We retrospectively reviewed all the electronic medical records of patients who had received phacoemulsification cataract surgery by Chen HC with intraocular lens implantation at Chang Gung Memorial Hospital, Linkou from January 1st, 2016 to December 31th, 2017. Information on demographics, past systemic and ocular history, slit lamp examination, fundus examination, preoperative corrected distance visual acuity (CDVA) and IOP, VA and IOP in postoperative 3 days, 10 days, 1 month, and 3 months were collected. IOP measurement was performed by a non-contact tonometer (NT-530P, Nidek, Aichi, Japan). Surgical details including methods for sealing the wound, operation time, and intraoperative complications were documented. Phacoemulsification time and cumulative dissipated energy (CDE) were recorded from Infinity Vision System (Infinity, Alcon, Texas, USA). To investigate the effect of air bubble to corneal endothelium, endothelial cell density (ECD), coefficient of variation (CV) in cell size, percentage of hexagonal cells (HEX), and central corneal thickness (CCT) were evaluated preoperatively and 1-month post-operatively in some patients by a non-contact in vivo specular microscope (CEM-530, Nidek, Gamagori, Japan).
The exclusion criteria were as follows: (1) intraoperative complications including posterior capsule rupture, intraocular lens (IOL) placed in sulcus, vitreous loss, lens drop, zonular dialysis, iridodialysis, etc.; (2) previous ocular trauma or intraocular operation; (3) presence of ocular disease or ocular history that may affect VA or IOP such as vitreoretinal disease, glaucoma, ocular surface disease, corneal dystrophy, optic neuropathy, amblyopia, etc.; (4) follow-up less than 1 month after the surgery; (5) poor general condition or consciousness that VA or IOP could not be measured accurately.
All cataract surgery was performed by one well-experienced surgeons (Dr. Chen HC) using the standard divide and conquer technique and the same phacoemulsification equipment (Infinity Vision System) at similar settings. Preoperative medications included 1 drop of 1% cyclopentolate, and 1 drop of 10% phenylephrine 20 minutes before surgery. Standardized surgical technique was performed including the use of a sterile drape with speculum, topical 2% lidocaine hydrochloride and 1:5000 adrenaline, creating a 2-plane CCI with a 2.65 mm slit blade, injection of viscoelastic agents (DuoVisc; Alcon, Texas, USA), creating a continuous circular capsulorrhexis with capsulorrhexis forceps only, application of hydrodissection with balanced salt solution (BSS), phacoemulsification with OZil® Intelligent Phaco handpiece and traditional divide and conquer technique, irrigation and aspiration of the cortical material with I/A probe, introduction of viscoelastic agents in bag, implantation of one-piece foldable acrylic IOL in the bag with injector, and aspiration of the residual viscoelastic agents. Closure of the incision wound was done by stromal hydration using a 30-gauge cannula with no sutures, or sutured with 10 − 0 nylon if indicated, from January 2016 to November 2016. Since December 2016, Dr. Chen HC started to seal the wound with IABT as follows (1) draw room air without using filter with a 5mL syringe, (2) inject room air into AC with a 30-gauge cannula until the diameter of air bubble reaches 80% of the corneal diameter (Fig. 1-A), (3) check IOP with palpation, (4) adjust the size of air bubble by injecting or leaking more room air to optimize IOP, (5) check wound leakage by observing the size of air bubble directly. Patients were divided into IABT group and non-IABT group according to the method of wound closure.
Standardized postoperative medications were topical 0.3% Tobramycin + 0.1% Dexamethasone suspension 4 times per day for two week and then shifted to 0.25% chloramphenicol + 0.1% fluorometholone 4 times per day for two weeks. Patients were scheduled to return to clinic 1 day, 3 days, 10 days, 1 month, and 3 months after the surgery. Postoperative complications including pupillary block, endophthalmitis, prolonged corneal edema, ocular hypertension, cystoid macular edema, retinal detachment, or other surgery-related complications were documented. Prolonged corneal edema was defined as corneal edema noted 10 days after the surgery. Ocular hypertension was defined as IOP over 25mmHg that required transient topical antiglaucoma agents.
Continuous variables were compared using two-tailed independent t test. Large and small sample categorical variables were compared using Chi-squared test and Fisher’s exact test. Generalized estimating equations (GEE) model was employed to analyze VA, CDVA and IOP during follow-up period. The linking function was identity and distribution was normal in the GEE. First order auto-regressive working correlation and robust standard error were adopted to obtain the significance of parameters. Repeated measures analysis of variance (ANOVA) was used to compare pre- and post-operative endothelial characteristics between IABT and non-IABT group. Age, operation time, phacoemulsification time and CDE were used as covariates in both GEE and repeated measures ANOVA analysis. All statistical analyses were conducted using SPSS version 19.0 for Windows (IBM, Armonk, New York, USA). P value < 0.05 denotes statistically significant difference.
This study was approved by the institutional review board of Chang Gung Medical Foundation (IRB No: 201901793B0), and the waivers of informed consent were also approved for retrospective, secondary analysis of existing data. This study adhered to the tenets of the Declaration of Helsinki. The author declared no conflict of interest.