Highly Precise Corneal Surgery and All-Optical Histology with Femtosecond Lasers

We present an optimized femtosecond laser system for intrastromal tissue manipulation, application studies of commercial fs-LASIK procedures and results from the first successful demonstration of nonlinear (SHG) imaging of corneal ultrastrucrure and fs-induced morphology modification.

Optimal incision sites to reduce corneal aberration variations after small incision phacoemulsification cataract surgery

AIM： To analyze the effect of steep meridian small incision phacoemulsification cataract surgery on anterior,posterior and total corneal wavefront aberration.· METHODS： Steep meridian small incision phacoemulsification cataract surgery was performed in age-related cataract patients which were divided into three groups according to the incision site： 12 o＇clock, 9o＇clock and between 9 and 12 o＇clock（BENT） incision groups. The preoperative and 3-month postoperative root mean square（RMS） values of anterior, posterior and total corneal wavefront aberration including coma,spherical aberration, and total higher-order aberrations（HOAs）, were measured by Pentacam scheimpflug imaging. The mean preoperative and postoperative corneal wavefront aberrations were documented.·RESULTS： Total corneal aberration and total lower-order aberrations decreased significantly in three groups after operation. RMS value of total HOAs decreased significantly postoperatively in the 12 o＇clock incision group（P 〈0.001）. Corneal spherical aberration was statistically significantly lower after steep meridian small incision phacoemulsification cataract surgery in BENT incision group（P 〈0.05） and Pearson correlation analysisindicated that spherical aberration changes had no significant relationship with total astigmatism changes in all three corneal incision location.·CONCLUSION： Corneal incision of phacoemulsification cataract surgery can affect corneal wavefront aberration.The 12 o＇clock corneal incision eliminated more HOAs and the spherical aberrations decreased in BENT incision group obviously when we selected steep meridian small incision. Cataract lens replacement using wavefront-corrected intraocular lens combined with optimized corneal incision site would improve ocular aberration results.

Evaluation of preoperative dry eye in people undergoing corneal refractive surgery to correct myopia

AIM: To investigate the incidence of preoperative dry eye and related factors in patients undergoing corneal refractive surgery to correct myopia.METHODS: A total of 141 patients with myopia who underwent corneal refractive surgery were surveyed by questionnaires, tear film break-up time(BUT) test, Schimer I test(SIt), corneal fluorescein staining(FL) test and diagnosed according to the currently recognized domestic diagnostic criteria for dry eye. Correlation analysis of factors such as age, gender, regular wearing of contact lens(CL), diopter(spherical equivalent), corneal thickness, and corneal curvature that may affect the onset of dry eye was carried out to clarify the main influencing factors. RESULTS: There were 64 patients(45.39%) diagnosed with dry eye. The male patients(20.31%) was significantly less than that of non-dry eye subjects(41.56%;χ~2=7.260, P=0.007);the proportion of patients with dry eye wearing CL(81.25%) was significantly higher than that of non-dry eye subjects(51.95%;χ~2=13.234, P<0.001);the median diopter level of dry eye patients was-6.59(IQR:-8.87,-4.58) D, and the median diopter level of non-dry eye subjects was-5.69(IQR:-7.15,-4.03) D. The diopter level of dry eye patients was significantly higher(Z=-2.086, P=0.019). However, the age, best corrected visual acuity, and intraocular pressure of dry eye patients were not statistically different from those of non-dry eye subjects(t=-0.257,-0.383 and 0.778, P=0.798, 0.702, and 0.438);the corneal thickness and corneal curvature(K1 and K2) were also not statistically different either(Z=-1.487,-1.036 and-1.707, P=0.137, 0.300, and 0.088). The research further analyzes the three significant factors in the single factor analysis(gender, CL wear, and diopter) in a multi-factor way: CL wear and diopter were the influencing factors of dry eye disease. Among them, CL wear increased the risk of dry eye by 2.934 times compared with no CL wear;for every 1 D increase in diopter, the risk of dry eye increased by 0.761 times.CONCLUSION: Preoperative dry eye is relatively common in patients who undergo corneal refractive surgery to correct myopia, especially in patients who have a history of CL wear and a high diopter level before surgery. Therefore, it is necessary to carry out preoperative screening and timely treatment of dry eye to obtain the best treatment outcome and postoperative satisfaction.

Changes of lactate dehydrogenase in corneal edema after cataract surgery treated with trans-corneal oxygenation therapy

AIM:To investigate the changes in levels of the lactate dehydrogenase(LDH)enzyme in corneal edema after cataract surgery with trans-corneal oxygenation therapy.METHODS:This pre-post design study design conducted on 15 patients with corneal edema after cataract surgery and receiving trans-corneal oxygenation therapy.Tear sample(using Schirmer paper,from the inferior fornix of the conjunctiva)was carried out prior to trans-corneal oxygenation therapy,on the day 2(D2)and day 5(D5)postoperatively before and after trans-corneal oxygenation therapy.Visual acuity[VA(Log MAR)],corneal endothelial density,central corneal thickness(CCT),and coefficient of variation corneal endothelial(Co V)were recorded.The value of LDH was measured using ELISA.The difference in mean LDH value before and after trans-corneal oxygenation therapy,between two groups were analyzed using Wilcoxon signed rank test.RESULTS:There was a decrease in LDH tear concentration at D2(pre vs post:1127.54±497.09 vs 696.91±489.49;P=0.002)and D5(pre vs post:1064.17±677.77 vs 780.28±428.95;P=0.027)after trans-corneal oxygenation therapy as well as decrease in LDH concentration on the D2 compared to D5(P=0.041).The mean CCT was decreased significantly after the administration of trans-corneal oxygenation(pre vs post:632.10±25.66 vs 563.90±51.54;P=0.005).The mean VA and Co V increased significantly after the administration of trans-corneal oxygenation(P=0.001 and P=0.028,respectively).However,there was no difference in mean of corneal endothelial density(P=0.814).CONCLUSION:Trans-corneal oxygenation therapy is associated with significant decrease of tears LDH levels in post cataract surgery with corneal edema.It is accompanied by clinical improvement such as significant reduction of CCT.

Short term effects of small incision lenticule extraction surgery on corneal endothelium

AIM： To assess the effects of small incision lenticule extraction（SMILE） surgery on the corneal endothelium at1 d to 1mo postoperatively.·METHODS： A retrospective, observational study was conducted on 47 patients（47 eyes） who received SMILE surgery. Patients were grouped according to contact lens wear condition. The corneal endothelium was examined preoperatively and at 1d, 1wk and 1mo postoperatively.The corneal endothelium was analyzed for endothelial cell density（ECD）, percentage of hexagonal cells, and coefficient of variation（CV） of cell size.·RESULTS： There were no significant decrease in the ECD, percentage of hexagonal cells or increase in CV at1 d, 1wk and 1mo postoperatively（P 〉0.05）. However,there was a small increase of ECD by 2.88% in contact lens wearers（78.26±113.62 cell/mm2, P 〈0.05）.· CONCLUSION： SMILE has no significant adverse effects on the corneal ECD and morphology during 1mo follow-up time.

A 3-month comparison study of subjective and objective visual quality of small incision lenticule extraction and transepithelial photorefractive keratectomy in patients with low and moderate myopia

AIM:To compare the subjective and objective visual quality between small incision lenticule extraction(SMILE)and transepithelial photorefractive keratectomy(t PRK)in patients with low and moderate myopia.METHODS:Patients undertaking SMILE or t PRK for the correction of low and moderate myopia were consecutively recruited in this prospective cohort study with a 3-month follow-up period.Objective evaluation[visual acuity test,manifest refraction,wavefront aberrations,the total cut-off value of the total modulation transfer function(MTFcut-off),and Strehl ratio(SR)]and subjective evaluation of visual quality(quality-of-life questionnaire)were conducted before surgery and at days 1,7,30,and 90 after surgery.RESULTS:A total of 47 patients(94 eyes)with SMILE and 22 patients(22 eyes)with t PRK were enrolled.The uncorrected visual acuity(UCVA)was better in SMILE patients on day 7 after surgery(1.13±0.13 vs 0.99±0.17,t=4.85,P<0.001)but was comparable at days 30 and 90.At day 90,the SMILE group had a lower spherical equivalent(SE)than the t PRK group(0.04±0.31 vs 0.19±0.43,t=2.08,P=0.042).Total higher order aberrations(HOAs)were induced in both surgical types,which were more evident in the t PRK group with 3-mm pupil diameter(0.16±0.07 vs0.11±0.05,t=4.27,P<0.001)and 5-mm pupil diameter(0.39±0.17 vs 0.36±0.11,t=2.33,P=0.022).The MTFcut-offand SR showed a trend of improvement in both SMILE and t PRK patients but were statistically better in the SMILE group with both pupil diameters.There was a significant improvement of contrast sensitivity(CS)over baseline levels at the spatial frequency of 18 cycles/degree(c/d)in the SMILE group(F=2.72,P=0.033)and at 3 c/d(F=3.03,P=0.031),12 c/d(F=3.72,P=0.013),and 18 c/d(F=4.62,P=0.004)in the t PRK group.The subjective quality of life questionnaire showed a steady improvement in the SMILE group(F=8.31,P<0.001)but not the t PRK group.CONCLUSION:SMILE and t PRK are both safe and effective ways to correct low and moderate myopia.A generally better and quicker recovery of visual quality favors the application of SMILE in qualified patients.

Intraocular lens power calculation in eyes with previous corneal refractive surgery

Background:This review aims to explain the reasons why intraocular lens(IOL)power calculation is challenging in eyes with previous corneal refractive surgery and what solutions are currently available to obtain more accurate results.Review:After IOL implantation in eyes with previous LASIK,PRK or RK,a refractive surprise can occur because (i)the altered ratio between the anterior and posterior corneal surface makes the keratometric index invalid;(ii)the corneal curvature radius is measured out of the optical zone;and (iii)the effective lens position is erroneously predicted if such a prediction is based on the post-refractive surgery corneal curvature.Different methods are currently available to obtain the best refractive outcomes in these eyes,even when the perioperative data(i.e.preoperative corneal power and surgically induced refractive change)are not known.In this review,we describe the most accurate methods based on our clinical studies.Conclusions:IOL power calculation after myopic corneal refractive surgery can be calculated with a variety of methods that lead to relatively accurate outcomes,with 60 to 70%of eyes showing a prediction error within 0.50 diopters.

The evolution of corneal and refractive surgery with the femtosecond laser

The use of femtosecond lasers has created an evolution in modern corneal and refractive surgery.With accuracy,safety,and repeatability,eye surgeons can utilize the femtosecond laser in almost all anterior refractive procedures;laser in situ keratomileusis(LASIK),small incision lenticule extraction(SMILE),penetrating keratoplasty(PKP),insertion of intracorneal ring segments,anterior and posterior lamellar keratoplasty(Deep anterior lamellar keratoplasty(DALK)and Descemet's stripping endothelial keratoplasty(DSEK)),insertion of corneal inlays and cataract surgery.As the technology matures,it will push surgical limits and open new avenues for ophthalmic intervention in areas not yet explored.As we witness the transition from femto-LASIK to femto-cataract surgery it becomes obvious that this innovation is here to stay.This article presents some of the most relevant advances of femtosecond lasers to modern corneal and refractive surgery.