the data were collected from the records of patients presenting to outpatient department for piol surgery for myopia .
the inclusion criteria for the icl implantation were preoperative best - corrected distance visual acuity ( bdva ) of 6/24 ( snellen equivalent ) or better , stable refraction for at least 1 year and a clear central cornea with myopia or myopic astigmatism .
the exclusion criteria included the age younger than 18 years , anterior chamber depth < 2.8 mm ( as measured on pentacam ) , endothelial cell density < 2000 cells / mm , white to white measurement < 10 mm ( as measured on orbscan ii ) , presence of cataract , glaucoma , unlasered thinning , breaks or retinal detachment , macular degeneration or retinopathy , a past history of any episode of ocular inflammation , patients with severe dry eyes , or those corneal opacity or irregularity .
staar visian icl ( walker avenue , california , usa ) was implanted using the prescribed protocol by the same surgeon .
pre- and post - operative visual acuity ( snellen equivalent converted to logarithm of the minimum angle of resolution ) , stereoacuity , refractive error ( spherical , cylindrical , and spherical equivalent ) , and degree of anisometropia ( algebraic difference of the spherical equivalent between the two eyes ) were analyzed .
visual acuity was recorded postoperatively at day 1 , day 8 , and 4 weeks .
stereoacuity was tested with best - corrected visual acuity ( bcva ) and was recorded at 4 weeks of follow - up .
distance randot stereotest ( stereo optical co. , inc . , chicago , il , usa ) was administered while wearing polarizing glasses by trained masked optometrists at 3 m for distance stereopsis ( range 40060 arcsec ) .
near stereoacuity was measured using the tno test ( lameris instrumenten b.v . , utrecht , the netherlands ) and was administered at 40 cm using red , green anaglyphic filters .
chicago , il ) . for the purpose of analysis in the absence of actual quantitative value of stereoacuity tests for gross and null stereopsis , categorization of stereopsis was done into three categories as fine stereopsis ( < 480 on tno and < 400 arcsec on distance randot stereotest ) , gross stereopsis ( > 500 arcsec on tno and 7002000 arcsec on distance randot ) , and null stereopsis ( nonmeasurable stereopsis on test ) . mcnemar 's test was applied for calculating differences in frequency between the paired nominal data of stereoacuity categories pre- and post - operatively .
wilcoxon signed rank test was used to calculate significance levels for the difference before and after surgery .
two sample paired t - test was applied to calculate the relationship among change in stereoacuity with change in visual acuity , spherical equivalent , and anisometropia .
all patients were operated bilaterally , except one who had unilateral myopia ( total of 95 eyes ) . the surgery and postsurgical course were uneventful in all eyes except in one eye , which showed raised intraocular pressure postoperatively , for that augmentation of yag iridotomy had to be performed .
the mean spherical error was 9.9  5.5 d ( range : 1 to  19 ) , and the mean cylindrical error was 1.11  1.7 d ( range : 6 to 0 d ) .
the average spherical equivalent of the population was  10.49  5.69 d ( range : 2.75 to  21 d ) .
pre- and post - operative demographic data of patients undergoing icl surgery there was a significant improvement in visual acuity ( both uncorrected distance visual acuity and bdva ) as compared to preoperative levels ( p < 0.001 ; wilcoxon signed rank test ) .
there was a significant improvement in stereoacuity for both near ( p = 0.001 ) and distance ( p = 0.0005 ) ( mcnemar 's test ) .
the difference ( two - sample paired t - test ) was not found to be statistically significant for change in near stereoacuity with change in ucva ( p = 0.3 ) , bcva ( p = 0.8 ) , spherical equivalent ( p = 0.8 ) , and anisometropia ( p = 0.5 ) .
the change in numbers of distance stereoacuity postoperatively did not allow a similar analysis for distance stereopsis .
1a and b. ( a ) graph showing change in near stereoacuity pre- and post - operatively .
( b ) graph showing change in distance stereoacuity pre- and post - operatively ( values in sec represents arc seconds ) the overall improvement in stereopsis was observed in 15/48 ( 31.25% ) and 13/48 ( 27.10% ) subjects for near and distance , respectively , with no significant difference between the two ( p = 0.82 ; fisher 's exact test ) [ table 2 ] .
improvement of stereoacuity among the stereoblind subjects was observed in 10/12 ( 83.33% ) and 13/36 ( 36.11% ) for near and distance , respectively [ fig .
there was a significantly greater improvement of near stereopsis in stereoblind subjects when compared with distance stereopsis ( p = 0.007 ; fisher 's exact test ) .
the odd 's ratio for near stereoacuity to improve in comparison to distance stereoacuity among the stereoblinds was 8.85 ( 95% confidence interval : 1.6846.70 ; p = 0.01 ) .
the change in stereoacuity pre- and post - operatively when divided into the categories nonrecordable , gross , and fine stereoacuity
in our series , the patients registered a significant improvement in both near and distance stereopsis postsurgery ( p < 0.001 ) . there are only anecdotal reports in literature describing the improvement in stereopsis following posterior chamber piols implantation . however , these studies were limited by reporting outcome for change in stereopsis in a small number of patients that were treated for varied refractive errors , at differing age and with different types of piol
. this may suggest that stereopsis is susceptible to recovery even later in adulthood if appropriate visual rehabilitation is offered .
enhanced stereoacuity postsurgery could be due to the greater retinal magnification of images ( 1147% ) at intraocular plane versus that at the spectacle plane , corresponding to an improved bdva of 0.4 and 1.8 lines .
other factors include the elimination of prismatic effect of spectacles , enhanced quality of vision in both eyes , correction of anisometropia , and infrequent use of glasses preoperatively
. the absence of any relationship of stereoacuity with anisometropia could be due to low degree of anisometropia in our patients ( median 0.87 d ) as anisometropia > 3d has the maximum potential to create blur and affect stereoacuity .
about 84% and 37% patients who were stereoblind for near and distance , respectively , improved following surgery .
the greater probability ( 8.84 ) of near stereoacuity to improve than distance may be because myopes have a good near vision despite having a poor distant vision .
further , stereoscopic disparity was measured dichoptically using two different principles , that is , polaroid vectograph - based and anaglyph - based principles for distance and near stereoacuity , respectively .
it could have resulted in slight differences in accuracy while comparing the distance and near stereo acuities obtained in this study .
moreover , patients with low , pre- and post - operative bcva could also have confounded the results in not producing improvement in stereoacuity .
nevertheless , this is the only study that sought the impact of icl implantation on the change in stereoacuity in myopia . to conclude , icl implantation aids in improving stereoacuity postoperatively .
it may be utilized as a therapeutic procedure for poor stereopsis preoperatively in certain sportspersons , e.g. in athletes , shooters , car racers . near stereopsis
 the study evaluated the impact of implantable collamer lens ( icl ) implantation on stereoacuity in myopes in a retrospective case series . 
 ninety - five eyes of 48 patients were recruited . 
 distance and near stereoacuity were measured using distance randot stereotest and tno test , respectively , before surgery and at 4 weeks postoperatively . 
 mean age of the patients was 23.67  3.7 years . 
 mean uncorrected distance visual acuity ( udva ) was 1.28  0.37 logarithm of the minimum angle of resolution ( logmar ) ( median : 1.3 ; range : 0.31.8 ) , and median best - corrected distance visual acuity ( bdva ) was 0.18 logmar ( range : 00.6 ) . 
 there was a significant improvement in both udva and bdva postsurgery ( p < 0.001 ; wilcoxon signed rank test ) . 
 the overall improvement in stereopsis was observed in 15/48 ( 31.25% ) and 13/48 ( 27.10% ) subjects for near and distance , respectively , with no significant difference between the two ( p = 0.82 ; fisher 's exact test ) . among stereoblind individuals , 
 the odd 's ratio for near stereoacuity to improve in comparison to distance stereoacuity was 8.85 ( 95% confidence interval : 1.6846.70 ; p = 0.01 ) . 
 icl implantation for refractive correction aided stereoacuity improvement in myopes more so for near . 