Changes in corneal biomechanics and intraocular pressure following Femto-LASIK using Goldman applanation tonometry and ocular response analyzer

AIM:To compare intraocular pressure(IOP)measurements before and after laser in situ keratomileusis(LASIK)with a femtosecond laser for flap creation using ocular response analyzer(ORA)and Goldmann applanation tonometry,and to identify factors that may influence the preoperative and postoperative IOP.METHODS:A prospective study conducted on myopic patients who underwent LASIK using a femtosecond laser for flap fashioning.Enrolled patients were evaluated preoperatively,6 wk and 3 mo postoperatively for manifest refraction(MR),keratometric(K)readings and central corneal thickness(CCT)using a scheimpflug-based topography.Corneal resistance factor(CRF),corneal hysteresis(CH),Goldmann correlated IOP(IOPg)and corneal compensated IOP(IOPcc)were measured using ORA besides IOP assessment by Goldman applanation tonometry(GAT).RESULTS:There was a statistically significant decrease in measures of IOPg by 3.35±0.83 mm Hg,followed by GAT which decreased by 2.2±0.44 mm Hg,and the least affected by operation was IOPcc which decreased only by 0.87±0.1 mm Hg after 6 wk.After 3 mo follow up there was a statistically significant decrease in IOPcc which decreased only by 0.76±0.4 mm Hg,followed by IOP GAT by 1.6±0.5 mm Hg,and the most affected by operation was IOPg which decreased by 2.3±0.3 mm Hg.Correspondingly,there was a statistically significant decrease in CH and CRF after 6 wk and 3 mo.At 3 mo,the preoperative MR and preoperative GAT were prominent significant predictors of the postoperative GAT changes.The prediction equation was subsumed.CONCLUSION:IOP measurements and corneal biomechanical factors reduce significantly after LASIK with a femtosecond laser for flap creation.The IOPcc values are less influenced by changes in corneal properties than IOPg and GAT,indicating that IOPcc may provide the most reliable measurement of IOP after this procedure.

Two-stage procedure in the management of selected cases of keratoconus: clear lens extraction with aspherical IOL implantation followed by WFG-PRK

AIM： To assess the objective and subjective results of a two-stage procedure for management of keratoconus： clear lensectomy with aspherical intraocular lens（IOL） implantation followed by wave front-guided photorefractive keratotomy（WFG-PRK）.METHODS： This prospective interventional non-randomized study included patients aged 35 years old or more with grade I and II stable keratoconus, a clear visual axis, minimal corneal thickness（MCT） 420 μm or more and average keratometric reading（K） less than 54 diopter（D）. Refraction of all selected eyes should be-8.00 D sphere or more with less than-6.00 D cylinder and could be corrected two lines or more with spectacles or contact lenses. All studied eyes underwent a two-stage approach treatment： first refractive lens exchange and aspherical IOL implantation followed, after at least 3 mo, by WFGPRK. Pre and postoperative complete ophthalmological examination were performed. Topographical, visual and aberrometric results were recorded and evaluated during 6 mo follow up period. Moreover, patient satisfaction and other subjective outcomes were also analyzed.RESULTS： The 13 eyes of 11 patients diagnosed with stable keratoconus and aged from 39 to 49 y（42.4±6.2 y） were enrolled in the study. At baseline, 8 eyes had grade I and 5 eyes had grade II keratoconus. The manifest sphere was-10.3±4.2 D（ranged from-8.0 to-14.0 D） and the manifest cylinder was-4.2±1.2 D（ranged from-1.75 to-5.50 D）. After the two-stage procedure, sphere and cylinder reduced significantly to-0.43±0.22 D and-1.3±0.72 D respectively（P〈0.001）. There was also a highly significant improvement in the mean uncorrected distance visual acuity（UDVA） from logMAR 1.41±0.49 preoperatively to 0.51±0.16 postoperatively（P〈0.001） and the mean corrected distance visual acuity（CDVA） from 0.76±0.24 preoperatively to 0.49±0.13 after the operation（P〈0.001）. All aberrometric and mesopic vision parameters and most of the topographical indices demonstrated highly significant improvement that remains stable until the end of follow up. All recorded subjective data revealed a high degree of patient satisfaction.CONCLUSION： Two-stage approach（clear lens exchange with monofocal IOL followed by WFG-PRK） in selected cases of keratoconus is a safe, effective and highly predictable procedure with satisfactory visual and refractive results.