H18.231-233 Secondary Corneal Edema

Corneal edema is a clinical sign of corneal disease.  The condition is characterized by an increase in corneal thickness secondary to an abnormal accumulation of fluid.  The excess fluid produces a swelling of the corneal tissue and can result in a loss of stromal transparency that produces blurred vision or visual impairment. 

The layers of the cornea are optically transparent so that the entire structure can transmit visible light.  When viewed in cross-section, the cornea is a basic structure of two covering layers with a central collagen stroma.  The outer covering layer is called the anterior cornea.  It is composed of the corneal epithelium and a basement membrane called Bowman’s membrane.  This layer functions as a semi-permeable membrane that keeps pathogens out of the eye but allows nutrients from the pre-ocular tear film to nourish the anterior cornea.

The middle layer of the cornea is called the stroma.  This layer comprises over 90% of the cornea’s thickness and is composed of tightly packed collagen fibrils in an orderly lamellar arrangement.  The spacing and arrangement of the fibrils makes the corneal stroma optically transparent.  To maintain optical transparency, the stroma must be maintained in a state of relative deturgescence and the normal level of stromal hydration is 78% water.  The inability to maintain stromal deturgescenece can result in corneal edema and a loss of stromal transparency.

The inner covering layer is called the posterior cornea.  It is composed of the corneal endothelium and Descemet’s membrane.  This layer fuctions as a semi-permeable membrane that controls fluid and solute transport across the posterior surface of the cornea.  Because of the strength and flexibility of Descemet’s membrane, the posterior cornea also serves as a barrier against injury.

The main goal of the diagnostic evaluation in a patient with corneal edema is to accomplish the following:

• Determine the underlying condition producing the corneal edema
• Treat the underlying condition
• Treat the corneal edema, if necessary

Patient History

Patients will usually present with the following symptoms:

• Blurred vision
• Fluctuating vision
• Cloudy vision
• Sensitivity to bright light
• Halos around point sources of light
• Contact lens intolerance

External Examination with Biomicroscopy

• Loss of stromal transparency
• Folds in Descemet’s membrane
• Obvious thickening of the cornea
• Corneal guttata
• Epithelial edema

DIAGNOSTIC TESTS

External Ocular Photography

• To document the progress or lack of progress of corneal edema
• To help plan a treatment program
• To document the delivery and response to medical treatment

Specular Endothelial Microscopy

• To document the progress or lack of progress of corneal edema
• To visualize and analyze the corneal endothelium
• To document the progress or lack of progress of a corneal endotheliopathy
• To help plan a treatment program
• To document the delivery and response to medical treatment

Congential Corneal Edema

Most cases of congenital corneal edema result from birth trauma, congenital glaucoma, or congenital hereditary corneal endothelial dystrophy.  These are rarely seen in a primary eye care practice.

Acquired Corneal Edema

Acquired corneal edema may occur with many eye diseases and conditions and these include the primary and secondary corneal endotheliopathies.

Corneal edema has few conditions that mimic its appearance.  A few could be:

Corneal scarring from prior injury  

In this case the lack of transparency will be confined to the stromal area and likely associated with a traumatic history.

Severe Corneal Edema Acute hydrops in advanced keratoconus  Severe loss of stromal transparency

Corneal scarring from prior surgery

Focal areas of scarring can be confused with edema (i.e. scarring at an incision site from prior cataract surgery or corneal surgery – especially prior PRK or LASIK).

In both cases, scars take on a denser appearance, often have very irregular patterns unless associated with an incision site and should have a supportive history.  The only differential diagnosis relates to uncovering the underlying etiology for the apparent corneal disease.

Because corneal edema can be caused by various eye diseases and conditions, the condition is treated according to the cause.  The first goal of treating patients with corneal edema is to reduce the edema and the associated symptoms of blurred vision and ocular discomfort.  Second, best practices treatment guidelines indicate treatment of the underlying condition producing the corneal edema.

Preventative Treatment

Amniotic Membrane Inserts:

		ProKera Amniotic Membrane Insert Cryopreserved amniotic membrane graft fastened to a thermoplastic symblepharon ring The device acts as a self-retaining biological bandage Promotes reepithelialization
BioDOptix Amniotic Membrane Insert Dehydrated amniotic membrane graft

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