The corneal epithelium is the outermost layer that covers the front of the eye; it not only functions as a barrier that blocks the passage of foreign material, but also plays an important role in maintaining high optical quality. The stem cells in the basal layer of the limbal epithelium hold a physiological significance in the renewal and metabolism of corneal epithelium, particularly under stressful situations.

The cornea in diabetic patients suffers from cellular dysfunction and dysfunctional repairal mechanisms, which include recurrent erosions, delayed wound healing, ulcers, and edema. In addition and undoubtedly related to epithelial dysfunction, alterations in epithelial basement membrane occur.

Inclusion Criteria:

1. The patients aged between 40- 60 years old of both genders.
2. The patients in (Group A) should be diabetics for more than 10 years and free from any other systemic diseases with diabetic macular edema (by OCT).
3. The patients in (Group B) should be diabetics for more than 10 years and free from any other systemic diseases without diabetic macular edema (by OCT).
4. The patients in (Group C) should be free of any systemic diseases and normal macular thickness (by OCT)

Exclusion Criteria:

1. Previous history of any intraocular surgery, intravitreal injection, laser or refractive surgery.
2. Ocular surface disorders (e.g. dry eye) or any corneal pathology.
3. Corneal scars or epithelial dystrophies.
4. Use of any topical medications.
5. Elevated IOP, pregnancy or lactation.

It's a prospective cross section study. 159 eyes of 159 patients will be involved in this study, divided into three groups: (Group A) 53 eyes of diabetic patients with diabetic macular edema, (Group B) 53 eyes of diabetic patients without macular edema and (group C) 53 eyes of age matched control.