keratoconus is a progressive , noninflammatory ocular disorder characterized by steepening and distortion of the cornea , apical thinning , and central scarring . spectacles are useful in optical management of the early stages of keratoconus when the astigmatism is mild . however , for moderate - to - advanced keratoconus , spectacles are not very useful for improving vision [ 4 , 5 ] . in this stage of the disease , various options for contact lenses are available such as rigid gas permeable ( rgp ) lenses [ 6 , 7 ] , hybrid contact lenses [ 8 , 9 ] , piggyback lenses [ 10 , 11 ] , and scleral lenses [ 12 , 13 ] . rgp lenses are traditionally the first choice and have been commonly used because of their success in improving visual acuity . rpg lenses improve visual acuity by their refractive power and also by providing a regular corneal surface . however , prolonged use of rgp lenses may lead to lens intolerance and ocular discomfort in most patients with keratoconus . another important disadvantage of rpg lenses is the potential for damage to the cornea [ 15 , 16 ] . also sometimes , it is not possible to find the suitable rgp contact lens for each irregular corneal surface . in such cases , soft contact lenses should be considered . toris k ( swisslens , prilly , switzerland ) is an example of these kinds of lenses for keratoconus . soft contact lenses have their comfort advantages over rgps but they do not provide a regular corneal surface as much as rgp lenses do . in this study , we aimed to evaluate the comfort and visual performance of toris k soft contact lens in patients with moderate - to - advanced keratoconus . we also aimed to compare the visual performance of the contact lens in different cone shape ( oval , nipplei globus ) , cone location ( central , paracentral ) , and severity of the disease ( moderate , advanced ) . in this retrospective study , we reviewed the records of patients with keratoconus who were fitted torsi k contact lenses between december 2013 and december 2015 . the study adhered to the tenets of the declaration of helsinki and local ethic committee approval was obtained . to be included in the study , each patient was required to have all of the following criteria : age  18 years , a diagnosis of moderate - to - advanced keratoconus detected by thorough topographic evaluation in conjunction with the clinical examination , and mean corneal power > 45 diopters ( d ) . patients were not included in the study if they had a history of ocular surgery , history of ocular trauma , and any ocular disease ( e.g. , active ocular infection , clinically significant nuclear sclerosis / cataract , and retinal diseases ) that might affect the results , and break - up time ( but ) under 10 seconds . data collected from the patients ' records included age , gender , refractive errors , but , mean - steep - flat keratometric measurements and cone type - location from sirius ( schwind eye - tech - solutions gmbh & co. kg , kleinostheim , germany ) scan , uncorrected visual acuity ( ucva ) , best spectacle corrected visual acuity ( bcva ) , best contact lens corrected visual acuity ( bclcva ) , base curve ( bc ) prescribed contact lens diopter , and visual analogue scales ( vas ) . all participants underwent a standardized ophthalmologic examination including refraction , visual acuity ( snellen from 6 meters via topcon acp-8 chart projector ( topcon corporation , tokyo , japan ) under photopic condition ( 85  cd / m ) luminance ) , slit - lamp biomicroscopy - fundoscopy , but , and corneal topography via sirius . after ucva and bcva were measured , contact lens was fitted as provided in its technical fitting guide and manufacturer 's specifications were followed ( table 1 ) . a dedicated set of lenses is needed for this purpose in different base curves and different peripheral radii with power . the lens was allowed to settle for approximately 5  min and then the movement , rotation , and centration were checked with a slit - lamp . after correct fit and patient comfort were achieved , residual refractive error was measured via retinoscopy . bclcva and vas score were measured a week later at the first visit of patients . vas is previously used to rate comfort with contact lenses [ 14 , 17 ] . vas were administered by asking patients to record their subjective impressions of vision and comfort using a scale from 0 ( lowest ) to 10 ( highest ) . the scale was horizontally oriented , measuring 10  cm , and the value for statistical analysis was measured with a rule at the point where the mark was inserted by the patient . in this study , according to the topographic map , cone location was classified as central ( if the highest power was located in central 2  mm ) and paracentral ( if the highest power was located out of central 2  mm ) . with keratoconus classified based on the mean k reading on corneal topography , the patients were classified as mild in cases with k value less than 45  d , moderate in cases with k value between 45 and 52  d , and advanced in cases with k value more than 52  d [ 18 , 19 ] . primary outcome measures included ucva , bcva , bclcva , vas , and results in subgroups according to cone location and severity of keratoconus . visual acuity was converted to the logarithm of the minimum angle of resolution ( logmar ) for statistical analysis . categorical variables were presented as numbers and percentages , while numerical variables were expressed as the mean and standard deviation . the outcomes were compared using appropriate tests ( paired - samples t - test , independent - samples t - test , and one - way anova ) . the statistical package for the social sciences version 23 ( spss , chicago , il , usa ) was used for data analysis , for which values of p < .05 were considered to be statistically significant . the study sample consisted of 60 eyes of 40 participants ( 17 females and 23 males ) , all of whom were caucasian . the mean age was 27.3  8.6 years ( range : 18 to 54 ) . hydrocone k34 lenses were used for all participants . the mean base curve ( bc ) was 7.75  0.15 ( range : 7.40 to 8.20 ) . the mean spherical and cylindrical power ( d ) of prescribed contact lens were 2.89  2.43 ( range : 10 to 1 ) and 2.02  1.08 ( range : 4.25 to 0 ) . when we divided the patients into subgroups according to cone type , there was no significant difference in ucva and bcva between groups ( p = .091 , p = .817 , one - way anova ) but there was a significant difference in bclcva between groups ( p = .029 , one - way anova ) . post hoc tukey test showed that bclcva was significantly better in oval type than globus type ( p = .022 ) . when we divided the patients into subgroups according to cone location , there was no significant difference in ucva , bcva , and bclcva between groups ( p = .610 ; p = .630 ; p = .468 ( independent - samples t - test ) ) . when we divided the patients into subgroups according to the severity of keratoconus , ucva and bclcva were significantly better in moderate keratoconus group ( p = .015 , p = .018 , independent - samples t - test ) . the mean line gain in snellen between bcva and bclcva was 3.6  1.8 lines ( range : 07 lines ) . 45 patients ( 75% ) gained 3 or more lines with contact lens correction against spectacle correction . there was no significant difference in the mean line gain between moderate keratoconus group and advanced keratoconus group ( p = .104 , independent - samples t - test ) . the mean line gain was higher in central cone group than paracentral cone group ( p = .014 , independent samples t - test ) . there was significant difference in the mean line gain between oval - nipple - globus groups ( p = .045 , one - way anova ) . the post hoc tukey test showed that the difference was between oval and globus type and the mean gain line was significantly higher in oval group ( p = .045 ) . contact lenses have an important role in the management of visual symptoms of patients with keratoconus . the purpose of fitting contact lenses in such patients is to improve visual acuity with comfort . it is well known that rpg contact lenses produce good visual acuity results and improve patients ' quality of life . . showed that rpg contact lenses may cause some serious complications such as corneal erosion , hidrops , allergic conjunctivitis , and dry eye . another downside of rpg lenses is that many patients can not tolerate them because of comfort issues . soft contact lenses are known for comfort and they may be a good alternative to rgp lenses in patients who experienced intolerance to rgp lenses . gumus and kahraman reported results of toris k contact lens in keratoconus . in their study , comfort score was classified as good / excellent in 46 eyes ( 92% of participants ) and moderate in only 4 eyes ( 8% of participants ) . the high vas score provides strong evidence that patients who can not tolerate rgp lenses due to discomfort may find toris k contact lens an acceptable option . in gumus and kahraman study , the mean increase in visual acuity was reported 4.5 lines ( range : 1 to 9 lines ) . 92% of their participants classified their visual acuity as good / excellent in daytime , and 76% were classified as good / excellent in nighttime . in the present study , the mean visual acuity was significantly better with the contact lens than with spectacles and improved to 0.16  0.20 logmar from 0.47  0.27 logmar . good visual results show to us that toris k is effective for treatment of visual symptom of moderate - to - advanced keratoconus . this study is the first study in literature that compares the visual results of toris k contact lens fitting in keratoconus subtypes ( cone type , cone location , and severity of keratoconus ) . results show us that bclcva and the mean line gain were better in oval cones than globus cones ( figure 2 ) . however , we believe that visual management of globus type cones is harder than other types with soft contact lenses and another contact lens type or surgical options may be necessary . the mean visual acuity with contact lens was better in moderate keratoconus group than advanced group . it is proved that contact lens vision correction is more successful at the early stages of the disease . showed that the cone location has no effect on the rgp corrected visual acuities in patients with keratoconus . similarly , this study showed that the cone location ( central or paracentral ) has no effect on the toris k soft contact lens corrected visual acuities . also this study does not show the lens behaviors , complications , in the long term . it is well - known that soft contact lenses are thick and cause some complications , due to hypoxia , such as corneal swelling , contact lens induced papillary conjunctivitis , and superior punctuate keratitis [ 24 , 25 ] . the strongest aspect of the study is that being first report in the literature that examines the visual results of toris k contact lens in different subtypes ( cone type , cone location , and severity of keratoconus ) of keratoconus . finally , reduced sample size in some subgroup comparisons may count as a limitation . in sum , toris k contact lenses may improve visual acuity with comfort in patients with keratoconus . further studies with longer follow - up period that compared the different soft contact lenses are needed .
objectives . to evaluate the visual performance of toris k soft contact lenses in patients with moderate - to - advanced keratoconus and also to compare the results according to cone types , cone location , and severity of keratoconus . materials and methods . 
 sixty eyes of 40 participants were included in this retrospective study . 
 uncorrected visual acuity ( ucva ) , best - spectacle corrected visual acuity ( bcva ) , best - contact lens corrected visual acuity ( bclcva ) , and comfort rating via visual analogue scales ( vas ) were measured . 
 results . 
 the mean age was 27.3  8.6 years ( range : 18 to 54 ) . 
 the mean logmar ucva , bcva , and bclcva were 0.85  0.38 ( range : 0.301.30 ) , 0.47  0.27 ( range : 0.101.30 ) , and 0.16  0.20 ( range : 01.00 ) . 
 there were significant increases in visual acuities with contact lenses ( p < .05 ) . 
 bclcva was significantly better in oval type than globus type ( p = .022 ) . 
 ucva and bclcva were significantly better in moderate keratoconus group ( p = .015 , p = .018 ) . 
 the mean line gain in snellen was 3.6  1.8 lines ( range : 07 lines ) . 
 the mean line gain was higher in central cone group than paracentral cone group and oval group than globus group ( p = .014 , p = .045 ) . 
 the mean vas score was 8.14  1.88 ( range : 610 ) . conclusions . 
 toris k can improve visual acuity of patients with keratoconus . 
 toris k is successful even in the moderate and advanced form of the disease .