Clinical Characteristics And Accommodative Function Of Convergence Insufficiency Intermittent Exotropia

Objective:To investigate the clinical features of convergence insufficiency intermittent exotropia（CI-IXT）and the risk factors of stereopsis impairment.And to explore the accommodative functions of CI-IXT and its relationship with stereopsis,as well as the effect of surgery on accommodation.Methods:Clinical features of CI-IXT and risk factors affecting stereopsis were investigate in the first part.The clinical data of CI-IXT and basic intermittent exotropia（B-IXT）in the medical record database of Xijing Hospital,Air Force Military Medical University from January 2018 to January 2022 were retrospectively analyzed.General information such as gender,surgery age,onset age,as well as ophthalmic examination,including best corrected visual acuity（BCVA）,refraction,deviation,ocular muscle dysfunction,and stereopsis were collected.（1）To systematically summarize the clinical characteristics of CI-IXT by comparing the differences of demographic and clinical features between CI-IXT and common subtypes B-IXT.（2）According to the presence or absence of near or far stereopsis,they were divided into presence stereopsis group and absence stereopsis group.Univariate and multivariate logistic regression analyses were performed to screen factors affecting CI-IXT stereopsis.Factors to be analyzed include basic information and parameters related to strabismus.Potential risk factors identified by univariate logistic regression analysis were included and multivariate logistic regression models were constructed to identify independent risk factors affecting CI-IXT stereopsis.Accommodative functions of CI-IXT were analyzed in the second part.A prospective study was performed in which CI-IXT patients who underwent surgery at the Department of Ophthalmology,Xijing hospital,Air Force Military Medical University from June 2021to August 2022 were selected.Age-matched concurrent B-IXT and normal subjects were used as controls.General information,accommodative response,accommodative amplitude,accommodative facility,positive and negative relative accommodation（PRA/NRA）,accommodation convergence and accommodation ratio（AC/A）and near point-convergence（NPC）were tested.（1）Abnormal changes in CI-IXT were analyzed by comparing the differences in accommodative parameters among CI-IXT,B-IXT and normal controls.（2）CI-IXT were divided into absent stereopsis group and precent stereopsis group according to near stereoauity.The differences of accommodative parameters between the two groups were compared,and the relationship between stereopsis and abnormal accommodative function was analyzed.（3）To compared the accommodative parameters of CI-IXT before and last follow-up time after surgery,and explore the effect of surgery on accommodative function.Results:PartⅠ:Clinical characteristics of CI-IXT.In this study,the medical records of 615cases of CI-IXT and 222 cases of B-IXT were collected.The median surgery age for CI-IXT was 10 years（range:5-53 years）,much earlier than 17 years（range:3-49 years）for B-IXT（P<0.001）;although the median onset age for both subtypes was similar（P=0.457）,the median duration of misalignment for CI-IXT was 3 years（IQR:1,8 years）,shorter than 6 years（4,16 years）for B-IXT（P<0.001）.The median near exodeviation of CI-IXT was 65 prism diopter（PD）（50,85PD）,the distance exodeviation was 40 PD（30,60PD）,and the near-distance disparity（NDD）was 20 PD（10,30PD）.The median near exodeviation of B-IXT was 85 PD（40,90PD）,the distance exodeviation was 80 PD（40,90PD）,and the NDD was 5 PD（0,5PD）.The near exodeviation of CI-IXT was not significantly different from that of B-IXT（P=0.626）,while the distance exodeviation was significantly lower than that of B-IXT（P<0.001）.We observed CI-IXT combined with dissociated vertical deviation（DVD）in 17 patients（2.8%）,inferior oblique overaction（IOOA）in 291 patients（47.3%）,and superior oblique palsy（SOP）in 15 patients（2.4%）;B-IXT combined with DVD in 17 patients（7.7%）,IOOA in 133 patients（59.9%）,and SOP in 12 patients（5.4%）,so CI-IXT combined with ocular muscle dysfunction was less than B-IXT(P_DVD=0.002,P_IOOA=0.001,P_SOP=0.032).There were normal near stereopsis in283 cases（46.0%）,normal distance stereopsis in 92 cases（15.0%）,near suppression in193 cases（31.4%）,and distance suppression in 245 cases（39.8%）in CI-IXT;there were normal near stereopsis in 65 cases（29.3%）,normal distance stereopsis in 12 cases（5.4%）,near suppression in 98 cases（44.1%）,and distance suppression in 111 cases（50.0%）in B-IXT,so CI-IXT binocular function was superior to B-IXT(P_{near stereopsis}<0.001,P_distancestereopsis<0.001,Pnear suppression=0.001,Pdistance suppression=0.008).The surgery age between 6 to 12 years compared with less than 6 years（odds ratio[OR]=0.595,P=0.047;compared with≤6 years）was inversely associated with poor near stereopsis,whereas duration of misalignment more than 4 years,amblyopia,large exodeviation at distance and anisometropia>1.00D were positively associated with poor near stereopsis.The onset age older than 6 years compared with less than 3 years was associated with better distance stereopsis,whereas distance exodeviation larger than 30PD,and dominant eye BCVA worsen than 0.20 were positively associated with poor distance stereopsis.Part Ⅱ:Abnormal changes in CI-IXT accommodative function.A total of 75 CI-IXT patients,11 B-IXT patients and 20 normal controls were enrolled in this study.During binocular viewing,the different of CI-IXT and B-IXT accommodative responses was abnormal compared with the control group,mainly manifested in a significant increase in dominant eye accommodative lead and abnormal accommodative lag（P=0.009）,>0.00D accommodative lead in 22 patients（29.3%）in the CI-IXT group,3 patients（27.3%）in the B-IXT group,and 2 patients（10.0%）in the control group,>1.00D accommodative lag in14 patients（18.7%）in the CI-IXT group,5 patients（45.5%）in the B-IXT group,0 patients（0.0%）in the control group,while 90.0%patients was 0.00～1.00D accommodative lag in the control group;abnormal accommodative lag was significantly increased in the non-dominant eye（P=0.031）,and>1.00D accommodative lag was significantly increased in 23 patients（30.7%）in the CI-IXT group,5 patients（45.5%）in the B-IXT group,and 0patients（0.0%）in the control group.The median PRA was significantly higher in both CI-IXT-3.69±1.80 D and B-IXT-4.40±2.05 D groups than in the control group-2.64±0.97 D（P=0.047,P=0.021）.The median AC/A was significantly lower in the CI-IXT group than in the B-IXT group and the control group（P=0.003,P<0.001）,2.00△/D（1.67,3.00△/D）in the CI-IXT group,3.33△/D（3.00,4.00△/D）in the B-IXT group,and 4.00△/D（3.33,5.00△/D）in the control group.NPC was significantly higher in CI-IXT group than in control group（P<0.001）,6.80cm（4.00,7.00cm）in CI-IXT group,3.10cm（2.13,4.15cm）in control group.In CI-IXT,when binocular viewing,dominant eye accommodative response was higher than non-dominant eye（P<0.001）;when monocular viewing,non-dominant eye accommodative amplitude and accommodative facility was lower than dominant eye（P=0.020,P=0.046）,that is,CI-IXT binocular accommodative function showed asymmetric changes,while the control had balanced and accurate accommodative function.The relationship between asymmetry accommodative function and stereopsis was further analyzed.We collected absent stereopsis group（n=17）,present stereopsis group（n=58）and control group（n=20）.During binocular viewing,the difference between the dominant eye and the non-dominant eye median accommodation response was-1.00D（-1.50,-0.38D）in the absent stereopsis group,-0.13D（-0.75,0.25D）in the present stereopsis group,and 0.00D（0.00,0.19D）in the control group;the disparity between the two eyes accommodative response was significantly higher in the absent stereopsis group than in the present stereopsis group and the control group（P=0.001,P<0.001）,so there are relationship between asymmetry accommodation and stereopsis.Effect of surgery on accommodative function.The data of accommodative parameters of 17 patients with CI-IXT who were reexamined at last follow-up time 37.13±10.25 days after surgery were collected.The mean disparity of accommodative response between dominant eye and non-dominant eye was-0.34±0.66 D preoperatively and-0.07±0.28D postoperatively when binocular viewing.The disparity after surgery was smaller than that preoperatively,but the difference was not statistically significant（P=0.073）.The mean accommodative amplitude was 7.44±1.41 D preoperatively and10.90±2.43 D postoperatively when binocular viewing,and the accommodative amplitude postoperatively was significantly higher than that preoperatively（P<0.001）.The dominant eye mean accommodative amplitude was 9.59±2.23 D preoperatively and 11.18±2.54 D postoperatively when monocular viewing,and the accommodative amplitude postoperatively was significantly higher than that preoperatively（P=0.045）.The mean accommodative facility was 10.67±2.12 cpm preoperatively and 12.35±2.33 cpm postoperatively when binocular viewing,and the accommodative facility increased postoperatively compared with preoperatively（P=0.008）.When monocular viewing,the dominant and non-dominant eye mean accommodative facility was 10.80±2.75 cpm and10.23±2.62 cpm preoperatively,as well as 12.31±2.39 cpm and 12.20±2.48 cpm postoperatively,respectively,and the accommodative facility of both eyes increased postoperatively compared with that preoperatively（P=0.043,P=0.004）.Conclusion:CI-IXT has earlier surgery age,shorter duration of misalignment,less ocular muscle dysfunction ratio and superior binocular function than B-IXT.Risk factors affecting CI-IXT stereopsis included onset age,duration of misalignment,BCVA,distant exodeviation,and anisometropia.In addition,there were abnormal changes in the accommodative function of CI-IXT:increased accommodative lag in non-dominant eye compared with the dominant eye,decreased AC/A,distant NPC and asymmetric accommodative function.This asymmetry change was associated with absent stereopsis.Ocular muscle surgery has positive influence for the accommodative function of CI-IXT.The results of this study help ophthalmologists deepen their comprehensive understanding of CI-IXT and provide a theoretical basis for the formulation of clinical management strategies during diagnosis,treatment,and monitoring,thereby promoting the accuracy of CI-IXT diagnosis and treatment.