phakic intraocular lens ( piol ) provides internal compensation of the dysfunctional refractive condition of the phakic eye and reduces or eliminates the dependence on glasses or contact lens .
an implantable lens consisting of a biocompatible collagen copolymer ( visian implantable collamer lens [ icl ] ; staar surgical , nidau , switzerland ) was developed in 1993 as a posterior chamber piol and was called the implantable contact lens , as initially it was thought that it would come into contact with the anterior surface of the crystalline lens .
staar ( monrovia , ca , usa ) patented this material made of 60% poly - hydroxyethylmethacrylate 
hema , water ( 36% ) , benzophenone ( 3.8% ) , and 0.2% porcine collagen , and called it the collamer ( collagen - copolymer).1 , 2 icl is a posterior chamber phakic iol which is a soft , flexible gel - lens ushering an era of reversible refractive surgery .
icls are ciliary sulcus placed posterior chamber piols that can be implanted through a small ( 3.0  mm ) , self - sealing limbal / clear corneal incision .
in contrast with refractive lens exchange , icl implantation does not impair natural accommodation or increase the risk of retinal detachment above the background rate for untreated patients with high myopia , and have a good safety profile .
icl is a boon in achieving spectacle independence in patients who are unsuitable for laser refractive procedures like those with high myopia ( > 13diopter d ) , thin corneas , those with expected residual stromal bed thickness less than 300   , and severe dry eye . with its increasing acceptance and establishment of safety profile
, icl implantation has become an increasingly popular choice for the correction of moderate to high myopia.4 , 5 the convexo - concave design of the icl creates a vault between it and the anterior lens surface .
however , the previous v4b icl model is known to cause pupillary block , and so either a preoperative / intraoperative laser / surgical peripheral iridotomy / iridectomy ( pi ) is required . to overcome this additional step , the v4c model with a central hole ( 0.36  mm ) was developed in 2011 .
it has a central hole in addition to two additional holes outside the optic facilitating aqueous outflow and removal of ophthalmic viscosurgical device ( ovd ) during surgery .
however , complications of icl implantation such as cataract formation ( anterior subcapsular lens opacities - typical butterfly cataract ) , endothelial cell loss , pigment dispersion , intraocular pressure ( iop ) elevation , and secondary glaucoma have been reported , and these complications are expected to increase with time.4 , 5 studies have shown good acceptance profile of both the icl models.4 , 5 , 7 in view of the increasing prevalence of this surgical procedure , we conducted this study to evaluate the visual outcome , complication rate and safety indices of both the v4b and v4c icl models for the correction of high myopia in a tertiary eye care center in south india over a follow - up period of 9 months .
all patients undergoing icl implantation for the correction of high myopia ( manifest spherical equivalent  mse    6 d ) were included in the study .
the following were the inclusion criteria : ( a ) age between 21 and 45 years , ( b ) stable refraction within the past 1 year , ( c ) patients not suitable for corneal - based laser refractive procedures  those with abnormal corneal topography and keratoconus , predicted thin residual stromal bed thickness of less than 300   , high refractive errors of > 13 d , severe dry eye , ( d ) corneal diameter  >  11  mm , ( e ) internal anterior chamber depth  acd ( measured from endothelium )  >  2.9  mm .
bilateral implantation of the same icl model for the correction of bilateral moderate - high myopia was preferred in an individual patient .
a detail preoperative assessment was carried out including uncorrected distant visual acuity ( udva ) , corrected distant visual acuity ( cdva ) , iop measurement with non - contact tonometry 
nct ( nt-510 nidek technologies , japan ) and a gonioscopy to ensure wide open angles .
a detailed slit - lamp examination to rule out any ocular pathology was done . a detailed fundus examination to rule out any myopia - related or other fundus pathology was done , and prophylactic barrier laser , if required , was given . automated and manual keratometry values were recorded using topcon kr-8800 and ultrasound pachymetry using tomey pachymeter sp2000 .
corneal topography was performed using optikon 2000 keratron scout topographer ( optikon , italy ) and axial length and anterior chamber depth ( acd ) by sonomed pacscan 300a ( sonomed , inc .
the white - to - white ( wtw ) diameter was measured using a digital biometric ruler - digital calipers .
endothelial cell count ( ecc ) was measured using tomey em-3000 specular microscope ( tomey corporation , japan ) .
the icl power was calculated using the staar surgical customer service department formula that uses the acd , mean keratometry or simulated keratometry values , central corneal pachymetry , horizontal wtw distance , and refraction 12  mm from the corneal vertex .
the horizontal axis was marked with the patient sitting at the slit lamp prior to the surgery .
two dots were placed on the corneal - limbal area with a surgical marker indicating 0 and 180 meridians as reference for later toric icl ( ticl ) alignment .
pupillary dilatation was achieved with a combination eye - drop containing 1% tropicamide and 2.5% phenylephrine .
two 1  mm paracenteses were made using angled keratome or 15 side port knife at 12 and 6 o'clock positions .
hypromellose 2% ( viscomet pf , unimed technologies ) viscoelastic was injected into the anterior chamber taking care not to overfill the chamber .
the paracenteses were used to position the footplates under the iris using the special manipulating instruments like vukich 's manipulator .
it was ensured that all haptics were posterior to the iris . in case of v4b icl ,
the pupil was constricted with carbachol ( mio - chol , 0.01% preservative free , usa , marketed in india by appasamy associates ) , and a single pi at 1 the o'clock position was done with vitrector under viscoelastic cover . in case of v4c icl , this step was skipped . in case of ticl proper alignment was ensured . at the end of surgery , viscoelastic was cleared from the ac .
a standard postoperative regime consisting of topical prednisolone acetate 1% ( pred forte , allergan , usa ) 4 times a day for 5 days tapering over 2 weeks and topical gatifloxacin 0.3% ( zymaxid , allergan las , irvine , usa ) 4 times a day for 2 weeks was started .
timolol maleate eyedrops 0.5% ( timolet , sun pharmaceuticals , india ) was also started 2 times per day for 3 days .
postoperatively , the patient was examined at 4  h to check for proper icl positioning and vaulting on slit lamp , and iop was checked .
the patient was then followed on postoperative day 1 , 1 week , 1 month , 3 months , 6 months , and 9 months .
the main surgical outcomes were evaluated at 1 , 3 , 6 , and 9 months follow - up . at each of these visits , udva , cdva , mse , iop ,
icl vault was measured by anterior segment optical coherence tomography ( as - oct ) rtvue ( model - rt100 version 6.9 , fremont , usa ) .
patients were asked about subjective symptoms of glare and haloes at the end of follow - up period of 9 months .
the safety index was calculated by dividing the postoperative cdva ( in decimal ) at 9 months by the preoperative cdva ( in decimal ) .
the efficacy index was calculated by dividing the postoperative udva ( in decimal ) by the preoperative udva ( in decimal ) .
the data were analyzed using spss version 20 ( statistical package for social sciences ) with paired t - test for intragroup comparison and mann whitney u value test for intergroup comparisons .
pupillary dilatation was achieved with a combination eye - drop containing 1% tropicamide and 2.5% phenylephrine .
two 1  mm paracenteses were made using angled keratome or 15 side port knife at 12 and 6 o'clock positions .
hypromellose 2% ( viscomet pf , unimed technologies ) viscoelastic was injected into the anterior chamber taking care not to overfill the chamber .
the paracenteses were used to position the footplates under the iris using the special manipulating instruments like vukich 's manipulator .
it was ensured that all haptics were posterior to the iris . in case of v4b icl ,
the pupil was constricted with carbachol ( mio - chol , 0.01% preservative free , usa , marketed in india by appasamy associates ) , and a single pi at 1 the o'clock position was done with vitrector under viscoelastic cover . in case of v4c icl , this step was skipped . in case of ticl proper alignment was ensured . at the end of surgery
a standard postoperative regime consisting of topical prednisolone acetate 1% ( pred forte , allergan , usa ) 4 times a day for 5 days tapering over 2 weeks and topical gatifloxacin 0.3% ( zymaxid , allergan las , irvine , usa ) 4 times a day for 2 weeks was started .
timolol maleate eyedrops 0.5% ( timolet , sun pharmaceuticals , india ) was also started 2 times per day for 3 days .
postoperatively , the patient was examined at 4  h to check for proper icl positioning and vaulting on slit lamp , and iop was checked .
the patient was then followed on postoperative day 1 , 1 week , 1 month , 3 months , 6 months , and 9 months .
the main surgical outcomes were evaluated at 1 , 3 , 6 , and 9 months follow - up . at each of these visits , udva , cdva , mse , iop , icl vaulting , and ecc were evaluated .
icl vault was measured by anterior segment optical coherence tomography ( as - oct ) rtvue ( model - rt100 version 6.9 , fremont , usa ) .
patients were asked about subjective symptoms of glare and haloes at the end of follow - up period of 9 months .
the safety index was calculated by dividing the postoperative cdva ( in decimal ) at 9 months by the preoperative cdva ( in decimal ) .
the efficacy index was calculated by dividing the postoperative udva ( in decimal ) by the preoperative udva ( in decimal ) .
the data were analyzed using spss version 20 ( statistical package for social sciences ) with paired t - test for intragroup comparison and mann whitney u value test for intergroup comparisons .
a total of 62 eyes of 32 patients with a mean    sd age of 24.56    4.8 years underwent v4b icl implantation ( 21 non - toric , 41 toric icl - ticl ) with intraoperative peripheral iridectomy ( pi ) , and 10 eyes of 5 patients with a mean    sd age of 26.13    3.8 years had implantation of v4c icl with central hole ( p  =  0.81 ) ( 4 non - toric , 6 ticl ) .
the large difference in the number of eyes in the two groups is due to the later development of the v4c model .
the mean preoperative manifest spherical equivalent ( mse ) was 9.98    2.8 d and 9.14    2.4 d in the v4b and v4c groups , respectively ( p  =  0.51 ) , which reduced to postoperative values of 0.24    1.3 d and 0.2    1.18 d , respectively ( p  =  0.09 ) .
the mse reduced significantly in the two groups ( p  <  0.001 in both the groups ) .
the mean preoperative astigmatism was 1.7    1.5 diopter cylinder ( dcyl ) and 1.8    1.5 dcyl which respectively reduced to 0.7    0.7 dcyl and 0.8    0.4 dcyl at 9 months ( p  <  0.001 in both the groups ) ( table 1 ) .
a gain of 1 line of cdva was seen in 10% and 11.76% eyes in v4b and v4c groups , respectively ( p  =  0.08 ) , while no change in cdva was seen in 90% and 88.24% of eyes ( p  =  0.07 ) .
no eye had loss of lines of cdva post surgery . at the end of 9 months
follow - up , mean ecc loss was 6.4% and 6.1% ( fig .  1 , fig
.  2 ) ( p  =  0.08 ) , mean vault was 573.13    241.13   , and 612    251.14   , respectively , in the v4b and v4c groups ( p  =  0.02 ) ( fig .  3 ) .
anterior subcapsular opacities were present in 6.9% and 3.14% of eyes with v4b and v4c groups , respectively ( p  <  0.01 ) .
four eyes from v4b ( 9.75% ) and 1 eye from v4c ( 16.66% ) groups had rotation of more than 30 and required re - alignment surgery which was done successfully ( fig .  4 ) . two eyes ( 3.22% ) with v4b icl implantation
had high postoperative iop ( > 35  mm hg ) due to blocked pi and required nd : yag laser iridotomy which was done with successful control of iop .
the safety indices were 1.11 and 1.14 and efficacy indices were 1.4 and 1.5 in the v4b and v4c groups , respectively , at the end of 9 months . at the end of 9 months , on questioning , the most common subjective symptom reported was glare and haloes in 23% and 25% in the two groups , respectively ( p  =  0.09 ) . however , they were not annoying enough to cause visual disability . due to the large difference in the sample size between the two groups ,
the results of the intergroup comparisons done by the mann whitney u value test with p values is limited and need to be considered accordingly .
phakic intraocular lens implantation is so far the only refractive treatment for high myopia that offers preservation of accommodation and potential reversibility . in our study
, we found that both the types of icl with or without the central hole showed a satisfactory visual outcome which was maintained at the end of 9 months follow - up period .
. also found similar results with the two models with both providing good visual outcome and no difference in the objective scatter index and higher order aberrations .
icls have emerged as a successful and promising modality for the treatment of moderate to high myopia especially in candidates unsuitable for laser refractive procedures.10 , 11 though being an intraocular procedure , it provides the advantage of reversibility and an acceptable safety profile . with the advent of toric icl , a significant amount of astigmatism can be corrected .
the ticl have shown to be stable over a long term period with the haptics enforcing stable lens position in the ciliary sulcus .
the ticl is fundamentally different from toric intraocular lenses as it is not subject to contraction of the capsular bag .
the soft footplates of the icl conform to the normal undulating contours of the ciliary sulcus with a kind of lock - and - key situation where the footplates will drape over and into the tiny irregular features of the sulcus .
, we had 4 from v4b ( 9.75% ) and 1 eye from v4c ( 16.66% ) groups requiring realignment surgery with successful outcomes .
found an incidence of 1.7% of rotation in excess of 10 with 98.3% showing excellent rotational stability without decrease in visual acuity .
the iop was maintained below 21  mm of hg in both the groups over 9 months .
higueras - esteban et  al . found no significant changes between the v4b and v4c models with respect to iop stability .
studied the fluid dynamics of aqueous humor in v4c model and suggested that hole - icls improve the circulation of aqueous humor to the anterior surface of the crystalline lens .
sanders reported approximately 67% of eyes developing anterior subcapsular opacities at 7 year following icl implantation but only 12% had progressed to clinically significant cataract in the same period , especially in high myopes and older patients .
fernandes et al . also found cataract as the major complication . in our study ,
none of the eyes had visually significant cataract at the end of 9 months follow - up period . in a study conducted by pothireddy et al . in india ,
the safety index was 0.75 , and the efficacy index was 1.04 twelve months postoperatively .
icl was thus evaluated to be a safe and effective procedure in terms of visual outcome .
pineda - fernandez et al . reported mse in 61.1% and 22% of eyes within 1.00 d and 0.50 d of emmetropia . in their study , the mean residual sphere was 0.25 d , and mean residual cylinder was 0.12 dcyl .
insignificant refractive change during follow - up after icl implantation with similar results was obtained by igarashi et al .
demonstrated rapid cell loss until 1 year postoperatively , after which the rate of loss was no longer statistically significant.20 , 21 in our study , the vitrector pi had clean cuts with minimum pigment dispersion and a chance of being incomplete or getting blocked .
iop was stable throughout the 9 months of follow - up in both the groups . in the v4c group , this could be attributed not just to the centraflow technology , but also to the negligible pigment dispersion due to avoidance of pi .
none of our cases developed secondary glaucoma following excessive vault or pigment dispersion during the follow - up . in our study ,
the icl vault was maintained at 9 months follow - up period.22 , 23 kamiya et al .
found the vault of the new central hole piol to be essentially equivalent to the vault of the conventional piol , suggesting that the presence of the central hole did not significantly affect the vault or the refractive accuracy .
kamiya et al.25 , 26 found the v4c icl with aquaport essentially equivalent in the optical quality variables to conventional icl implantation .
they suggested that the presence of the central artificial hole does not significantly affect the optical quality and the intraocular scattering after surgery .
other studies27 , 28 , 29 , 30 have also found good optical quality results with v4b and v4c icls .
studied piols and found that v4b icl implantation leads to decreased night vision performance with glare and haloes .
many studies33 , 34 , 35 , 36 , 37 , 38 have shown good visual performance and quality of life after icl implantation . in our study , patients in both groups experienced glare and haloes , but they were visually insignificant and non - annoying .
icl thus offers a safe , effective , and reversible option for correction of high myopia .
however , evaluation of the incidence of cataract formation and endothelial cell loss over a decade should be carried out .
the small sample size and unequal number of patients in the two groups precludes definite conclusion .
also , including both eyes of one patient in the study , limits the conclusion .
icl with a central hole offers an added advantage of annulling a pi and providing a stable iop .
however , a larger sample size undergoing v4c implantation with a longer follow - up is required for confirming the results .
 purposeto evaluate the visual outcome and intraocular pressure changes after visian implantable collamer lens ( icl ) implantation v4b and v4c ( with central hole ) for correction of high myopia.methodsa prospective , consecutive , interventional comparative case series of v4b and v4c icl implantation was done in high myopic patients who were unsuitable for laser vision . 
 the main outcome measures studied were uncorrected and corrected distant visual acuity ( udva , cdva ) , icl vault , intraocular pressure ( iop ) , endothelial cell count ( ecc ) , and development of subcapsular lens opacities . 
 the patients were evaluated at postoperative 1,3,6 , and 9 months.resultsa total of 62 eyes of 32 patients ( 24.56    4.8 years ) underwent v4b icl implantation ( 21 non - toric , 41 toric icl - ticl ) with intraoperative peripheral iridectomy ( pi ) , and 10 eyes of 5 patients ( 26.13    3.8 years ) had implantation of v4c icl ( 4 non - toric , 6 ticl ) . 
 the mean preoperative manifest spherical equivalent ( mse ) was 9.98    2.8 d and 9.14    2.4 d in the v4b and v4c groups , respectively , which reduced to postoperative values of 0.24    1.3 d and 0.2    1.18 d , respectively . at the end of 9 months 
 follow - up , mean ecc loss was 6.4% and 6.1% , mean vault was 573.13    241.13   , and 612    251.14   , respectively , in the v4b and v4c groups . 
 anterior subcapsular opacities were present in 6.9% and 3.14% of eyes with v4b and v4c groups , respectively . 
 four eyes from v4b ( 9.75% ) and 1 eye from v4c ( 16.66% ) had rotation of more than 30 and required realignment surgery , which was done successfully . 
 two eyes ( 3.22% ) with v4b icl implantation had high postoperative iop ( > 35  mm hg ) due to blocked pi and required nd : yag laser iridotomy , which was done with successful control of iop . 
 the safety indices were 1.11 and 1.14 , and efficacy indices were 1.4 and 1.5 in the v4b and v4c groups , respectively , at the end of 9 months.conclusionicl implantation is a safe and effective surgery for correction of high myopia . 
 implantation of icl with a central hole showed negligible postoperative iop fluctuations without a peripheral iridectomy . 