a cataract increases lens opacity and reduces visual acuity ( va ) , thus impairing the patient 's quality of life .
various techniques for cataract surgery have been developed since h. ridley introduced intraocular lenses ( iols ) composed of polymethylmethacrylate in 1949 .
the stability of iols allows cataract surgery to be commonly performed worldwide , and technological advancements such as multifocal and toric iols have increased the procedure 's popularity [ 6 , 7 ] . to improve quality of life , cataract surgery
postoperative va , contrast sensitivity , and optical aberrations were measured as objective indices of surgical success [ 1116 ] .
after cataract surgery , improvement in va is typically tested with a high - contrast ( 100% ) chart under photopic and mesopic conditions .
for example , visual inspection of human faces  of the utmost importance in daily life  involves a target of large size and low contrast . the change in va after cataract surgery has not been studied under various levels of contrast .
the aim of this study was to assess the visual performance of pseudophakic eyes after cataract surgery at different contrast levels by using the oqas ( optical quality analysis system , visiometrics , terrassa , spain ) .
this research was approved by the institutional review board of the catholic medical center at the catholic university of korea and conducted in accordance with ethical research guidelines .
the present study adhered to the declaration of helsinki and was approved by the institutional review board of the catholic medical center at the catholic university of korea ( approval number : kc12risi0023 ) .
patients completed an informed consent form approved by the institutional review board after the purpose of the study was explained to them .
no patients had a history of ocular surgery , ocular disease , or general disorders affecting vision ( e.g. , diabetic retinopathy ) .
vision of patients greater than 0.1  logmar was measured using the snellen test and classified as age - matched ( 50s , 60s , and 70s ) between normal and pseudophakic eyes .
the patients with pseudophakic eyes had undergone phacoemulsification and received one of five iol types in the posterior chamber 26 months before the study .
patients were stratified into the following age groups : 5059 years , 6069 years , and 7079 years .
patients with failed iol implantation into the lens capsule , severe posterior lens capsule opacification or history of laser capsulotomy due to opacification , or any other eye complication were excluded .
those with poor cooperation were also excluded . to prevent uncorrected refractive error from limiting contrast sensitivity or va [ 20 , 21 ] ,
va was measured using a snellen chart at 6  m. altered contrast sensitivity was simulated with the oqas by using the double - pass technique . with this approach , the retinal image , degree of haze inside the eye , and condition of visual function
are analyzed in terms of objective scattering index ( osi ) , modulation transfer function ( mtf ) cut - off value , and strehl ratio , respectively [ 2225 ] .
simulated va by oqas was evaluated at contrast of 100% , 20% , and 9% .
testing at each contrast level was performed for all five types of iols : hoya pc-60ad ( hoya , corp , tokyo , japan ) , ec-1pal ( aaren scientific , ontario , canada ) , akreos mi-60 ( bausch & lomb , rochester , ny , usa ) , ny-60 ( hoya , corp , tokyo , japan ) , and xl stabi zo ( carl zeiss meditec , jena , germany ) .
analysis of variance ( anova ) and independent - sample t - tests were performed using spss version 18.0 software ( ibm corporation , armonk , ny ) .
the subjects ' characteristics are shown in table 1 . mean visual acuities for the normal eyes were 0.16  0.18  logmar , 0.30  0.18  logmar , and 0.52  0.17  logmar at 100% , 20% , and 9% contrast , respectively ( table 2 ) .
in normal eyes from all age groups , simulated va decreased significantly when contrast was reduced ( 5059 , p = 0.000 ; 6069 , p = 0.000 ; 7079 , p = 0.020 ) . however , simulated va was highest among those aged 5059 and lowest among those aged 7079 .
simulated va at 100% and 9% contrast decreased with increasing age ( 100% , p = 0.045 ; 9% , p = 0.010 ) .
no significant differences were noted among the age groups at 20% contrast ( p = 0.070 ) . for pseudophakic eyes ,
mean visual acuities were 0.16  0.12  logmar , 0.33  0.20  logmar , and 0.56  0.21  logmar at 100% , 20% , and 9% contrast , respectively ( table 3 ) .
as in the normal eyes , va decreased significantly when contrast was reduced ( p = 0.000 ) . however , nova was similar in all age groups ( p > 0.05 ) . 

figure 1 shows simulated va for the normal and pseudophakic eyes in each age group at all contrast levels .
however , among those aged 7079 , the pseudophakic eyes exhibited significantly higher va ( p = 0.000 ) . 
 table 4 shows the simulated mean visual acuities of the pseudophakic eyes according to iol type .
subjects implanted with ec-1pal and ny-60 iols showed the lowest and the highest va , respectively , although no significant differences were noted among iols at any contrast level .
regardless of iol type , va decreased significantly when contrast was reduced ( p = 0.000 ) .
osi value , mtf cut - off value , and strehl ratio values are presented in table 5 .
the mean values were 2.21  1.38 , 23.29  10.72 , and 0.18  0.47 , respectively , in the pseudophakic group and 1.99  1.41 , 23.41  9.72 , and 0.13  0.07 , respectively , in the normal group .
the only significant finding was elevated osi values in normal eyes from the 7079 age group ( p = 0.008 ) .  
figure 2 shows representative oqas results obtained from a 69-year - old patient with normal eyes and a 72-year - old patient with pseudophakic eyes .
in addition to questionnaires , va and contrast sensitivity assessments are used to evaluate ocular health after cataract surgery .
recent technological advancements have allowed for the measurement of higher - order aberrations including spherical aberration and coma aberration   as well as the optical analysis of light spread within the eye ( point spread function ) [ 2729 ] . however , such tests are useful only in characterizing symptoms .
.   used the oqas to measure the osi , mtf cut - off value , and strehl ratio after cataract and refractive surgeries and to assess visual function objectively .
, we investigated vision at three contrast levels simulated using the oqas and stratified subjects with normal and pseudophakic eyes by age . among patients in their 50s and 60s , normal eyes exhibited sim va superior or similar to that of pseudophakic eyes
however , among those in their 70s , pseudophakic eyes had significantly superior va ( p = 0.000 ) .
alternatively , the normal eyes in this age group may have been free of any lens opacity that could be detected by slit - lamp examination but may have had fine opacities in the lens and/or vitreous chamber that scattered light , thereby reducing va .
another significant finding was the lower osi value of the pseudophakic eyes in this group ( p = 0.008 ) , which is in line with the report by saad et al .   that osi values increase with age in normal eyes .
in both the normal and pseudophakic groups , va was directly related to contrast level regardless of age .
furthermore , va decreased as age increased ; as reported by mathai et al .  
sim va was similar in normal and pseudophakic eyes of subjects aged 5069 but superior in the pseudophakic eyes of subjects aged 7079 years .
therefore , visual function must have returned to normal levels in all patients with iols at 26 months after cataract surgery .
the ny-60 and ec-1pal iols were associated with the highest and lowest visual acuities , respectively , regardless of contrast level .
interestingly , use of the ny-60 iol is reportedly associated with fewer capsular folds than use of a three - piece iol .
ny-60 iol users also report the absence of entoptic phenomena   1 year after surgery .
in an eye with an iol , the presence of entoptic phenomena correlates directly with the osi value .
this relationship may explain the superior va of the ny-60 group , although this improvement in va was associated with use of the acrysof sn60wf and tecnis zcb00 iols in previous reports . in this study ,
reduced contrast was associated with decreased acuity across groups , but no significant difference in simulated va among iol types was noted at any contrast level ( p = 0.413 ) .
a possible limitation of our study is that the oqas 's he - ne diode laser may have introduced error to the osi readings , for example , in patients with dry eye symptoms or cloudy vitreous , which scatters light .
in summary , va at 26 months after cataract surgery in pseudophakic eyes is similar to that of normal eyes and older patients with pseudophakic eyes have superior simulated va to age - matched controls , contrary to previous reports that the level of contrast and age affect visual function .
these findings suggest that iols ensure simulated va similar to that of the normal eye even in very low - contrast conditions , as encountered when driving at night .
therefore , iol implantation should have a beneficial impact on the patient 's quality of life .
the oqas seems to be a useful instrument for the objective evaluation of visual quality under contrast after various surgeries such as cataract surgery , laser - assisted in situ keratomileusis ( lasik ) , laser - assisted subepithelial keratectomy ( lasek ) , and keratoconus surgery .
 
 purpose . to assess visual function using optical quality analysis system ( oqas ) at varying levels of contrast in pseudophakic eyes 
 . methods . the study included 
 patients admitted to seoul st . 
 mary 's hospital between january and february 2012 : 143 pseudophakic eyes with one of five intraocular lens types , examined 26 months after cataract surgery , and 93 normal eyes ( enhanced visual acuity ( va ) < 0.1  logmar ) in age - matched controls . 
 subjects were examined at three contrast levels using the oqas . 
 results . at 100% , 20% , and 9% contrast , simulated mean va was 0.16  0.18  logmar , 0.30  0.18  logmar , and 0.52  0.17  logmar , in normal eyes , and 0.16  0.12  logmar , 0.33  0.20  logmar , and 0.56  0.21  logmar , respectively , in pseudophakic eyes . 
 simulated va decreased significantly when contrast was reduced , regardless of ocular status , age group , and lens type ( p < 0.05 ) . 
 there were no significant differences between normal and pseudophakic eyes among subjects aged 5069 ( p > 0.05 ) . among subjects aged 7079 , pseudophakic eyes showed improved simulated va ( p = 0.000 ) and objective scattering index values ( p = 0.008 ) 
 . conclusions . patients with intraocular lenses have similar or superior visual function when compared to those with normal eyes at 26 months after cataract surgery , even under low - contrast conditions . 
1. Introduction
2. Materials and Methods
3. Results and Discussion
4. Conclusion