Leucomatous corneal opacity (leucoma simplex)
Leucomatous corneal opacity is a dense white opacity which results due to scarring of more than half of the stroma. A number of different presentations of leucomatous corneal opacity exist:

Adherent leucoma: results when healing occurs after perforation of cornea with incarceration of iris. The iris is adherent to the back of a leucomatous cornea. One of the major complication of adherent leucoma is Secondary glaucoma
Corneoiridic scar: if iris tissue is incarcerated and incorporated within the scar tissue, as occurs in healing of a large sloughed corneal ulcer, it is called a corneoiridic scar. Corneal facet: corneal surface depressed at the site of healing (due to less fibrous tissue); such a scar is called facet. Kerectasia: In this condition, corneal curvature is increased at the site of opacity (bulge due to weak scar). Presentation
Signs and symptoms include the following:

Loss of vision or blindness (when dense opacity covers the pupillary area)
Blurred vision (due to astigmatic effect and light scattering)
Glare

Complications
Congenital corneal opacity that affecting vision will cause amblyopia. That type of amblyopia is known as form-deprivation amblyopia (or amblyopia ex anopsia). Secondary changes in corneal opacity
Secondary changes may be seen in long-standing cases include: hyaline degeneration, calcareous degeneration, pigmentation and atheromatous ulceration. Causes
Congenital opacities may occur as developmental anomalies or following birth trauma. Causes of congenital corneal opacities include sclerocornea, trauma, ulcer, mucopolysaccharidosis, Peter’s anomaly, congenital hereditary endothelial dystrophy. Ocular trauma 
Corneal ulceration 
Xerophthalmia, caused by Vitamin A deficiency
Trachoma
Onchocerciasis
Mucous membrane pemphigoid: Ocular form of mucous membrane pemphigoid may cause corneal opacity and loss of vision.
The human cornea is a transparent membrane which allows light to pass through it. The word corneal opacification literally means loss of normal transparency of cornea. The term corneal opacity is used particularly for the loss of transparency of cornea due to scarring. Transparency of the cornea is dependent on the uniform diameter and the regular spacing and arrangement of the collagen fibrils within the stroma. Alterations in the spacing of collagen fibrils in a variety of conditions including corneal edema, scars, and macular corneal dystrophy is clinically manifested as corneal opacity. The term corneal blindness is commonly used to describe blindness due to corneal opacity. Types
Depending on the density, corneal opacity is graded as nebular, macular and leucomatous. Nebular corneal opacity
Nebular corneal opacity is a faint opacity which results due to superficial scars involving Bowmans layer and superficial stroma. A nebular corneal opacity allows the details of the iris to be seen through the opacity. A thin, diffuse nebula covering the pupillary area interferes more with vision than a strictly localized dense leucoma, so long as the latter does not block the whole pupillary area. This is because the leucoma stops all the light which falls upon it, whereas the nebula refracts it irregularly, allowing many of the rays to fall upon the retina where they blur the image formed by the regularly refracted rays. Macular corneal opacity
Macular corneal opacity is a semidense opacity produced when scarring involves about half the corneal stroma.