studies have demonstrated that photorefractive keratectomy ( prk ) and laser in situ keratomileusis ( lasik ) for myopia are safe and predictable .
the application of excimer laser for the treatment of hyperopia started in the late 90s.13 in this process , a paracentral meniscus of the corneal stroma is removed to steepen the central cornea .
initially , prk with the excimer laser was used to corrected hyperopia . however , postoperative corneal haze restricted prk for hyperopia , and eventually lasik became the most common method for the correction of hyperopia .
lasik , however , has certain limitations and drawbacks such as flap related complications,4 dry eye,5 and keratectasia.6 in addition , patients at risk of trauma and/or those with thin corneas are not eligible for lasik .
the prevention of corneal haze with mitomycin - c ( mmc)7 has resulted in the resurgence of prk for keratorefractive surgery . the outcomes of hyperopic prk have been promising ; however , the predictability is lower , compared to myopic prk .
published results indicate comparable efficacy for prk and lasik for the correction of up to 4.00 d of hyperopia.891011121314151617 however , few studies have assessed the outcomes of hyperopic prk with the application of mmc ( prk - mmc ) .
here , we present 1-year outcomes and complications with hyperopic prk - mmc for the treatment of mild to moderate hyperopia .
from december 2009 to december 2010 , consecutive cases of hyperopia undergoing prk - mmc were approached .
all excimer ablations were done using either the allegretto wave concerto ( alcon inc . , fort worth , tx , usa ) or the technolas 217-z ( bausch and lomb inc .
preoperatively , all patients were at least 20 years of age , and they had stable refraction in the past 18 months ( < 0.50 diopters [ d ] change ) .
none of the patients had any history of ocular surgery , connective tissue disorders , or diabetes , and they were not using any medication that might interfere with wound healing .
soft contact lens users stopped wearing lenses three days before examinations , patients wearing hard contact lenses were advised to stop using the lenses for at least 3 weeks before their appointment .
preoperative examinations included assessment of visual acuity with and without correction , manifest and cycloplegic refraction , measurement of the central corneal thickness with an ultrasound pachymeter ( nidek , us-1800 echoscan ) , slit lamp examination , corneal topography ( eyesys vision , eyesys 3000 ) , fundus examination , and measurement of the intraocular pressure . in cases with a considerable discrepancy between manifest and cycloplegic refraction , manifest refraction was repeated after the effect of cycloplegic drops had receded to allow greater correspondence between refraction . the maximum acceptable difference between manifest and cycloplegic
refraction was 1.00 d. surgery was performed under topical anesthesia with tetracaine 0.05% eye drops .
a hockey knife spatula was used to mechanically remove the epithelium in the central 8.0 mm of the cornea , and the laser ablation was delivered to the surface . for those over 40 years of age , the correction was based on full cycloplegic refraction , and in younger patients , we used the average of cycloplegic and subjective refractions .
treatments with the concerto excimer laser were programmed for an optical zone of 6.5 mm and a transition zone of 1.25 mm .
treatments with the technolas laser were programmed for an optical zone of 6.0 mm with 1.0 mm for the transitional zone .
once the ablation was completed , 0.02% mmc solution was applied to the ablated area for 120 s,15 and then the entire corneal surface and conjunctiva was rinsed with 20 ml cold normal saline .
subsequently , chloramphenicol drops were instilled , and surgery was concluded by applying a bandage contact lens ( air optix ; novartis ag , basel , switzerland ) .
postoperative medications included 0.5% chloramphenicol eye drops , four times daily , until complete re - epithelialization , and 0.1% betamethasone eye drops four times daily for the first two weeks which there replaced with 0.1% fluorometholone drops four times daily for the next 6 weeks ( a total of 8 weeks ) .
patients had follow - up visits every day until re - epithelialization was complete and were scheduled to be examined at 1 , 3 , 6 , and 12 months , postoperatively . at
each follow - up visit data were collected on the best corrected distance vision acuity ( bcva ) and uncorrected distance vision acuity ( ucva ) , manifest refraction , and slit lamp examination , and any complication such as infection , ectasia , or haze formation .
the protocol of this study was approved by the institutional review board of noor ophthalmology research center , and all patients signed informed consents before enrollment .
quantitative variables are summarized as a mean and standard deviation . to compare results at preoperatively and postoperatively we used the repeated measures analysis of variance .
the mean age of the patients was 44.8  11.3 years ( range , 2055 years ) and eight cases ( 19% ) were under 40 .
preoperatively , mean manifest refractive spherical equivalent ( mrse ) was + 2.00 d  0.76 d ( range , 0.54.0 d ) and mean spherical error was + 2.57 d  0.87 d ( range , 1.255.5 d ) .
figure 1 presents the changes in corrected and uncorrected visual acuity , and figure 2 demonstrates changes in mean mrse .
meansd ( range ) of spherical and cylinder error ( diopters ) at different visits during a 1-year follow - up logarithm of the minimum angle of resolution uncorrected distance visual acuity and best spectacle - corrected distance visual acuity preoperatively and at 1 , 3 , 6 , and 12 months after surgery stability of hyperopic photorefractive keratectomy with mitomycin - c out to 12 months postoperatively table 1 presents changes in sphere and cylinder errors due to each laser .
changes in spherical ( 0.073 ) and cylindrical ( 0.197 ) errors were not significantly different between devices [ table 1 ] .
one month after surgery , a mean spherical error was myopic but decreased toward emmetropia .
there were significant changes in the spherical error preoperatively to 1-month postoperatively ( p < 0.001 ) , as well as from 1 to 3 months postoperatively ( p = 0.024 ) .
postoperatively , both spherical error and mrse were significantly different from the preoperative values ( p < 0.001 ) ; 69.0% were within  0.50 d , and 98.0% were within  1.00 d of emmetropia . at this time , 18 eyes ( 42.9% ) had ucva of 20/20 , and in 39 eyes ( 92.8% ) ucva was 20/40 or better .
the best spectacle - corrected distance visual acuity ( bcva ) increased by two lines in three eyes ( 7.1% ) and one line in two eyes ( 4.7% ) , 31 eyes ( 73.8% ) showed no change , three eyes ( 7.1% ) lost one line , and three other eyes ( 7.1% ) lost two lines of corrected vision [ figure 3 ] .
thirty - one eyes showed no change , two lost two lines , and two gained two lines no stromal haze was observed in the central cornea . during the first 6 months , two eyes ( 5.0% ) had peripheral haze ( hanna grade 1 ) which resolved by the 12-month follow - up visit .
slight haze was detected in 15 eyes ( 36.0% ) and resolved in all cases within a few months .
there was no case of ectasia or need for retreatment during the 1-year follow - up .
microbial keratitis occurred in one eye which was eliminated from the study and final analysis .
in this study , we evaluated the safety , efficacy , stability , and predictability of hyperopic prk over 1-year .
unlike myopia , one of the challenges in making hyperopic corrections is the difference between manifest and cycloplegic refractions , especially in prepresbyopic patients .
this issue is less significant in hyperopia over 5.0 d , where the latent component is lower . in a young patient
, corrections based on manifest refraction will result in a late hyperopic shift while treating the full cycloplegic refraction will result in myopia .
esquenazi and mendoza12 suggested using manifest refraction when there is more than 0.50 d discrepancy between manifest and cycloplegic refractions , but this could result in residual latent hyperopia in young patients .
jackson et al.18 recommended using only manifest refraction in a young patient and accept some regression and latent hyperopia .
spadea et al.19 based the laser correction according to the cycloplegic refraction in patients under 40 years of age , allowing for up to 0.5 d difference between the cycloplegic and manifest refractions . in cases over 40 years , they19 based corrections on manifest refraction .
we used the cycloplegic refraction as the correction target in patients over 40 and the average of cycloplegic and manifest refractions in younger cases , and we allowed for up to 1.00 d of difference between cycloplegic and manifest refractions .
it seems that less difference between the two refractions should be allowed before correction . at 12 months
postoperatively , 43% of our patients had 20/20 ucva , which is comparable to jackson et al .
's study18 ( 52% at 12 months ) and spadea et al. s study19 ( 46% at 24 months ) . in this study ,
the safety index ( postoperative bcva / preoperative bcva ) was 1.00 , and the efficacy index ( postoperative ucva / preoperative bcva ) was 0.88 , which were comparable to 0.95 and 0.87 values reported by leccisotti.14 however , despite a safety index of 1.00 , we had six eyes with one or two lines loss in bcva which could partly be due to loss of previous linear magnification of spectacles14 or irregular astigmatism caused by some apical nodular subepithelial haze.20 stability of refraction after hyperopic prk has been reported in most studies to occur sometime between 3 and 12 months after surgery . in our report ,
however , stevens and ficker,22 reported that it took about 12 months for the refraction to stabilize .
these discrepancies can be due to different magnitudes of preoperative hyperopia in these studies because higher hyperopic corrections require longer stabilize .
review of our study in comparison to other studies on the correction of hyperopic photorefractive keratectomy mrse within  1.00 d of the intended refraction has been reported in different studies to be between 67% and 100% .
we found it was 98% , this can be attributed to better predictability with newer generations of excimer laser machines with larger ablation zones and improved ablation profiles.1223 in hyperopic prk , the central corneal stroma largely spared , and the main site of ablation is the periphery .
thus , in the absence of serious complications , such as decentered ablation or infection , there should be no significant haze formation or loss bcva.16 however , haze has been reported and can cause decreased corrected vision and regression after prk . without mmc , grades 1 and 2 haze ( hanna 's scale ) has been reported.7 in our study , with the use of mmc , there were just two cases of grade 2 peripheral haze which resolved by 12 months postoperatively .
high values of root mean square higher order aberrations in a 7 mm pupil size have been reported,16 which were largely due to coma and negative 4 order spherical aberration , especially with higher corrections .
we found hyperopic prk is an effective technique with good stability to correct low to moderate hyperopia , with some degrees of overcorrection during the first few months with regression toward emmetropia by 1-year .
safety , predictability , and stability are acceptable and comparable to that of hyperopic lasik after 1-year follow - up .
 purpose : to evaluate refractive and visual outcomes of photorefractive keratectomy with mitomycin - c . 
 ( prk - mmc ) for the treatment of mild to moderate hyperopia.materials and methods : this case series enrolled 21 patients with up to + 5.50 diopters ( d ) of hyperopia . 
 all 42 eyes were treated with the concerto ( wavelight ) or the technolas 217-z ( bausch and lomb ) excimer laser . 
 outcome measures included best corrected distance vision acuity ( bcva ) and uncorrected distance vision correction and refraction at 1 , 3 , 6 , and 12 months postoperatively.results:mean patient age was 44.8  11.3 years . 
 preoperatively , mean manifest refractive spherical equivalent ( mrse ) was + 2.00 d  0.76 d and mean spherical refractive error was + 2.57 d  0.87 d ( range , + 1.25 d to + 5.50 d ) . 
 at 12 months postoperatively , mean mrse was + 0.1 d  0.61 d. mrse was within  0.50 d of emmetropia in 29 eyes ( 69% ) , and 18 eyes ( 43% ) had 20/20 uncorrected distant visual acuity . 
 bcva increased by two lines or more in three eyes ( 7.1% ) and one line in two eyes ( 4.7% ) ; 31 eyes showed no change , three eyes ( 7.1% ) lost one line , and three other eyes ( 7.1% ) lost two lines of bcva . 
 no eyes lost more than two lines of bcva . 
 complications included grade 2 peripheral haze in two eyes which cleared by 12 months postoperatively.conclusion:prk-mmc was a safe and predictable method for the correction of mild to moderate hyperopia . 
INTRODUCTION
MATERIALS AND METHODS
RESULTS
DISCUSSION
CONCLUSION
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