is associated with refractive changes that might be of clinical significance. Pediatric ophthalmologists should consider re-refraction 1 month postoperatively.

Refractive Changes Induced by Strabismus Corrective Surgery in Adults

Purpose. To investigate refractive changes after strabismus correction procedures among adults. Methods. Retrospective chart review of adult patients who had horizontal recti muscles surgery with preoperative and postoperative cycloplegic refraction measurements. The preoperative refraction was mathematically subtracted from the postoperative refraction, and the induced refractive changes were statistically analyzed. Vector analysis was used to examine the magnitude of the toric change. The proportion of clinically significant refractive change was evaluated as well. Results. Thirty-one eyes from 22 subjects met the criteria and were included in the final analysis. A significant postoperative refractive change of the spherical equivalent towards myopia and a change of the astigmatism in the with-the-rule direction were observed. In a subset of 9 cases a third cycloplegic refraction measurement demonstrated stable refraction compared to the 1-month postoperative measurement. In 10 cases of single eye surgery, significant refractive changes were observed only in the operated side when compared to the sound eye. The induced surgical refractive change was of clinical significance (≥0.5 D) in 11 eyes of 9 patients (40.9% of patients). Conclusions. Refractive changes are a significant side effect of horizontal strabismus corrective surgery among adults. Therefore, patients should be informed about it prior to surgery and should be rerefracted in the postoperative period.

Comparison of Astigmatism Induced by Combined Inferior Oblique Anterior Transposition Procedure and Lateral Rectus Recession Alone

PURPOSE

The purpose of this study is to compare the magnitude and axis of astigmatism induced by a combined inferior oblique (IO) anterior transposition procedure with lateral rectus (LR) recession versus LR recession alone.

METHODS

Forty-six patients were retrospectively analyzed. The subjects were divided into two groups: those having concurrent inferior oblique muscle overaction (IOOA) and intermittent exotropia (group 1, 20 patients) and those having only intermittent exotropia as a control (group 2, 26 patients). Group 1 underwent combined anterior transposition of IO with LR recession and group 2 underwent LR recession alone. Induced astigmatism was defined as the difference between preoperative and postoperative astigmatism using double-angle vector analysis. Cylinder power, axis of induced astigmatism, and spherical equivalent were analyzed at 1 week, 1 month, and 3 months after surgery.

RESULTS

Larger changes in the axis of induced astigmatism were observed in group 1, with 4.5° incyclotorsion, than in group 2 at 1 week after surgery (axis, 84.5° vs. 91°; p < 0.001). However, there was no statistically significant inter-group difference thereafter. Relaxation and rapid regression in the incyclotorsion of induced astigmatism were observed over-time. Spherical equivalent significantly decreased postoperatively at 1 month in both groups, indicating a myopic shift (p = 0.011 for group 1 and p = 0.019 for group 2) but did not show significant differences at 3 months after surgery (p = 0.107 for group 1 and p = 0.760 for group 2).

CONCLUSIONS

Combined IO anterior transposition procedures caused an increased change in the axis of induced astigmatism, including temporary incyclotorsion, during the first week after surgery. However, this significant difference was not maintained thereafter. Thus, combined IO surgery with LR recession does not seem to produce a sustained astigmatic change, which can be a potential risk factor of postoperative amblyopia or diplopia compared with LR recession alone.

Effect of Orbital Decompression on Corneal Topography in Patients with Thyroid Ophthalmopathy

Objective

To evaluate changes in corneal astigmatism in patients undergoing orbital decompression surgery.

Methods

This retrospective, non randomized comparative study involved 42 eyes from 21 patients with thyroid ophthalmopathy who underwent orbital decompression surgery between September 2011 and September 2014. The 42 eyes were divided into three groups: control (9 eyes), two-wall decompression (25 eyes), and three-wall decompression (8 eyes). The control group was defined as the contralateral eyes of nine patients who underwent orbital decompression surgery in only one eye. Corneal topography (Orbscan II), Hertel exophthalmometry, and intraocular pressure were measured at 1 month before and 3 months after surgery. Corneal topographic parameters analyzed were total astigmatism (TA), steepest axis (SA), central corneal thickness (CCT), and anterior chamber depth (ACD).

Results

Exophthalmometry values and intraocular pressure decreased significantly after the decompression surgery. The change (absolute value (|x|) of the difference) in astigmatism at the 3 mm zone was significantly different between the decompression group and the controls (p = 0.025). There was also a significant change in the steepest axis at the 3 mm zone between the decompression group and the controls (p = 0.033). An analysis of relevant changes in astigmatism showed that there was a dominant tendency for incyclotorsion of the steepest axis in eyes that underwent decompression surgery. Using Astig PLOT, the mean surgically induced astigmatism (SIA) was 0.21±0.88 D with an axis of 46±22°, suggesting that decompression surgery did change the corneal shape and induced incyclotorsion of the steepest axis.

Conclusions

There was a significant change in corneal astigmatism after orbital decompression surgery and this change was sufficient to affect the optical function of the cornea. Surgeons and patients should be aware of these changes.

Is Inferior Oblique Overaction Associated With Astigmatism?

PURPOSE

To study the relationship between inferior oblique muscle overaction and astigmatism, and to explore any change in astigmatism after surgery.

METHODS

This was a retrospective chart review of patients undergoing strabismus surgery. Demographic data collected included age, diagnosis, preoperative refraction, presence of inferior oblique overaction, surgery performed, and postoperative refraction. Patients were divided into three groups: those having only horizontal strabismus without inferior oblique overaction (no inferior oblique group) as a control group, those having bilateral inferior oblique overaction (bilateral inferior oblique group), and those having unilateral inferior oblique overaction (unilateral inferior oblique group). Right eyes of the bilateral inferior oblique and no inferior oblique groups were chosen for analysis, whereas the eye with inferior oblique overaction was included in the unilateral cases. Refractions were converted to power vector coordinates for comparison. Statistical analysis was performed to compare the power vectors among groups using the no inferior oblique group as controls and to explore any postoperative change in astigmatism.

RESULTS

One hundred eighteen patients undergoing strabismus surgery were included (60 males and 58 females; mean age: 11.31 ± 10.59 years). Patients were divided into three groups: those having only horizontal strabismus without inferior oblique overaction (no inferior oblique group; 60 patients) as controls, those having bilateral inferior oblique overaction (bilateral inferior oblique group; 41 patients), and those having unilateral inferior oblique overaction (unilateral inferior oblique group; 17 patients). Preoperatively, there were no differences in astigmatism when comparing eyes with and without inferior oblique overaction. Postoperatively, both the no inferior oblique group and the bilateral inferior oblique group equally showed an increase in with-the-rule cylinder power (P = .02 and .01, respectively).

CONCLUSIONS

Inferior oblique muscle overaction did not result in an increased prevalence of astigmatism along the axis of the overacting muscle.

Surgically induced astigmatism following medial rectus recession: short-term and long-term outcomes

PURPOSE

The current study aimed to investigate short- and long-term postoperative ocular refractive effects of medial rectus recession on the involved eye and to describe the detectable effects in detail by the results of vector analysis.

METHODS

Data of patients in whom medial rectus recession was performed between 2010 and 2012 were retrospectively evaluated. The study included 52 eyes of 32 patients. Patients with a history of previous ocular surgery, congenital or progressive corneal disease, familial or acquired posterior segment disease, glaucoma, a history of ocular trauma, or any neurological or systemic disease were excluded. Best-corrected and uncorrected visual acuities and refraction examination findings of the patients were recorded before the surgery and at the postoperative first month and first year. A vector analysis program was used to analyze surgically induced astigmatism.

RESULTS

Significant myopic shift and astigmatic change were determined in the spherical equivalent refraction in the early postoperative period (first month); however, these changes disappeared in the long term (at the postoperative first year). A positive correlation was not observed between the amount of surgical recession and the results of ophthalmic examination at the postoperative first month and first year.

CONCLUSIONS

Only postoperative first month spherical equivalent showed a positive correlation with the amount of surgical recession; however, this correlation disappeared at the postoperative first year.

Changes in refractive error and anterior segment parameters after isolated lateral rectus muscle recession

PURPOSE

To evaluate the short-term effect of isolated lateral rectus muscle recession surgery on refractive error, corneal measurements, and anterior chamber depth and volume.

METHODS

Consecutive patients who underwent isolated lateral rectus muscle recession from July 2008 to March 2009 were prospectively studied. Refractive error; corneal power, thickness, and volume; and anterior chamber depth and volume were measured (Pentacam) before and at 1 week and 1 month after surgery. Patients who could not maintain reliable fixation and those with sensory strabismus or a history of eye surgery were excluded. Pre- and postoperative measurements were compared by analysis of variance.

RESULTS

A total of 24 eyes of 24 patients (average age, 8 years) were included. Bilateral lateral rectus muscle recession was performed in 19 patients; unilateral in 5. Overall, patients manifested statistically significant changes in spherical equivalent, horizontal and mean keratometry, corneal astigmatism, anterior chamber volume, and center and peripheral anterior chamber depth at 1 week after surgery (P < 0.05). Changes became progressively smaller during the first month after surgery, although significant changes in spherical equivalent persisted at 1 month.

CONCLUSIONS

Lateral rectus muscle recession resulted in short-term changes in refractive error in this cohort. The etiology of the refractive change is unknown but could be due to alterations in muscle tension that affect corneal remodeling, segmental interruption of the ciliary body circulation affecting the lens curvature, postoperative tissue edema, and/or other postsurgical factors. The decrease in change after 1 month may be due to the effects of compensation by other quadrants of the eye or resolution of the surgical induced tissue damage. Longer follow-up is necessary to ascertain clinical significance.

Astigmatic changes after horizontal rectus muscle surgery in intermittent exotropia

PURPOSE

To evaluate the changes of refractive astigmatism after horizontal rectus muscle surgery in intermittent exotropic children.

METHODS

Sixty-nine exotropic patients were retrospectively reviewed. Of those, 35 patients received unilateral lateral rectus recession (BLR group, 35 eyes) and 34 patients received unilateral lateral rectus recession and medial rectus resection (R&R group, 34 eyes). Non-cycloplegic refractions were measured until 6 months postoperatively. Spherical equivalent (SE), J0 and J45 using power vectors were calculated to determine and compare the changes of refractive astigmatism and axis in both groups.

RESULTS

SE significantly decreased after surgery for the first week and did not changed thereafter in both groups (p = 0.000 and p = 0.018, respectively). In BLR group, J0 showed significant changes at the first week and 1 month after surgery (p = 0.005 and p = 0.016, respectively), but in R&R group, J0 changed significantly between 1 week and 3 months postoperatively (p = 0.023 and p = 0.016, respectively). J45 did not change significantly as time passed in both groups (all p > 0.05). There was no statistically significant difference in the magnitude of changes in SE, J0 and J45 between the two groups after the 6-month follow-up (p = 0.500, p = 0.244 and p = 0.202, respectively).

CONCLUSIONS

Horizontal rectus muscle surgery in intermittent exotropic children tends to induce a statistically significant change in astigmatism in the with-the-rule direction and myopic shift in SE. This astigmatism change seems to occur within the first 3 months after surgery. Thus, astigmatism induced by surgery should be checked and corrected at least 3 months after horizontal strabismus surgery.

Comparison of preoperative and postoperative anterior segment measurements with Pentacam® in strabismus surgery

PURPOSE

This study was intended to evaluate the effect of horizontal muscle surgery on anterior segment measurements in patients with strabismus.

METHODS

Forty-two eyes of 28 patients with exotropia undergoing recession or recession combined with resection procedure were included. Consecutive cases were imaged using a Pentacam (Oculus, Inc., Berlin, Germany) immediately prior to surgery and 1 and 3 months after surgery. The refractive power of the anterior surface of the cornea on the horizontal and vertical axis, the thinnest corneal thickness, anterior chamber depth, anterior chamber volume, and cornea volume were analyzed. The clinical characteristics of patients, visual acuity, astigmatism, and size of the deviations before and after surgery were reviewed.

RESULTS

Muscle recession and recession plus resection surgery were performed in 28 and 14 eyes, respectively. Overall, no significant changes were noted when comparing preoperative and postoperative data. Patients were divided into two groups, recession or recession plus resection, and only anterior chamber depth was found to be significantly reduced in the recession group 1 month postoperatively. Three months postoperatively, the reduced anterior chamber depth in the recession group returned to the preoperative value.

CONCLUSION

In this series, the recession procedure in patients with strabismus induced an anterior chamber depth change during the early postoperative period. However, the anterior chamber depth returned to its preoperative state by 3 months after surgery. These findings indicate that extraocular muscle surgery could induce reversible changes to the anterior segment of the eye.

Transient increase of higher-order aberrations after lateral rectus recession in children

The changes of higher-order aberrations (HOAs) after bilateral lateral rectus muscle recession were evaluated. Forty eyes of 20 children were enrolled and their wavefront information was assessed until postoperative 3 months. Even though the root mean square (RMS) of total aberration was not changed, the RMS of HOA was transiently increased at postoperative 1 week and returned to baseline level after 1 month. Among individual Zernike coefficient, secondary astigmatism, quadrafoil, secondary coma, secondary trefoil, and pentafoil showed similar tendency with the RMS of HOA. However, coma, trefoil, and spherical aberration were not changed. Regarding recession amount, it did not correlate with any Zernike coefficient. In summary, our data imply that the HOAs are transiently increased after lateral rectus recession surgery. These results are in collusion with previous reports that strabismus surgery induced transient corneal astigmatism.

Astigmatism in Children With Epiblepharon

PURPOSE

To study the relationship between astigmatism and epiblepharon in Taiwanese children that need surgical correction.

METHODS

In a retrospective case-control study, a total of 254 eyes in 134 children surgically treated for lower-lid epiblepharon were studied. A further 205 eyes in 104 children 4-7 years of age were included as controls. Data on age, sex, severity of preoperative corneal erosion, best-corrected visual acuity, and preoperative and postoperative refractive errors were recorded. The data of astigmatism were decomposed into P90 (at 90 degrees) and its oblique meridian Pobl. Nonparametric tests were used to compare the severity of astigmatism.

RESULTS

No significant difference between age group (<4, 4-7, >7 years) in P90 was shown in children with epiblepharon. Pobl was trivial in each group of epiblepharon. Children with epiblepharon 4-7 years of age had significantly (P < 0.001) greater P90 than controls (1.12 vs. 0.47 D). P90 and Pobl were not significantly changed postoperatively. In the same individual, the eye with the more severely affected cornea had greater astigmatism (P = 0.002), even after the corneal erosion healed.

CONCLUSIONS

Children with epiblepharon who needed surgery had greater with-the-rule astigmatism than controls. More severe corneal erosion was associated with higher astigmatism. Surgical correction of skinfold and promotion of reepithelialization did not attenuate astigmatism significantly.

Refractive effect of the horizontal rectus muscle recession

PURPOSE

To determine refractive and corneal topographic changes after horizontal rectus muscles recession.

METHODS

In a noncomparative interventional case series, 49 eyes of 27 patients were evaluated in two groups: (1) exotropic patients (24 eyes) who underwent lateral rectus muscle(s) recession, and (2) esotropic patients (25 eyes) who underwent medial rectus muscle(s) recession. Full ophthalmic examination including cycloplegic automated refraction was carried out before, 1 and 3 months after surgery. Corneal topography was performed preoperatively and repeated at 3 months postoperatively.

RESULTS

In eyes underwent medial rectus recession, there were statistically significant myopic shifts in spherical equivalent at month 1 (from +2.09+/-1.82 to +1.88+/-1.83 diopters, P=0.03) and in astigmatic power at both month 1 (from -0.85+/-0.67 to -1.15+/-0.65 diopter, P=0.04) and month 3 (from -0.85+/-0.67 to -1.16+/-0.65 diopter, P=0.01). Myopic shifts were also noted following lateral rectus recession; however, there were not statistically meaningful. Significant astigmatic axis shift, which was toward with the rule astigmatism, was detected only after lateral rectus recession at both month 1 (P=0.02) and month 3 (P=0.02). Corneal power measured by topography was also demonstrated a statistically significant reduction (less than 0.3 diopter) after recession of either medial (P<0.001) or lateral (P<0.001) rectus muscle.

CONCLUSIONS

In spite of being statistically significant in some parts, the amounts of refractive and corneal topographic changes were not clinically remarkable. Therefore, it does not seem necessary to perform cycloplegic refraction early after horizontal rectus muscle recession; however, a precise refraction in all cases of strabismus should not be deferred later than 3 months.

A review of astigmatism and its possible genesis

Astigmatism is a refractive condition encountered commonly in clinical practice. This review presents an overview of research that has been carried out examining various aspects of this refractive error. We examine the components of astigmatism and the research into the prevalence and natural course of astigmatic refractive errors throughout life. The prevalence of astigmatism in various ethnic groups and diseases and syndromes is also discussed. We highlight the extensive investigations that have been conducted into the possible aetiology of astigmatism, however, no single model or theory of the development of astigmatism has been proven conclusively. Theories of the development of astigmatism based on genetics, extraocular muscle tension, visual feedback and eyelid pressure are considered. Observations and evidence from the literature supporting and contradicting these hypotheses are presented. Recent advances in technology such as wavefront sensors and videokeratoscopes have led to an increased understanding of ocular astigmatism and with continued improvements in technology, our knowledge of astigmatism and its genesis should continue to grow.

Combined strabismus and lens surgery

BACKGROUND

Simultaneous eye muscle and lens surgery in patients with strabismus and lens abnormalities offers the advantage of avoiding staged surgery.

METHODS

Thirty-three combined strabismus and lens surgeries were performed on 30 patients who ranged in age from 22 months to 91 years. Fifteen of the strabismus procedures were performed for esotropia, 12 for exotropia, 4 for vertical deviations, and 2 for combined vertical-horizontal deviations. Surgical amounts often were reduced to lessen the risk of overcorrection, to minimize anesthetic requirements (when using topical rather than general anesthesia), or to avoiding additional surgery on the contralateral or ipsilateral eye. The intraocular surgeries included cataract extraction without or with posterior chamber intraocular lens, secondary intraocular lens implantation, and YAG laser posterior capsulotomy. In 28 cases, muscle and intraocular surgery was performed on the same eye, and in 5 cases the strabismus surgery was performed on the eye opposite the intraocular surgery.

RESULTS

The average length of postoperative follow-up was 23.2 months (range, 1-94 months). Surgical, anesthetic, and postoperative complications, other than unsatisfactory ocular alignment, were limited to one retinal detachment in a patient with persistent fetal vasculature. Strabismic undercorrections (>12(Delta) of horizontal deviation or >5(Delta) of vertical deviation) occurred in 11 cases (37%). There were no overcorrections. A poor visual response (<20/50) to the intraocular surgery was encountered in 6 patients, all as the result of amblyopia or preexisting vitreoretinal pathology.

CONCLUSIONS

Simultaneous extraocular muscle and lens surgery is an option for patients with strabismus and lens abnormalities. Standard strabismus surgical amounts are recommended.

Symptomatic corneal topographic change induced by reading in downgaze

OBJECTIVE

To elucidate the cause of monocular blur or diplopia after reading in downgaze.

METHODS

Corneal topography was obtained before and after a 15-to 30-minute reading effort in downgaze in three symptomatic patients and in nine asymptomatic control subjects.

RESULTS

Changes in corneal topographic color maps, corneal uniformity index, and predicted corneal acuity were found in the symptomatic patients but not in the control subjects before and after reading.

CONCLUSION

Changes in corneal topography can occur after prolonged reading in downgaze and may produce symptoms of blur or monocular diplopia.