Dry Eye After Corneal Refractive Surgery Confocal Microscope

ObjectiveTo observe the regeneration of subbasal epithelial nerve plexus in central cornea after LASIK surgery, and study the correlation between its measurements and dry eye test values, so as to promote our knowledge about the pathophysiological mechanism of post-LASIK dry eye and optimize its therapeutic options.MethodsForty-two myopic patients (84eyes) who had conventional LASIK/femtosecond-assisted LASIK from October2011to September2012in PUMCH were included in this cross-sectional study. Patients were divided into two groups (six-month group and one-year group) based on the post-LASIK follow-up period. Subjective and objective dry eye tests were carried out to determine patients’ degree of post-LASIK dry eye, and confocal microscopy was used to observe the regeneration of subbasal epithelial nerve plexus that could then be analyzed by ACCMetrics software using quantitative parameters, such as the density, length, tortuosity and width of corneal nerve fiber. The quantitative data of the two groups was compared using an independent sample t test, and the correlation among dry eye test values, nerve fiber measurements, depth of excimer laser ablation and thickness of residual stromal bed was assessed by partial or bivariate correlation method.Results1. The values of Schirmer test and TBUT were higher and the score of fluorescein staining was lower in patients from the one-year group when compared with those from the six-month group (t=-2.340,-5.403,2.634, P<0.05), but there was no statistically significant difference in the OSDI score between the two groups (t=1.207, P>0.05). In terms of nerve fiber measurements, the values of CNFD, CNBD, CNFL and CTBN in patients from the one-year group were all higher than those from the six-month group (t=-3.293,-4.501,-7.091,-4.240, P<0.01), but there was no statistically significant difference in the values of CNFW and CNFT between the two groups (t=1.480,0.474, P>0.05).2. For patients in the six-month group, the value of CNBD was negatively correlated with the score of fluorescein staining (r=-0.346, P<0.05), while none of the other nerve fiber measurements was correlated with any of the dry eye test values (P>0.05). However, for patients in the one-year group, the value of Schirmer test was positively correlated with that of CNFD (r=0.321, P<0.05), but negatively correlated with that of CNBD, CTBN, and CNFT respectively (r=-0.347,-0.340,-0.325, P<0.05), and the value of CNFW was positively correlated with the score of OSDI (r=0.342, P<0.05), while none of the other nerve fiber measurements was correlated with any of the dry eye test values (P>0.05).3. There was no statistically significant difference in either dry eye test values or nerve fiber measurements between patients who had conventional LASIK surgery and those who had femtosecond-assisted LASIK surgery (P>0.05).4. For patients in the six-month group, none of their nerve fiber measurements or dry eye test values was correlated with either the depth of excimer laser ablation or the thickness of residual stromal bed (P>0.05). However, for patients in the one-year group, the value of TBUT was negatively correlated with the depth of excimer laser ablation (r=-0.297, P<0.05), while none of the other nerve fiber measurements or dry eye test values was correlated with either the depth of excimer laser ablation or the thickness of residual stromal bed (P>0.05). Conclusions1. For patients who are one-year post-LASIK, their values of objective dry eye testsare greatly improved, and the density and length of their subbasal epithelial nerve plexus in central cornea are significantly increased when compared with those of patients who are six-month post-LASIK.2. Some measurements of subbasal epithelial nerve plexus in central cornea arecorrelated with some of the dry eye test values, which are more common in one-year post-LASIK patients.3. The difference between conventional-LASIK and femtosecond-assisted LASIKdoes not significantly affect the dry eye test values and nerve fiber measurements in patients who are six-month or one-year post-LASIK.4. The TBUT value of one-year post-LASIK patients is negatively correlated withthe depth of excimer laser ablation.