Corneal Topographic Changes after Subscleral Trabeculectomy

INTRODUCTION

Intraocular pressure (IOP) is the major risk factor of glaucoma and existing glaucoma therapies are exclusively aimed at lowering IOP. In one large population cohort, 1 in 6 people with OAG(open angle glaucoma) became bilaterally blind.¹

The only proven way to prevent vision loss is to reduce the pressure inside the eye (intraocular pressure) over the long term. Approaches to reducing intraocular pressure (IOP) include medical therapy, laser treatments, and surgery. As commercially available eye drop preparations have a short-lasting effect, medical therapy requires eye drops to be instilled one or more times daily for life. Trabeculectomy marked a major advance in glaucoma surgery.²

Trabeculectomy remains the standard surgical procedure for glaucoma when medical and laser treatments fail to control intraocular pressure (IOP).

This involved the removal of a partial                      thickness block of limbal tissue containing trabecular meshwork, sclera, and cornea under a lamellar scleral flap. Closure of the scleral flap controlled the egress of aqueous humor and reduced the major early postoperative complications.³

The change in astigmatism after trabeculectomy can lead to a decrease in the visual acuity in some patients and it would be useful to know when refraction stabilize. Over the last few years several studies have suggested that early trabeculectomy may be superior to medical therapy in the treatment of primary open angle glaucoma.⁴

Topographic assessment of corneal changes after trabeculectomy showed that the majority of the post-operative changes are found in the superior semimeridian.⁵

It was stated that the trabeculectomy operation induces changes in corneal keratometry, astigmatism and topography that results in visual acuity decline as well as corneal aberrations influences the visual function such as reading and driving, especially at night that affect the quality of life.⁶

Hence, assessment of corneal topography following trabeculectomy in order to investigate the changes of these factors. The results might be helpful in postsurgical management of patients with open angle glaucoma particularly in early stages following trabeculectomy.

The aim of the study is to investigate the effect of trabeculectomy on corneal topography, anterior chamber depth, and aberrations by a SIRIUS topography.

PATIENTS AND METHODS

Ethical Statement:

A written informed consent was obtained from each eligible patients prior to study’s enrollment. The study’s protocol was reviewed and approved by ethics committee or audit department of ophthalmology department, Faculty of Medicine, Al Azhar University.

Study Design and Setting:

The present study was a prospective cohort study including 30eyes of patients who were scheduled to undergo trabeculectomy at Ophthalmology Department of Al Azhar university hospital during the period from January 2018 to August 2019.

Sample Size and Sampling:

The predetermined sample size was 30eyes. We used non-probability consecutive sampling technique to collect the data from eligible patients; the patients were recruited consecutively from Ophthalmology Department of Al Azhar university hospital.

Preoperative Assessment:

In the present study, all eligible patients were subjected to: Details history of previous of systemic or ocular diseases / surgery, Complete ophthalmological examination, including: (Best corrected visual acuity (BCVA(, Slit-lamp examination, Fundus examination with optic disc evaluation, Intraocular pressure recording (using the Goldmann’sapplanation tonometry and Measurement of Corneal k reading, coma, high order and spherical abberations and anterior chamber depth were taken by SIRIUSTopographer® (CSO, Firenze, Italy). Itis a Scheimpflug‐Placido device integrating a Placido topographer with a dual and single rotating Scheimpflug camera, respectively.The Sirius provides measurements of ACD, anterior chamber volume (ACV),central corneal thickness(CCT), pupil size, corneal volume,keratometry and abberations.⁷

Steps of the Operation:

Preoperatively, patient’s IOP was controlled medically by ocular hypotensive agents. If not controlled, a general anaesthetic was recommended.Eyelashes were kept away off the field by a guarded speculum or sticky drape In addition, patients underwent routine preoperative laboratory investigations including complete blood profile, blood glucose profile, and cardiac investigations.

Intraoperatively, local anaestheticwas used in the form ofperibulbar lignocaine 2% .

Then, a superior corneal traction suture was done followed by fornix-based incisions.The Tenon'swas attached about 0.5 mm behind the conjunctiva at the limbus. A cytotoxic agent (mitomycin C) was applied. This step was followed by focal cauterization of vessels.

Fig. 1: Traction suture.

Fig. 2: Conjunctival incision

Square 4x4 scleral flap was used, followed by straight dissection of the flap at the base, right where dissection was occurring. An infero-temporally placed paracentesis was then placed to allow anterior chamber access both at surgery and post-operatively. Sclerostomy was performed by direct, half-thickness cuts.

Fig.3: Cutarizations of bleeding vessels.

Fig.4: Sclera flap and dissection of the flap.

This step was followed by peripheral iridectomy peripherally and parallel to the limbus. Sutures to sclera were done by prolen 10/0 and conjunctival sutures were done.

Fig. 5:Trabeculectomy.

Fig. 6: Conjunctival sutures were done.

Finally subconjunctival injection of appropriate steroid and antibiotic was done.

Postoperative Follow-up:

Patients were follow-up at day 1, week 1, and 1st month after the surgery to record the following parameters: IOP using a calibrated applanation tonometer, Number of IOP lowering medications if required and Measurement of Corneal k reading, corneal abberations and anterior chamber depth by SIRIUS after subscleraltrabeculectomy surgery at 1 month follow up visit.

Statistical Analysis:

An Excel spreadsheet was established for the entry of data. We used validation checks on numerical variables and option-based data entry method for categorical variables to reduce potential errors. The analyses were carried with SPSS software (Statistical Package for the Social Sciences, version 24, SSPS Inc, Chicago, IL, USA). The normality of the data were assessed using Shapiro-Wilk Test. Numerical data were described as mean ±SD if normally distributed; or median and interquartile range [IQR] if not normally distributed. Frequency tables with percentages were used for categorical variables. Independent Student t-test and paired t-test were used to compare parametric quantitative variables; while Mann-Whitney tests and Wilcoxon matched pairs test were used to compare non-parametric quantitative variables. Chi-square test or McNemar-Bowker tests were used to analyze categorical variables. A p-value < 0.05 is considered statistically significant.

RESULTS

The present study was a prospective cohort study including 30 eyes of patients who were scheduled to undergo trabeculectomy at Ophthalmology Department of Al Azhar university hospital during the period from January 2018 to August 2019.

* Data are presented as mean ±SD, median (Range), or number  (%)

Table 1:Thedemographic characteristics of the included patients.

The age of the included patients ranged from 26-72 years old with a mean age of 47.13 ±13.7years old. Fourteen (46.7%) patients had diabetes, 53.3% had hypertension, and 20% had history of cardiac diseases.

* Data are presented as mean ±SD and median (range(

Table 2: Preoperative Keratometry and Biometry Findings.

Preoperatively, the mean IOP was 23.87 ±1.3mmHg and the mean best corrected visual acuity was 0.313 ±0.12.

 *Data are presented as mean ±SD and median (range(

Table 3: Preoperative Aberrations Findings.

Preoperatively, the mean high order aberration was 0.467 ±0.23 and the mean coma aberration was 0.268 ±0.17. The mean astigmatism was1.1 ±0.36.

* Data are presented as mean ±SD, median (Range). T Using paired-t-test.

Table 4: The changes in IOP and BCVA among the included patients.

There were statistically significant differences between pre and postoperative values of IOP (p <0.001) and BCVA (p < 0.001). Eyes showed statistically significant reductions in IOP and increase in BCVA.

*Data are presented as mean ±SD and median (range).^TUsingpaired-t-test. ^KUsingKruskal-Wallis test

Table 5: The Changes in Keratometry and Biometry Findings of the included patients

There were statistically significant differences between pre and postoperative values ofK1 (p =0.019), astigmatism (p =0.033), and ACD (p <0.001). Eyes showed statistically significant increase in K1, astigmatism values, and decrease in ACD. In contrary, there was no statistically significant difference between pre and postoperative values of K2 (p =0.2).

*Data are presented as mean ±SD and median (range).^KUsing Kruskal-Wallis test

Table 6: The changes in Aberrations Findings of the included patients

There were statistically significant differences between pre and postoperative values of high order aberration (p <0.001), coma aberration, and spherical aberration (p <0.001). Eyes showed statistically significant increase in the three parameters.

*Data are presented as mean ±SD and median (range). ^wUsing Mann-Whitney test

Table 7: The association between studied groups and preoperative Keratometry and Biometry Findings

*Data are presented as mean ±SD and median (range). ^wUsing Mann-Whitney test

Table 8: The association between studied groups and postoperative Keratometry and Biometry Findings.