The Study Of The Changes In Corneal Shape And The Optical Quality After Discontinuation In Orthokeratology

PurposeTo evaluate the changes of corneal shape and optical quality in myopia children after discontinuation in orthokeratology with the oculus pentacam and a double-pass instrument(OQAS-II).MethodsThis prospective study randomly recruited sixty myopia children(thirty-two females,twenty-eight males,right eye)aged from eight to sixteen wearing orthokeratology during October 2013 to March 2016 in Tianjin medical university eye hospital myopia clinic.Their spherical equivalent ranges from-0.75 to-5.50 diopters(-3.55± 1.78 D)and astigmatism is less than-1.50(-0.47±0.55 D).According to the degree of myopia,they are divided into three groups(-0.75D<SE?-2.00D for A,-2.00D<SE?-4.00D for Band-4.00D<SE?-6.00Dfor C).Each patient has to take examination with oculus pentacam three times under the same experienced practitioner in pre-treatment,one-year visit,one-week,one-month,three-month after discontinuation,collecting the parameters like corneal anterior and posterior curvature(flat k;steep k),anterior chamber depth(ACD)and central corneal thickness(CCT).In addition,we also get the values of MTF cut off frequency,Strehl ratio(SR)and Objective scattering index(OSI)by using an Optical Quality Analysis System(OQAS-II)with a 4 mm pupil in pre-treatment,one-year visit,one-week recovery visit and one-month recovery visit.The statistics analysis used SPSS 22.0(IBM,USA),corneal shape(curvature,thickness,ACD)and optical quality(MTF cutoff,SR,and OSI)before and after discontinuation of orthokeratology were compared using paired-samples t test,and P<0.05 has statistically significance.Results1.Compare to the pre-treatment,after one month discontinuation,low to middle myopia children(-0.75<SE<-4.00D)the corneal anterior curvature in group A(Flat K:pre-orthokeratology 41.98 ±1.09,one month later 41.87±1.09;Steep K:pre-orthokeratology 43.33 ±0.93,one month later 43.37± 1.01);in group B(Flat K:pre-orthokeratology 43.13 ± 0.92,one month later 42.91 ± 0.92;Steep K:pre-orthokeratology 44.23±0.92,one month later 44.11 ±0.92),there were no significant difference(P>0.05).Among high myopia children(-4.00D<SE?-6.00D),there were no significant difference between pre-treatment and three-month discontinuation in corneal anterior curvature(Flat K:pre-orthokeratology 42.24 ±1.43,three months later 42.14 ± 1.48;Steep K:pre-orthokeratology 43.70± 1.82,three months later 43.65 ± 1.75).There were no statistically significant changes in ACD and posterior curvature before and after orthokeratology.Central corneal thickness decreased after one year wearing,in group A(pre-orthokeratology 553.83± 19.93,one year later 546.83± 19.93);group B(pre-orthokeratology 553.00± 16.29,one year later 545.00± 15.29);group C(pre-orthokeratology 565.00±31.09,one year later 555.00±29.09),were statistically different(P<0.05).And there was no statistically significant difference between pre-treatment and three-month discontinuation,the CCT was 553.00±22.63?553.47± 16.34?563.29±31.08,respectively,P>0.05).2.Compare to the pre-treatment,MTF cut off decreased from(45.36±5.74)to(39.49±5.75),SR decreased from(0.27±0.07)to(0.21±0.05)and OSI increased from(0.38±0.20)to(0.61 ±0.25)in one-year visit(P<0.05).After one week discontinuation,MTF cut off and SR increased to(43.22±5.64)and(0.24 ± 0.06),respectively.OSI decreased to(0.42±0.06)(P<0.05).In one-month recovery visit,there were no significant differences in MTF cut off,SR and OSI).ConclusionThere are no significant difference of corneal posterior curvature and ACD between before and after orthokeratology.Compare to the pre-treatment,corneal anterior curvature(Flat k and Steep K)?SE and CCT decreased after one-year wearing.What's more,the time course of returning to the original corneal parameters vary among different degree of myopia.There is a decline in optical quality after wearing orthokeratology,insisting of the decrease of MTF cut off and SR,the increase of OSI and recover to the baseline in one-month discontinuation.