Intermittent exotropia is the most common type of strabismus in Asia. There are many academic controversies on the hot topics, such as surgical timing, initially postoperative target for good outcomes in long term, indications for nonsurgical treatments. The authors reviewed the recent progress of studies on intermittent exotropia based on the clinical practice to provide some ideas and guidance to the domestic ophthalmologists.

Objective: To observe the pulley insertion location and extraocular rectus muscle changes in intermittent exotropia using the magnetic resonance imaging (MRI) technique. Methods: This was a case series study. Data were collected from January 2017 to June 2017 at Tianjin Eye Hospital. Thirty-two patients who were diagnosed with intermittent exotropia included 17 males and 15 females, whose average age was 15.4 ± 1.8 years. Thirty normal volunteers whose average age was 16.1 ± 1.6 years were used for comparison. MRI coronal scans were performed on the pulley insertion locations of the extraocular rectus muscles. Linear regression and correlation coefficients were calculated, as well as the maximum cross-sectional area and volume changes of the extraocular rectus muscles in the primary gaze, and were analyzed by an independent samples t test.results: The difference in pulley insertion locations of the extraocular rectus muscles between intermittent exotropia patients and normal volunteers was not significant. However, the maximum cross-sectional area changes of the medial rectus muscle in intermittent exotropia was smaller compared to the normal volunteers and the volume changes of the medial rectus muscles were significantly weaker (t =10.47,P=0.006). The maximum cross-sectional area of the lateral rectus muscles was larger in intermittent exotropia patients than in the normal volunteers but the difference was not significant. The ratio of the lateral rectus/medial rectus muscle volume was significantly different (t=7.33, P=0.007), it was larger in intermittent exotropia patients (1.6 ± 0.4) than in normal volunteers (1.1 ± 0.1). conclusions: In patients with intermittent exotropia, MRI scans show that the maximum cross-sectional area of the medial rectus muscle decreases and the volume is smaller, while the ratio of the volume of the lateral rectus/medial rectus muscle is much larger. This indicates that the mechanism for intermittent exotropia is related to a change in the horizontal rectus muscle, not the pulley insertion location.

Objective: To evaluate the accommodative facility and accommodative response in patients with intermittent exotropia. Methods: Thirty-five patients with basic intermittent exotropia and 24 normal controls were recruited for a case control study at Eye Hospital, Wenzhou Medical University from October 2016 to January 2017. Binocular and monocular accommodative facility were tested using a ± 2.00 diopter (D) flip. Accommodative responses under binocular and monocular viewing conditions at 40 cm were tested by an open-field autorefractor WAM-5500. Data were analyzed using t-tests. results: The binocular accommodative facility of intermittent exotropia was 8.8 ± 4.1 cycles per minute (cpm), which was significantly lower than the normal control, 10.9 ± 3.1 cpm (t=-2.165, P=0.035). The fixating eye of intermittent exotropia had higher monocular accommodative facility than the non-fixating eye (t=4.657,P<0.001). Under binocular viewing conditions, the fixating eye of the intermittent exotropia had a higher accommodative response than the fixating eye of the normal control (t=-2.163, P=0.035). The binocular
accommodative response was also higher than the accommodative response under monocular viewing conditions (t=3.801, P=0.001). conclusions: Patients with intermittent exotropia have low binocular accommodative facility. They also have asymmetric monocular accommodative facility and asymmetric accommodative responses between the fixating eye and the deviating eye. Patients with intermittent exotropia have a higher accommodative response under binocular viewing conditions than under monocular viewing conditions.

Objective: To observe the effect of perceptual learning in reconstructing stereopsis of postoperative comitant exotropia. Methods: In this prospective study, 23 postoperative exotropic patients who underwent surgery from August 2009 to August 2011 at the First Affiliated Hospital of Anhui Medical University were recruited. By three months after surgery, all patients were aligned but did not achieve normal stereopsis when examined by the Titmus stereo test. Patients were trained by a perceptual learning method based on disparity discrimination. Disparity discriminating accuracy and stereoacuity were measured before and after training. The data were analyzed using paired t-test. results: Two patients were excluded due to poor fusion. The average training time was 6.9 ± 3.8 days. After training, stereoacuity was significantly improved in all 21 patients (t=8.228, P<0.001). The disparity discriminating accuracy test showed that under disparities of 320″, 440″, and 580″, the accuracies were improved after training (t=-3.102, P=0.01;t=-2.360, P=0.02; t=-2.177, P=0.03 respectively). conclusions: Perceptual learning can be used in reconstructing stereopsis for postoperative exotropic patients, and the effect can be maintained. However,the exact mechanism by which the reconstruction of stereopsis occurs need further research.

Objective: To investigate the clinical characteristics and surgical outcomes of intermittent exotropia (IXT) with lateral incomitance (LI). Methods: This was a retrospective study. Thirty-two patients with IXT and LI were recruited from 381 patients from March 2016 to March 2017. All were evaluated for horizontal
deviations in the primary position, left side and right side with the prism and alternative cover test by the same doctor. LI+ was defined as a reduction in deviation at the side gaze of ≥10 △ compared to the primary position. Thirty-two patients were divided into group A (LI < 20 △ ) and group B (LI≥20 △ ). The deviation,IXT type, laterality and postoperative LI change were compared and analyzed between the two groups.Patients were followed up for 3 to 6 months. Two independent sample t test and Fisher accurate test were used for statistical analysis. results: Of 381 patients, 32(8.4%) had LI before surgery. Twenty-nine patients (91%) had basic type IXT, 3(9%) had convergence insufficiency type IXT and none had pseudo- or true divergence excess. 24(75%) had unilateral LI and 8(25%) had bilateral LI. The relative values of LI, which were equal to (absolute amounts of LI / deviations at distance in the primary position)×100%, were less than 40% in 24(75%) and ≥40% in 8(25%) patients, but postoperative LI were presented in 5 patients. There were no significant differences in compositions of the IXT type, laterality, relative value of preoperative LI or postoperative LI between the two groups. The average horizontal deviations in the primary position at distance and near in group B (-55.0 △ ± 7.6 △ , -60.0 △ ± 8.9 △ , respectively) were greater than the deviations in group A (-38.8 △ ± 12.4 △ , -44.8 △ ± 12.6 △ , respectively) (t=-3.49, -3.16, P < 0.05). However, there was no difference in the relative value of LI between the two groups (29.7% ± 10.4%, 35.0% ± 7.6%,respectively. After surgeries, the horizontal deviation in the primary position ranged +2 △ to -8 △ in all patients. conclusions: The basic type and unilateral LI are common in IXT with LI. The absolute amount
of LI maybe higher in IXT with a greater deviation. We consider LI defined by the absolute amounts may be more reliable. Consideration of the side effects of LI on surgery, an optimal surgical plan could make LI negative and avoid overcorrection in the primary position.

Objective: To compare the surgical efficiency of unilateral recession-resection and slanted medial rectus (MR) resection for convergence insufficient exotropia.Methods: In this prospective study, 36 patients with exotropia of convergence insufficiency treated in the ophthalmic center of the First Affiliated Hospital of
Zhengzhou University from September 2016 to February 2017. Patients were divided into three groups according to different surgical procedures including unilateral recession-resection (Group A, 16 cases),unilateral slanted MR resection (Group B, 9 cases), and bilateral slanted MR resection (Group C, 11 cases).In Group A, the amount of MR resection was based on the near deviation, and the amount of lateral rectus (LR) recession was based on the distant deviation. In Groups B and C, the upper edge of the MR was resected according to the distant exodeviation, and the lower edge of the MR was resected according to the near exodeviation. Successful outcome was defined as a postoperative residual deviation at a distance of ±10 △ . The proportion of postoperative success, the postoperative deviations at near and distant field, and the difference between near and distant field among the three groups were compared. results: At the final follow-up examination, the proportion of success in Group A (14/16 cases) was significantly higher than in Group B (2/9 cases) and Group C (4/11 cases) (P < 0.05). The mean deviation at near and distant in Group A was significantly lower than in Groups B and C (P < 0.05). There were no significant differences in the near and distant deviation among the three groups. conclusions: Unilateral recession-resection in which the MR resection is made according to the near deviation and the LR recession according to the distant deviation can successfully treat exotropia of convergence insufficiency better than the slanted MR resection.

Objective: To investigate the long-term clinical effects and postoperative changes in children with intermittent exotropia. Methods: In this retrospective case series study, 139 children with intermittent exotropia and who underwent strabismus surgery were followed for more than 12 months. Distant and near squint angles as well as binocular visual function parameters were collected preoperatively, at 1 week and 1 month postoperatively, and at the last follow-up. Independent sample t-tests were used to compare the distant and near squint angles between the pre- and postoperative periods. Chi-square tests were used to analyze distant and near sensory fusion and stereopsis. results: The mean age was 7.4 ± 2.6 years (range 4-14 years), and the follow-up time was 21.0 ± 10.5 months (range 12-51 months).The preoperative distant and near deviation were -33.9 △ ± 10.9 △ (range -20 △ -   -75 △ ) and -38.2 △ ± 10.2 △ (range-20 △ -   -85 △ ), respectively. At the final follow-up examination, the mean postoperative distant and near squint angles were -6.4 △ ± 8.0 △ (+16 △ -   -35 △ ) and -7.7 △ ± 9.6 △ (+ 20 △ -   -40 △ ) respectively. Among the patients, 103 cases (74.1%) were orthophoric, 35 cases (25.2%) had recurrent exotropia, and 1 case (0.7%) showed overcorrected strabismus. Bilateral visual acuity was significantly improved at the final follow-up examination. The distant and near perceptual fusion were significantly improved ( χ 2 =26.88,26.24, P < 0.001), as was the distant and near stereopsis ( χ 2 =64.38, P < 0.001; χ 2 =14.63, P=0.002). The 35 patients who relapsed at the last follow up had significantly improved perceptual fusion function ( χ 2 =14.58, P=0.002) and better distant and near stereopsis acuity, although the changes were not
statistically significant. conclusions: Approximately 75% of the children with intermittent exotropia maintained long-term orthophoria after surgery, and their binocular vision was significantly improved.Even in children with postoperative recurrence, binocular visual function was better than before surgery.

Objective: To evaluate the efficacy and safety of phototherapeutic keratectomy (PTK) and corneal collagen cross-linking (CXL) combined therapy on primary keratoconus. Methods: In this prospective,self-controlled clinical study, 11 patients (11 eyes) underwent treatment with combined PTK and CXL.Uncorrected visual acuity (UCVA), best corrected visual acuity (BCVA), refractive error, topography,corneal thickness, and endothelial cell density were evaluated preoperatively and at 12 months postoperatively. Data were analyzed using paired t-tests. results: At 12 months postoperatively, UCVA,sphere, and spherical equivalent improved significantly (t=3.692, P=0.008; t=-1.397, P=0.039; t=-2.363,P=0.040 respectively). Maximum K-value (Kmax) and corneal thinnest thickness decreased significantly
(t=2.941, P=0.007; t=3.839; P=0.003). There were no significant changes in endothelial cell density (t=-1.615, P=0.172). conclusions: PTK and CXL combined therapy was effective and safe in the treatment of progressive primary keratoconus.

Objective: To compare one-year clinical outcomes between small incision lenticular extraction (SMILE) and off-flap epipolis laser in situ keratomileusis (Epi-LASIK) for myopia. Methods: In this retrospective case-control study, choosing from Nanjing General Hospital of PLA between March 2013 and August 2014, 103 eyes of 52 patients underwent SMILE, and 86 eyes of 43 patients underwent off-flap Epi-LASIK.Uncorrected visual acuity (UCVA), best corrected visual acuity (BCVA), residual astigmatism, and spherical equivalent (SE) were evaluated preoperatively, at 1 day, 1 week, at 1, 3, and 6 months, and at 1 year postoperatively. Contrast sensitivity (CS), modulation transfer function (MTF), and wavefront aberrations were evaluated at 1 year postoperatively. Data were analyzed using repeated measures analysis of variance, independent-samples t-tests, and Chi-square tests. results: At 1 day and 1 week after surgery,the UCVA for the SMILE group was significantly better than for the Epi-LASIK group (t=5.065, 5.994,respectively, P<0.001 for both); however for all other follow-up times, there were no significant differences
in the UCVA between the two groups. At 1 year postoperatively, there was no significant difference in the frequency of eyes SE within ±0.5 diopter (D) or within ±1.0 D between the two groups respectively.However, the frequency with which the SMILE group attained a cylindrical refractive error within ±0.5 D was clearly higher than for the Epi-LASIK group ( χ 2 =10.734, P=0.001). The CS with glare at low spatial frequency [3 and 6 cycles per degree (cpd)] in the SMILE group was significantly higher than for the Epi-LASIK group (t=4.106, 3.848, P<0.001). However, there were no significant differences in CS at other spatial frequencies, with or without glare between the two groups. Total order aberrations, lower-order aberrations,higher-order aberrations, spherical aberrations, coma, trefoil aberrations, and MTFs at all spatial frequencies with 4.0-mm pupils were not significantly different between the two groups. However with 6.0-mm pupils,higher-order aberrations and spherical aberrations of the SMILE group were significantly lower than inthe Epi-LASIK group (t=3.881, 6.843, P<0.001 each). There were no significant differences in the other aberrations between the two groups. The MTFs were significantly higher in the SMILE group than in the Epi-LASIK group with 6-mm pupils at low and high spatial frequency (5, 20, 25, 30 cpd) (t=3.272,P=0.001; t=2.926, P=0.004; t=3.280, P=0.001; t=3.975, P<0.001 respectively). There were no significant differences in the MTFs at residual spatial frequency between the two groups. conclusions: Both SMILE and off-flap Epi-LASIK are safe, efficient, stable, and predictable for the treatment of myopia. However,SMILE had better correction of astigmatic error, and with 6.0-mm pupils, SMILE had better visual quality than off-flap Epi-LASIK.

Objective: To investigate outcomes of myopic astigmatism correction after transepithelial photorefractive keratectomy (TransPRK) for myopic astigmatism using the Alpins method, and to explore factors affecting the correction of astigmatism. Methods: In this retrospective study, 99 patients (167 eyes with myopic astigmatism) during January 2014 to June 2016 in Joint Shantou International Eye Center were chosen and then divided into a low astigmatism group (-0.25-   -0.75 D) and a high astigmatism group (-1.00-   -4.75 D).Astigmatism status was evaluated based on astigmatism before treatment and 3 months after treatment based on Alpins vector analysis. Pre-op and post-op indexes were compared with a paired t-test, and the correlation of factors affecting the correction of astigmatism was analyzed by Pearson correlation.results: Before surgery, spherical power was -3.57 ± 1.22 D and astigmatism was -0.93 ± 0.62 D based on subjective refraction; and 3 months after surgery spherical power was +0.12 ± 0.25 D and astigmatism was -0.04 ± 0.23 D. Target-induced astigmatism (|TIA|) was 0.86 ± 0.58 D, surgery-induced astigmatism (|SIA|) was 0.87 ± 0.59 D, the difference vector (|DV|) was 0.10 ± 0.21 D, the magnitude of error (ME) was 0.01 ± 0.17 D, the angle of error (AE) was 1.49° ± 13.27° and the correction index (CI) was 0.98 ± 0.33.|SIA| and |TIA| were positively correlated (r=0.94, P < 0.001), |AE| and |DV| were positively correlated (r=0.83, P < 0.001) and ME and |SIA| were positively correlated (r=0.23, P < 0.001). The two groups had a similar |DV|, ME and CI. The low astigmatism group's |AE| was 5.78° ± 16.34°, and the high astigmatism group's |AE| was 1.82° ± 4.41° (t=2.02, P=0.04). After TransPRK, 37 eyes (22.0%) had astigmatism, and 60% of eyes had an axis change of more than 30°. We found that the preoperative cylinder axis moved counter-clockwise to the postoperative cylinder axis, which changed -2.30° ± 45.88°. conclusions:Postoperative astigmatism using TransPRK has a close relationship with the accuracy of astigmatism and
axis correction. In order to reduce postoperative astigmatism, it is necessary to improve the accuracy of the astigmatism and axial direction during the procedure.

Sports vision is the ability of people to adjust their movements appropriately when they observe changes in the performance environment. It is a new discipline in the field of vision, and it includes evaluating and improving visual expression, diagnosing visual problems, and providing necessary visual training. Visual training is a way of training the eyes and the brain, and the stimulation and training of the brain's visual neurocognitive system. At present, sports vision has attracted extensive attention in many sporting events.The visual abilities of the athletes are fundamentally increased by long-term training and competition practice. This article reviews the research on the current understanding of the role of vision training in sports.