A comparative study of corneal topographical and central corneal thickness changes in diabetics and non-diabetics before and after phacoemulsification: A study protocol

Introduction

Diabetes mellitus is a metabolic disorder causing elevated blood glucose levels in the blood.¹ Diabetes mellitus is a global concern and has several effects systemically.²

Ocular manifestations of diabetes include refractive changes, dry eye, extraocular muscle plasy, diplopia, diabetic macular edema, diabetic retinopathy and ischemic optic neuropathy.³ Corneal complications caused by diabetes include delay in wound healing, loss of sensitivity of cornea, recurrent erosions and changes in tear film.⁴ Diabetes mellitus affects metabolic, clinical, morphological, metabolic and physiological state of the cornea.⁵ Transient changes in the refraction can occur due to acute hyperglycemia.⁶ Several studies concluded that evidence of increased central corneal thickness, and decreased endothelial cell density,change in the size and shape of the endothelial cells is seen in diabetic cornea.³

Hyperglycemia causes overexpression of inflammatory mediators and proinflammatory proteins and plays a role in the development of diabetic keratopathy.⁷ Diabetic corneal neuropathy is caused due to damage to trigeminal nerve caused due to chronic hyperglycemia.⁸ Advanced glycation end products and Matrix metalloproteinases cause damage to the cornea by apoptosis of endothelial cells of cornea.⁹ Central corneal thickness changes in the cornea of the diabetic patients is caused due to metabolic stress affecting corneal hydration due to increase in the endothelial permeability.¹⁰ High glucose levels reduce the activity of Na-K+ ATPase which is the major component of endothelial cells causing morphological changes in the permeability of diabetic corneas. The development of changes also depends on the duration diabetes and the degree of metabolic dysregulation.¹¹

The global diabetic population at present is 537 million. According to the international diabetes federation diabetes is expected to increase to 643 million by 2030.¹²

Specular microscopy is a diagnostic tool which is non-invasive and helps in the evaluation of corneal endothelium and central corneal thickness. This shows a distinctive pattern in different endothelial diseases.¹³

Corneal topography is a non-invasive diagnostic tool used to assess corneal curvature and astigmatism. It works by projection of rings of light onto the cornea and capturing their image to generate a topographic image.¹⁴

Protocol

Methods

This is a hospital based study where it is conducted in the Department of Ophthalmology at AVBRH, Sawangi after approval from the ethics committee of the institute. Patients admitted for the cataract extraction by phacoemulsification will be taken for the study where comprehensive ophthalmic examination, Visual acuity will be measured using Snellen chart where patient is made to sit at a distance of 6 meters from the chart. Then, one eye is covered with the hand and the patient is made to read the chart until they can no longer identify the majority of characters in that row. Then the result is recorded and the same is done for the other eye, and the results are interpreted. Slit lamp examination is done, where patient is made comfortably seated in the examination chair and the light of the slit lamp, light intensity and magnification are adjusted. The patient is positioned with their forehead and chin in place to keep the head steady, and the slit beam is adjusted. The examination of anterior segment is done. Fundus ophthalmoscopy is done by indirect ophthalmoscopy using 20D lens and fundus findings are noted. Intraocular pressure measurement by applanation tonometer will be carried out, where the patient is comfortably seated and topical anesthesia is applied to both eyes to minimize discomfort. The tonometer tip is placed on the cornea and gentle pressure applied, and the cornea is flattened while intraocular pressure measurements are taken. IOL power calculation using the SRK-T formula will be measured, where corneal curvature measurements are taken using corneal topography and axial length is measured using ultrasound biometry (A-scan), and anterior chamber depth is taken into account. The SRK/T formula is: IOL power (P)=A-constant(A) – (2.5×AL) + (0.9×K). Random blood sugar levels measured by glucometer will be taken into consideration, preoperative central corneal thickness by Topcon SP-IP specular microscope and corneal topography using Orbscan corneal topography system are recorded, detailed past history and history of systemic illness will be taken.

Study participants will be divided into two groups where people having Diabetes mellitus type 2 will be taken in group A and people having no history of diabetes will be taken in group B. All the patients are allotted in the groups after taking inclusion and exclusion criteria into consideration. Informed written consent will be taken from all the patients. Both study groups will undergo phacoemulsification surgery following standard surgical protocols. Corneal topographical and central corneal thickness changes will be recorded postoperatively after one week, one month and three months follow up. Statistical analysis will be conducted between the two groups to compare preoperative and postoperative central corneal thickness and corneal topography before and after phacoemulsification surgery.

Both the diabetic and non-diabetic groups will undergo phacoemulsification surgery.

Phacoemulsification is a modern day cataract surgery. All the aseptic precautions like hand hygiene and use of sterile gloves and instruments to reduce risk of contamination will be taken and peribulbar anaesthesia is given to the operating eye and eye is draped and painted with betadine and globe exposure is done with eye speculum and sideport incision is taken with 15degree blade and continuous curvilinear capsulorrhexis of anterior capsule is performed with cystitome and clear corneal incision of 2.8mm wide is taken. Hydrodissection is performed using to separate the cortex from posterior capsule which helps in nucleus rotation and also facilitate to perform trenching as nucleus is prolapsed anteriorly and viscoelastic is introduced into anterior chamber before phacoemulsification which prevents corneal endothelial damage. Ultrasound energy is used to break the nucleus into fragments and then vacuum is used to catch the nuclear material and irrigation and aspiration for cortex removal and viscoelastic removal. Intraocular lens implantation is done under viscoelastic cover after extension of clear corneal incision in case of rigid intraocular lens implantation. Then the viscoelastic material is washed using Simcoe cannula and anterior chamber is formed and wound is closed.

Selection bias can occur while conducting the study. To prevent selection bias, patients who have had diabetes for at least of 5 years will be taken into the study.

Confidentiality of the study participants will be maintained by not revealing the identity of the patient like name and address and by using the admission code for identification. Raw data will be available only to the authorised individuals.

Outcomes

Discussion

In our study we are expecting differences in the corneal topography and central corneal thickness changes in diabetics preoperatively and postoperatively changes are seen in both the groups however we expect diabetic patients show prolonged corneal healing as compared to non-diabetics and diabetics are expected to show increased central corneal thickness following phacoemulsification.

Xiao-yang Luo et al., conducted a study which showed that diabetes and hyperglycemia are associated with greater central corneal thickness.¹⁶

Nagaraj et al., showed that endothelial cell density was decreased and central corneal thickness was increased in diabetics than non-diabetics.¹⁷

Sonmez et al., evaluated corneal topographic measurements in patients of acute severe hyperglycemia and concluded that eyes in diabetic patients displayed higher keratometric readings than eyes of nondiabetic ones.¹⁸

Busted et al., no correlation was found between diabetes duration, blood sugar levels, and use of insulin and central corneal thickness.¹⁹

Artur Jose Schmitt et al., showed that there is no significant change in the posterior corneal cuvature after phacoemulsification.²⁰