corneal opacities

This is a rare disorder with multiple anterior segment anomalies.  The corneal stroma is thinned in the range of 330 to 460 um with uniform steepening (no cone).  The epithelium may be irregular and edematous, the stroma is diffusely hazy, and the endothelium is irregular with many guttae.  Anterior polar cataracts are likely congenital and often require removal before the age of 20 years.  The pupils are often eccentric and difficult to dilate.  The iris stroma may appear atrophic.  Visual acuity, even in the aphakic condition, is in the range of 20/30 to 20/160.

Histological studies show attenuation of the endothelium with cellular overlapping and aggregates of fibrillar material that stains for cytokeratin.  Descemet membrane is thickened as is the epithelial basement membrane and both intracellular and extracellular lipid deposition is seen throughout the stroma and the Bowman membrane.

This rare congenital form of stromal dystrophy is sometimes considered a disorder of collagen fibrils with abnormally small diameters.  These may appear disorganized in areas.  Corneal opacities are often evident at birth or during the neonatal period.  Numerous small spots of fluffy, flaky deposits are found throughout the stroma creating a diffuse cloudy appearance and these may become more numerous with age indicating some progression.  The epithelium, Descemet membrane and the endothelium are not affected and the stroma is of normal or slightly increased thickness.  In some areas abnormal fibrillar layers are seen.  Although corneal erosions and photophobia are usually not clinically significant, acuity may be as low as hand motions and penetrating keratoplasty may be indicated.  In one series this was necessary at an average age of 20 years.  In the same series of 11 patients, 4 had strabismus, 3 eyes developed open angle glaucoma and band keratopathy was present in one patient.  Nystagmus has not been reported.

Deposition of abnormal decorin contributes to the stromal opacities. 

Schnyder corneal dystrophy has its onset early in life as a haziness of the central cornea with some peripheral extension.  The stroma gradually becomes more hazy and eventually in about 50% of patients yellow-white crystalline deposits can be seen in an annular pattern in the Bowman layer and the adjacent stroma just beneath. The remaining layers of the cornea are not involved.  The needle-shaped crystals are often birefringent and composed of cholesterol and phospholipids. There is considerable variation in the progression of disease and in the symmetry of disease in the two eyes.  Visual acuity may be relatively good in young people but older patients with denser central opacification eventually require corneal transplantation for better vision.

This stromal dystrophy may be congenital as it can be seen in the first years of life.  It is nonprogressive and generally has little clinical significance as it does not impair vision or require treatment in most cases.  It is usually diagnosed on routine examination from the presence of multiple, minute, whitish or grayish discrete opacities throughout the stroma.  The largest numbers are located centrally and posteriorly.  These may be flat, round or oval, and sometimes resemble snowflakes.  Keratocyte cell bodies contain cytoplasmic inclusions or vacuoles likely as the result of defective intracellular organelle trafficking.  Other layers such as the epithelium, Bowman layer, Descemet and endothelium are normal.  Expressivity is highly variable with considerable asymmetry of opacities in the two eyes and even unilateral involvement.

The corneal opacities in this disorder are usually located in the anterior stroma of the central cornea, and consist of discrete grayish-white, irregular granules with sharp margins.  The peripheral cornea and areas between the opacities remain clear.  The opacities may be apparent in the first decade but vision remains good throughout childhood.  The epithelial surface is usually smooth in children but adults can develop irregularities.  As the opacities enlarge and grow in number the cornea becomes increasingly opaque and older patients experience considerable loss of vision.  There is some variation in the number of opacities among individuals and considerable clinical heterogeneity occurs both within and between families.  The histologic appearance of the corneal deposits are said to be characteristic with eosinophilic deposits in the anterior stroma secondary to accumulations of mutant transforming growth factor beta induced protein.

The number and morphology of the granular deposits change throughout life, influenced to some extent by episodes of recurrent corneal erosions and age of patients.  Deposits become more annular and lattice-like in morphology, especially in the third decade and become more discoid by the fifth decade. 

It has been reported that the morphology and function of the meibomian glands are altered in this disease as well.

This disorder, reported so far in a single family, is an anterior corneal dystrophy with onset in the first decade of life.  The frequency of epithelial erosions tended to subside during adolescence but visual acuity continued to decline secondary to subepithelial nodular opacities and a generalized haze most dense centrally. No geographic lines are present and cystic changes in the epithelium were absent.  Bowman layer and deeper stuctures of the cornea are unaffected. Patients may have 20/30 vision into the fifth decade but after that it may decrease into the 20/400 range.  EM revealed accumulations of subepithelial fibrillar material.  Light microscopy and immunohistochemistry showed the material to be chondroitin-4-sulfate and dermatan sulfate.

Individuals have the onset of recurrent corneal erosions as a result of as yet unknown disease processes.  Onset is in the first decade of life (even in the first year of life)  often with some subepithelial haze or blebs while denser centrally located opacities develop with time.  Erosions often are precipitated by relatively minor trauma and are often difficult to treat, lasting for up to a week.  Fortunately, the erosions become less frequent as patients age and may cease altogether by the fifth decade of life.