Ophthalmology – Fuchs’ Corneal Dystrophy

Basics

Description

Fuchs’ corneal dystrophy, more precisely called Fuchs endothelial corneal dystrophy (FECD), is a progressive, usually bilateral and noninflammatory disorder of the corneal endothelium. It is characterized by the formation of focal excrescences of Descemet membrane known as corneal guttae, progressive loss and dysfunction of endothelial cells, and subsequent stromal and epithelial corneal edema.

The corneal endothelium normally maintains corneal deturgescence by acting as both a permeability barrier and an active fluid pump. As endothelial cells become dysfunctional and decrease in number, the cornea gradually loses its ability to remain dehydrated and transparent.

Patients typically complain of blurred vision and glare that are worse in the morning after awakening. As disease progresses, epithelial edema may lead to formation of painful bullae. Rupture of these bullae can cause recurrent erosions, pain, photophobia, and tearing.

Epidemiology

Fuchs dystrophy most commonly becomes clinically significant in the fifth and sixth decades of life, although corneal guttae may be detected earlier.

A rare early-onset form can present during childhood or the first few decades of life.

Women are affected more commonly than men.

The prevalence of clinically apparent disease increases with age, and corneal guttae are relatively common in older adults.

Risk Factors

The strongest risk factor is increasing age.

Other factors that can worsen endothelial dysfunction include elevated intraocular pressure, ocular inflammation, and previous intraocular surgery, particularly cataract surgery.

Because patients with Fuchs dystrophy already have reduced endothelial reserve, additional endothelial cell loss during intraocular surgery can precipitate clinically significant corneal edema.

Genetics

Fuchs endothelial corneal dystrophy has a strong genetic component but is genetically heterogeneous.

Some families show autosomal dominant inheritance with incomplete penetrance and variable expression.

Several genetic loci and genes have been associated with FECD. Early-onset disease has been linked to mutations in COL8A2, while common late-onset disease is associated with other genetic abnormalities, including variants involving TCF4 in many populations.

Because expression can vary markedly even within the same family, relatives with the same pathogenic variant may have very different clinical severity.

Pathophysiology

The primary abnormality is progressive dysfunction and loss of corneal endothelial cells.

The diseased endothelium produces abnormal Descemet membrane, resulting in focal collagenous excrescences called guttae. Over time, Descemet membrane becomes abnormally thickened.

As endothelial cell density falls, the remaining cells enlarge and change shape in an attempt to cover the posterior corneal surface. These changes are described as polymegathism, meaning variation in cell size, and pleomorphism or polymorphism, meaning variation in cell shape.

Eventually, the endothelial barrier and pump functions become insufficient. Failure of the endothelial Na+/K+-ATPase-dependent fluid transport system allows fluid to accumulate in the corneal stroma.

Stromal edema initially develops posteriorly and then progresses anteriorly. With more advanced disease, the epithelium becomes edematous and develops microcysts that coalesce into epithelial bullae.

Chronic edema may eventually cause subepithelial fibrosis, anterior basement membrane abnormalities, corneal scarring, and superficial neovascularization.

Etiology

Endothelial cell density normally decreases throughout life. Patients with Fuchs dystrophy experience an accelerated and pathologic loss of endothelial cells.

In infancy, endothelial cell density is much higher than in adulthood. Because human corneal endothelial cells have very limited ability to regenerate, progressive cell loss gradually reduces endothelial reserve.

Additional endothelial injury from cataract surgery, other intraocular procedures, inflammation, trauma, or elevated intraocular pressure may accelerate decompensation.

Commonly Associated Conditions

Fuchs dystrophy is frequently associated with cataract, particularly because both conditions become more common with age.

Other associations include open-angle glaucoma, angle-closure glaucoma, recurrent epithelial erosions, and painful bullous keratopathy.

Keratoconus has occasionally been reported in association with Fuchs dystrophy but is uncommon.

Diagnosis

History

Patients commonly report gradually progressive blurred vision and glare.

A particularly characteristic symptom is that vision is worse after awakening and improves during the day. During sleep, the closed eyelids reduce evaporation from the corneal surface, allowing corneal edema to increase. After awakening, evaporation gradually helps reduce the edema.

Patients with more advanced disease may describe pain, foreign-body sensation, photophobia, and tearing, especially when epithelial bullae rupture.

A history of previous cataract surgery, other intraocular surgery, glaucoma, or uveitis is important because these conditions can accelerate endothelial failure.

Physical Examination

A complete ophthalmic examination should include visual acuity, intraocular pressure, slit-lamp examination, and dilated fundus examination when the posterior segment can be visualized.

Early Disease

In early disease, slit-lamp examination shows central corneal guttae.

These may be best appreciated using direct illumination, specular reflection, or retroillumination.

The guttae commonly begin centrally and gradually spread toward the peripheral cornea.

Moderate Disease

As disease progresses, the posterior corneal surface develops a characteristic beaten-metal or hammered-metal appearance because of numerous confluent guttae and associated endothelial pigmentation.

Descemet membrane becomes thickened.

Stromal edema develops, initially in the posterior cornea. Descemet folds may become visible as edema worsens.

Advanced Disease

Progressive edema eventually reaches the epithelium, producing microcystic epithelial edema.

The epithelial microcysts may merge into larger bullae. Rupture of these bullae produces significant pain and recurrent epithelial defects.

End-stage disease may show subepithelial fibrosis, anterior stromal scarring, superficial vascularization, and chronic bullous keratopathy.

Diagnostic Testing

Pachymetry

Corneal pachymetry measures central corneal thickness.

An increase in corneal thickness can indicate progressive edema and reduced endothelial function. Serial measurements can help assess progression.

However, corneal thickness should always be interpreted together with symptoms, slit-lamp findings, and endothelial imaging.

Specular Microscopy

Specular microscopy allows evaluation of endothelial cell density and morphology.

It can demonstrate reduced endothelial cell counts, guttae, polymegathism, and pleomorphism.

In advanced disease, dense guttae or severe corneal edema may make accurate endothelial cell counting difficult.

Confocal Microscopy

Confocal microscopy can provide additional information about endothelial morphology and may be useful when conventional visualization is limited.

B-Scan Ultrasonography

If severe corneal edema or coexisting cataract prevents adequate visualization of the posterior segment, B-scan ultrasonography can be used to exclude significant retinal or vitreous pathology.

Pathological Findings

Histopathology demonstrates a diffusely thickened Descemet membrane with characteristic excrescences or guttae.

There is a reduced number of endothelial cells, often with marked variation in cell size and shape.

Advanced disease may show subepithelial fibrosis, epithelial basement membrane abnormalities, bullous keratopathy, and superficial corneal neovascularization.

Differential Diagnosis

The differential diagnosis includes other causes of corneal endothelial failure or edema.

Important possibilities include pseudophakic or aphakic bullous keratopathy, posterior polymorphous corneal dystrophy, congenital hereditary endothelial dystrophy, iridocorneal endothelial syndrome, and chronic inflammatory or infectious endothelial disease.

Central herpetic disciform keratitis can cause corneal edema but is usually associated with inflammatory signs and a different clinical history.

Corneal pseudoguttae may occur transiently after trauma, intraocular inflammation, infection, or toxic injury and should be distinguished from true Fuchs dystrophy.

Treatment

Treatment depends on the severity of symptoms and degree of corneal decompensation.

First-Line Medical Treatment

For mild to moderate corneal edema, hypertonic sodium chloride 5% drops can be used during the day.

Hypertonic sodium chloride ointment is particularly useful at bedtime because it provides longer contact with the ocular surface.

These treatments draw water from the corneal epithelium and may temporarily improve vision and discomfort. They do not reverse the underlying endothelial disease or stop its progression.

Morning Edema

Because edema is often worse after sleep, some patients obtain temporary symptomatic benefit from increasing evaporation after awakening.

Historically, use of a hair dryer at arm’s length with cool or low-warm airflow directed toward the closed or blinking eyes has been suggested to encourage evaporation, although this is a symptomatic measure rather than disease-modifying therapy.

Management of Elevated Intraocular Pressure

If intraocular pressure is elevated, appropriate glaucoma therapy should be initiated because excessive pressure can further compromise endothelial function.

Choice of medication should take the overall ocular condition into account.

Management of Bullous Keratopathy

Painful epithelial bullae may be managed temporarily with lubrication and a therapeutic bandage contact lens.

Because an epithelial defect increases the risk of microbial keratitis, these patients require appropriate monitoring.

Recurrent or persistent painful bullae in an eye with poor visual potential may require additional palliative procedures, but in an eye with useful visual potential definitive endothelial replacement is usually preferred.

Surgical Treatment

Definitive treatment is indicated when corneal edema causes significant visual impairment or painful bullous keratopathy that is not adequately controlled medically.

Endothelial Keratoplasty

For most patients with Fuchs dystrophy who do not have significant anterior stromal scarring, endothelial keratoplasty is preferred.

DMEK

Descemet membrane endothelial keratoplasty (DMEK) replaces diseased Descemet membrane and endothelium with donor Descemet membrane and endothelial cells.

It generally provides rapid visual rehabilitation, minimal induced astigmatism, and excellent optical quality.

DSAEK/DSEK

Descemet stripping automated endothelial keratoplasty (DSAEK) or DSEK replaces the diseased endothelium and Descemet membrane along with a thin layer of donor posterior stroma.

It remains an effective option, although DMEK often provides faster visual recovery and better final optical quality when technically suitable.

Penetrating Keratoplasty

Penetrating keratoplasty (PKP) replaces the full thickness of the cornea.

It is generally reserved for patients with advanced Fuchs dystrophy who have substantial anterior stromal scarring, subepithelial fibrosis, or other corneal pathology that would limit vision even after endothelial replacement alone.

Compared with endothelial keratoplasty, PKP usually has a longer visual recovery period and greater risk of induced astigmatism and wound-related complications.

Fuchs Dystrophy and Cataract Surgery

Cataract and Fuchs dystrophy commonly coexist.

Before cataract surgery, the surgeon should assess the severity of endothelial disease using the clinical examination, pachymetry, endothelial imaging when possible, visual symptoms, and extent of guttae or edema.

Patients with relatively mild disease may undergo cataract surgery alone, but they should be counseled that postoperative corneal edema may be prolonged and that endothelial keratoplasty may eventually be required.

Patients with significant endothelial dysfunction and a visually important cataract may benefit from combined cataract surgery and endothelial keratoplasty, sometimes called a triple procedure.

Historical thresholds such as endothelial cell density below approximately 1,000 cells/mm² or markedly increased corneal thickness have been used to estimate risk, but contemporary surgical decisions are individualized and should not rely on a single numerical cutoff.

Follow-Up

Follow-up frequency depends on disease severity.

Patients with mild, stable disease may be examined approximately every 6–12 months, while those with progressive edema or declining vision require closer follow-up.

Monitoring should include visual acuity, slit-lamp examination, intraocular pressure, and assessment of corneal thickness or endothelial status when clinically useful.

Patients with epithelial defects or ruptured bullae need closer follow-up because of the risk of infectious keratitis.

Patient Education

Patients should understand that Fuchs dystrophy is usually a slowly progressive condition and that the rate of progression varies considerably between individuals.

Morning blur is characteristic because corneal edema increases while the eyelids are closed during sleep.

Hypertonic saline drops may sting, while ointment frequently causes temporary blur. These effects should be explained so that patients are not unnecessarily alarmed.

Patients considering cataract surgery should understand that their reduced endothelial reserve increases the risk of persistent postoperative corneal edema and eventual need for endothelial transplantation.

Prognosis

The natural course is progressive but variable.

Many patients remain mildly symptomatic for years, while others develop clinically significant corneal edema and visual impairment.

Modern endothelial keratoplasty has greatly improved prognosis. DMEK and DSAEK generally provide excellent corneal clarity and substantial visual improvement in appropriately selected patients.

Final vision depends not only on the cornea but also on other ocular conditions such as cataract, glaucoma, macular disease, and optic nerve disease.

Complications

Untreated advanced disease may lead to painful bullous keratopathy, recurrent epithelial erosions, infectious keratitis, corneal ulceration, fibrosis, scarring, and neovascularization.

Potential complications after corneal transplantation include graft rejection, graft failure, glaucoma, infection, astigmatism, wound problems, retinal detachment, uveitis, and endophthalmitis.

Following endothelial keratoplasty, additional procedure-specific complications can include graft detachment requiring rebubbling, primary graft failure, and endothelial cell loss.