الفهرس 
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Abstract
Cataract is considered the leading cause of reversible blindness worldwide, Nowadays cataract extraction surgery by phacoemulsification is one of the most common surgical procedures done on a global scale.
The use of OVDs has become so essential and important in modern cataract surgery by phacoemulsification to perform safer surgery and for better and faster visual recovery for the patients.
OVDs play many roles by their different composition and physical properties; in general they are important in coating and protecting delicate intraocular structures especially the corneal endothelium, maintaining the anterior chamber depth and preventing its collapse during capsulorrhexis, filling the capsular bag during the implantation of the intraocular lens.
Also in case of complications as posterior capsular tear it is important in tamponading the vitreous and preventing further vitreous prolapse in the anterior chamber.
OVDs come in two major classes, Dispersive viscoelastics with lower molecular weight and lower surface tension with better ability to coat and protect, and Cohesive viscoelastics with higher molecular weight and higher surface tension with better ability to maintain space and pressure.
Specular microscopy is a noninvasive photographic technique that allows visualization and analysis of the corneal endothelium. Using computer assisted morphometry, modern specular microscopes analyze the size, shape and population of the endothelial cells.
The instrument projects light onto the cornea and captures the image that is reflected from the optical interface between the corneal endothelium and the aqueous humor. The reflected image is analyzed by the instrument and displayed as a specular photomicrograph.
In our study we compared the effect of different concentrations of methyl cellulose (2% and 2.4%) on the corneal endothelium during phacoemulsification.
The patients were assigned to two groups, complete ophthalmic examination and specular microscopy were done pre-operatively and one month post-operatively to detect the change in corneal endothelium and the effect of different concentrations of methyl cellulose.
The endothelial cell loss was significant between the 2 groups, in group 1 it was 362.267 ± 52.020 (14.515 % ± 1.458) and in group 2 it was 335.667 ± 21.170 (13.494% ±0.667).So these results shows that HPMC 2.4% gives better protection than HPMC 2% on corneal endothelium during phacoemulsification on terms of the postoperative endothelial cell count and the endothelial loss after phacoemulsification.
The study results also showed postoperative significant improvement in best corrected visual acuity and significant reduction on intraocular pressure in both study groups, but the results were comparable in both groups with no effect on the clinical outcomes in patients.
To summarize both concentrations of methyl cellulose (2% and 2.4%) can be used during phacoemulsification as both concentrations are able to protect the corneal endothelium and to perform the surgery with high safety profile, and to decrease the incidence of intraoperative complications which leads to fast postoperative visual recovery for the patient and the ability to perform daily life activities in a normal way. However, methyl cellulose 2.4% gives better protection, so it is better to be used in patients with borderline endothelial count and in conditions of expected intraoperative endothelial cell loss as hard cataracts and pseudo-exfoliation syndrome.