Ophthalmology – Posterior Polymorphous Corneal Dystrophy

Basics

Description

Posterior polymorphous corneal dystrophy (PPCD/PPMD) is an inherited disorder of the corneal endothelium and Descemet membrane, usually bilateral but often markedly asymmetric.

The hallmark abnormality is transformation of corneal endothelial cells toward an:

Epithelial-like phenotype

This may produce:

• Vesicular posterior corneal lesions
• Band-like or geographic opacities
• Thickened/abnormal Descemet membrane
• Peripheral anterior synechiae
• Secondary glaucoma
• Corneal edema in more severe disease

Most affected patients remain:

Asymptomatic throughout life.

Clinical Importance

Although PPCD is usually mild, severe disease may cause:

• Progressive endothelial failure
• Stromal and epithelial edema
• Reduced visual acuity
• Secondary glaucoma
• Iridocorneal adhesions

In children, dense corneal edema or opacity can additionally cause:

Deprivation amblyopia

Epidemiology

PPCD is rare.

The exact:

• Incidence
• Prevalence

are unknown because many patients are asymptomatic and never diagnosed.

Inheritance

PPCD is most commonly inherited in an:

Autosomal dominant

pattern with variable expressivity.

Disease severity may differ substantially:

• Between family members
• Between the two eyes of the same patient

Genetics

Important modern genetic associations include:

• ZEB1
• OVOL2 regulatory variants
• GRHL2 regulatory variants

Older classifications described a COL8A2-associated “PPCD2” phenotype, but current molecular classification has evolved, and COL8A2 is more strongly associated with certain endothelial dystrophy phenotypes such as early-onset Fuchs disease rather than being a major cause of typical PPCD.

Genetic testing is most useful when:

• Disease is familial
• Presentation is early or severe
• Diagnosis is uncertain
• Counseling is desired

ZEB1-Associated PPCD

ZEB1 is an important cause of PPCD.

ZEB1 normally helps maintain:

Corneal endothelial identity

Loss of normal ZEB1 activity promotes:

• Endothelial-to-epithelial transformation
• Abnormal multilayering
• Epithelial marker expression

This explains much of the characteristic histology of PPCD.

Pathophysiology

Normal corneal endothelium consists of a:

• Single layer
• Nonregenerating
• Hexagonal endothelial cells

In PPCD, endothelial cells may acquire epithelial-like characteristics, including:

• Cellular proliferation
• Multilayering
• Desmosomes
• Cytokeratin expression
• Microvilli

These abnormal cells may migrate onto:

• Trabecular meshwork
• Peripheral iris

leading to:

• Peripheral anterior synechiae
• Angle obstruction
• Secondary glaucoma

Descemet Membrane Abnormalities

Descemet membrane may show:

• Irregular thickening
• Abnormal posterior collagenous material
• Focal excrescences
• Vesicular or band-like changes

These correspond clinically to the classic posterior corneal lesions.

Clinical Presentation

Most patients are:

Asymptomatic

and diagnosed incidentally.

Symptomatic patients may report:

• Blurred vision
• Glare
• Foreign-body sensation
• Photophobia
• Fluctuating vision

Symptoms usually result from:

• Corneal edema
• Irregular astigmatism
• Secondary glaucoma

Laterality

PPCD is generally:

Bilateral

but can be strikingly asymmetric.

Occasionally one eye appears clinically normal.

Slit-Lamp Findings

Classic posterior corneal findings include:

• Vesicles
• Band-like lesions
• Geographic opacities
• “Railroad-track” lesions
• Abnormal thickening of Descemet membrane

Vesicular Lesions

The classic lesion is a:

Small posterior corneal vesicle

which may be:

• Solitary
• Grouped
• Surrounded by a gray halo

They arise at the level of:

• Endothelium
• Descemet membrane

Band Lesions

Linear or curvilinear lesions may appear as:

Parallel tracks

sometimes described as:

• Railroad tracks
• Snail-track-like posterior opacities

These reflect broader areas of abnormal endothelium and Descemet membrane.

Geographic Lesions

Some patients develop:

• Irregular
• Geographic
• Sheet-like posterior corneal opacities

These may be associated with more extensive endothelial dysfunction.

Corneal Edema

Most patients do not develop significant edema.

In advanced disease:

• Endothelial pump failure

can produce:

• Stromal edema
• Epithelial edema
• Bullous keratopathy
• Subepithelial fibrosis

Pediatric Disease

Rare severe cases may present in infancy or childhood with:

• Corneal edema
• Corneal haze
• Reduced vision

This may cause:

Form-deprivation amblyopia

and requires early visual rehabilitation.

Iris and Angle Findings

Abnormal endothelial-like cells may extend across the angle.

Findings may include:

• Peripheral anterior synechiae
• Iridocorneal adhesions
• Distorted pupil in severe cases
• Abnormal angle membranes

These features increase the risk of:

Secondary glaucoma

Glaucoma

Glaucoma is the most important noncorneal complication.

Possible mechanisms include:

• Endothelial-like membrane extending over trabecular meshwork
• PAS formation
• Developmental angle abnormalities
• Open-angle outflow obstruction

Glaucoma can therefore occur with:

• Open angles
• Synechially closed angles
• Mixed mechanisms

Intraocular Pressure

IOP should be measured in all patients because glaucoma may be:

• Asymptomatic
• Progressive
• Disproportionate to the degree of corneal disease

Optic Nerve Assessment

Evaluate:

• Cup-to-disc ratio
• Neuroretinal rim
• RNFL OCT
• Macular GCIPL/GCC
• Visual fields

when age and visual function permit.

Gonioscopy

Gonioscopy is important to assess for:

• PAS
• Abnormal endothelial membrane
• Angle closure
• Developmental angle abnormalities

This helps determine the glaucoma mechanism.

Pachymetry

Central corneal thickness may increase with:

• Endothelial dysfunction
• Corneal edema

Serial pachymetry can help monitor:

• Progression
• Response to treatment

but is not specific for PPCD.

Specular Microscopy

Specular microscopy may show:

• Abnormal endothelial morphology
• Multilayered or vesicular lesions
• Reduced normal hexagonal pattern
• Highly irregular endothelial mosaic

It can help distinguish PPCD from other endothelial dystrophies.

Confocal Microscopy

In vivo confocal microscopy may demonstrate:

• Abnormal endothelial morphology
• Epithelial-like cells
• Vesicular lesions
• Multilayered cell patterns

It can be useful when:

• Slit-lamp visualization is poor
• Corneal edema obscures the posterior cornea

Anterior Segment OCT

AS-OCT may help document:

• Descemet abnormalities
• Posterior corneal lesions
• Corneal thickness
• Peripheral adhesions

but diagnosis is usually clinical.

Corneal Tomography

Corneal topography/tomography may be useful if there is:

• Significant astigmatism
• Suspected keratoconus
• Irregular corneal shape

Associated Corneal Disorders

PPCD has occasionally been reported with:

• Keratoconus
• Keratoglobus
• Other ectatic corneal disorders

Some ZEB1-associated phenotypes may have:

• Steeper corneas
• Abnormal corneal biomechanics

but these associations are variable.

Diagnosis

Diagnosis is usually based on:

• Characteristic slit-lamp appearance
• Bilaterality/asymmetry
• Family history
• Gonioscopy
• Specular or confocal microscopy when needed

Genetic Testing

Genetic testing may support the diagnosis in selected patients.

Consider especially when there is:

• Strong autosomal dominant family history
• Severe childhood disease
• Atypical presentation
• Need for family counseling

Differential Diagnosis

Important differentials include:

• Iridocorneal endothelial syndrome
• Fuchs endothelial corneal dystrophy
• Congenital hereditary endothelial dystrophy
• Descemet membrane tears
• Birth trauma
• Corneal edema from glaucoma
• Other posterior corneal dystrophies

PPCD vs ICE Syndrome

This is one of the most important distinctions.

PPCD

Usually:

• Bilateral
• Familial
• Younger onset
• Often relatively stable
• Endothelial cells have epithelial-like characteristics

ICE Syndrome

Typically:

• Unilateral
• Sporadic
• Adult onset
• Progressive
• More common in women
• Associated with:
• Corectopia
• Iris atrophy
• PAS
• Secondary glaucoma

PPCD vs Fuchs Endothelial Corneal Dystrophy

PPCD

• Vesicles/bands
• Often younger onset
• Epithelialized endothelial cells
• PAS may occur
• Autosomal dominant families possible

Fuchs

• Central guttae
• Progressive endothelial loss
• Central-to-peripheral edema
• Usually later onset
• No characteristic epithelial transformation of endothelium

PPCD vs Congenital Hereditary Endothelial Dystrophy

CHED typically presents with:

• Bilateral diffuse corneal edema
• Corneal clouding from infancy or childhood
• No classic posterior vesicles or railroad-track lesions

Modern CHED is primarily associated with:

SLC4A11

and usually follows an:

Autosomal recessive

inheritance pattern.

PPCD vs Descemet Tears

Descemet tears may occur after:

• Birth trauma
• Congenital glaucoma
• Surgery

They usually appear:

• Linear
• Localized

and lack the typical familial bilateral pattern of PPCD.

Treatment Principles

Most patients require:

Observation only

Treatment is directed toward complications rather than the dystrophy itself.

Mild Disease

If the patient is asymptomatic with:

• Clear cornea
• Normal IOP
• No progressive glaucoma

management consists of:

• Observation
• Periodic corneal examination
• Glaucoma surveillance

Hypertonic Saline

Hypertonic sodium chloride may reduce symptoms from:

• Epithelial edema
• Morning blur

It can be used as:

• Drops
• Ointment

However:

It does not reverse endothelial dysfunction or prevent progression.

Lubrication

Artificial tears may help if there is:

• Surface irritation
• Recurrent epithelial symptoms

Glaucoma Treatment

IOP-lowering therapy may include:

• Prostaglandin analogs
• Beta-blockers
• Carbonic anhydrase inhibitors
• Alpha-2 agonists

Treatment depends on:

• Angle status
• Severity
• Optic nerve damage

Glaucoma Surgery

Surgery may be required when:

• IOP remains uncontrolled
• PAS are extensive
• Glaucomatous progression occurs

Options include:

• Trabeculectomy
• Glaucoma drainage device
• Other glaucoma procedures based on angle anatomy

Angle surgery may have limited success in eyes with significant:

• PAS
• Endothelial membrane overgrowth

Endothelial Keratoplasty

For visually significant endothelial failure:

Endothelial keratoplasty is generally preferred over penetrating keratoplasty when anatomy permits.

Options include:

• DMEK
• DSAEK/DSEK

DMEK

DMEK offers:

• Rapid visual rehabilitation
• Minimal induced astigmatism
• Low rejection risk

However, PPCD can be technically challenging because of:

• Abnormal Descemet membrane
• PAS
• Irregular posterior corneal anatomy

Case selection is important.

DSAEK / DSEK

DSAEK may be preferred in some complex eyes because:

• Tissue is easier to manipulate
• Surgery may be more forgiving when the anterior segment is abnormal

Visual recovery may be slightly less optimal than with DMEK.

Penetrating Keratoplasty

PK is now generally reserved for cases with:

• Significant stromal scarring
• Extensive structural abnormalities
• Failed endothelial keratoplasty
• Anatomy unsuitable for endothelial keratoplasty

Pediatric Surgery

In children with severe corneal edema, early intervention may be needed to prevent:

Irreversible amblyopia

Management should include:

• Corneal surgery when indicated
• Optical correction
• Amblyopia therapy

Amblyopia

Children with asymmetric or bilateral corneal opacity require:

• Cycloplegic refraction
• Spectacle/contact lens correction
• Patching when appropriate
• Close pediatric ophthalmic follow-up

A clear graft alone does not guarantee good visual development.

Follow-Up

Follow-up should assess:

• Visual acuity
• Corneal clarity
• Corneal thickness
• IOP
• Gonioscopy
• Optic nerve
• OCT
• Visual fields when appropriate

Family Screening

Because many cases are autosomal dominant:

First-degree relatives may benefit from slit-lamp examination and IOP screening.

Family screening may reveal:

• Mild vesicular disease
• Previously unrecognized glaucoma

Prognosis

Overall prognosis is:

Excellent in most patients

because disease is often mild or slowly progressive.

Only a minority develop:

• Significant endothelial failure
• Severe glaucoma
• Need for corneal transplantation

Poor Prognostic Features

More severe disease is associated with:

• Early corneal edema
• Extensive PAS
• Secondary glaucoma
• Significant endothelial failure
• Dense stromal scarring

Complications

Potential complications include:

• Secondary glaucoma
• Peripheral anterior synechiae
• Corneal edema
• Bullous keratopathy
• Stromal scarring
• Reduced vision
• Amblyopia in children

Ophthalmology Pearls

• Posterior polymorphous corneal dystrophy is an inherited disorder of Descemet membrane and corneal endothelium, usually bilateral but often asymmetric.
• The classic lesions are posterior corneal vesicles, band-like “railroad-track” lesions, and geographic opacities.
• The fundamental cellular abnormality is epithelial-like transformation of corneal endothelial cells.
• Important modern genetic associations include ZEB1, OVOL2, and GRHL2.
• Most patients are asymptomatic and need only observation.
• Always screen for glaucoma, because abnormal endothelial cells can extend across the angle and produce PAS or trabecular obstruction.
• Gonioscopy is important to identify peripheral anterior synechiae and angle involvement.
• PPCD differs from ICE syndrome because PPCD is usually bilateral and familial, whereas ICE is typically unilateral, sporadic, and progressive.
• PPCD differs from Fuchs dystrophy by its vesicular/band lesions and epithelialized endothelium rather than central guttae.
• Hypertonic saline may improve symptoms from edema but does not correct endothelial failure.
• When corneal decompensation becomes visually significant, DMEK or DSAEK/DSEK is generally preferred over PK when anatomy is suitable.
• In children, severe corneal edema requires early treatment because of the risk of deprivation amblyopia.
• Family members may benefit from screening because PPCD is commonly autosomal dominant with variable expressivity.