Corneal ectasia in keratoconus is revealed on 
computerized corneal topography map

ICD-10 Diagnosis Codes:

H18.611–Keratoconus, stable, right eye
H18.612–Keratoconus, stable, left eye
H18.613–Keratoconus, stable, bilateral




Corneal Opacity And Other Disorders Of Cornea


Keratoconus is a disease of the cornea.  It is characterized by progressive thinning of the corneal stroma and a progressive steepening in the shape of the cornea. 

Keratoconus is a non-inflammatory thinning and protrusion of the cornea.  It is usually bilateral, but is often asymmetric in its presentation.  As the disease progresses the patient experiences blurred or distorted vision.  Visual impairment secondary to irregular astigmatism can be mild or severe depending on the degree of corneal ectasia.  In advanced keratoconus, vision loss can occur from acute corneal hydrops and corneal scarring.

Keratoconus typically is an isolated ocular disorder but can be seen more commonly in patients with Down’s Syndrome, atopic disease, mitral valve prolapse and patients that exhibit chronic eye rubbing (often from atopic disease).

Structural Damage to the Eye

  • Steepening of the cornea especially the inferior region
  • Thinning of the corneal apex
  • Fine “tension” lines in the deep stroma (Vogt’s striae)
  • All these findings producing mild to severe irregular corneal astigmatism
  • Bulging of the inferior cornea to the point of producing a visible cone when the patient looks down (Munson’s sign)
  • Ring of iron deposit accumulates in corneal endothelium at the base of the cone (Fleischer Ring)
  • Breaks in the posterior cornea lead to severe stromal edema (acute corneal hydrops)

Functional Change in the Visual System

  • Decreased vision – quantitatitve and qualitative
  • Glare
  • Halos around lights
  • Monocular diplopia
  • Ghost images
  • Multiple unsatisfactory attempts in obtaining good visual acuity with eyeglasses
  • Often reports of functional vision only when wearing contact lenses, especially gas permeable lenses
  • Can also report contact lens intolerance 

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

  • Make a definitive diagnosis of keratoconus
  • Determine if the patient can function adequately with an eyeglasses prescription
  • If not, prescribe medically necessary contact lenses

Patient History

Patients with keratoconus may present with any of the following signs and symptoms:

  • None
  • Systemic history of Down’s Syndrome, atopic disease or mitral valve prolapse
  • Photophobia
  • Halos around lights
  • Monocular diplopia
  • Variable and inconsistent refractions
  • History of multiple spectacle prescriptions in a short period of time
  • Complaints of distortion rather than blurred vision at both distance and near

External Examination with Biomicroscopy

Clinical Appearance of the Keratoconic Cornea

  • Pronounced conical corneal shape
  • Pronounced corneal thinning
  • Opacities present at the corneal apex
  • Retinoscopy shows a scissoring reflex
  • Direct ophthalmoscopy may show a shadow
  • Punctate epitheliopathy with and without contact lens wear
  • Increased visibility of corneal nerves
Clinical Appearance of the Keratoconic Cornea

  • Paracentral thinning of the cornea
  • Bulging of the cornea
  • Subepithelial corneal scarring is seen as the disease progresses
  • Scarring occurs when ruptures in Bowman’s membrane are filled with connective tissue


Computerized Corneal Topography


  • Document the shape and physical features of the anterior corneal surface
  • Identification and follow-up for corneal disease causing irregular astigmatism
  • To help plan a treatment program
  • To document the progress or lack of progress of keratoconus
  • To document the delivery of medical treatment
  • To document the response to treatment


Anterior Segment Imaging

  • In-vivo imaging of the cornea
  • Optical coherence tomography produces a cross-section of the cornea showing the anatomy and quality of the tissue
  • Measures corneal thickness
  • Anterior segment imaging can determine the location of the most severe area of cornea thinning and ectasia

  • Paracentral thinning of the cornea
  • Cornea ectasia
  • Abnormal corneal shape

Although keratoconus can be classified by the shape of the cone, by the central keratometric measurement, or by its level of severity in producing visual impairment, a common system of classification uses clinical findings to define four stages of keratoconus.

Stage 1 – Mild Keratoconus

  • Egg-shaped keratometry mires
  • Keratometry readings < 45.00 D in both meridians
  • Inferior steepening on topography map
  • No visible corneal signs
Stage 2 – Moderate Keratoconus

  • Irregular keratometry mires
  • Keratometry readings 45.00 D to 52.00 D in both meridians
  • Pronounced corneal steepening
  • Fleischer ring segments
  • Vogt’s striae
  • Other corneal scars
Stage 3 – Advanced Keratoconus

  • Severe corneal scarring
  • Keratometry readings > 52.00 D in both meridians
  • Difficulty tolerating contact lenses or obtaining functional vision
Stage 4 – Severe Keratoconus

  • Keratometry readings > 62.00 D in both meridians
  • Contact lens intolerance is common 
  • Surgical intervention is usually required to regain functional vision

Corneal Warpage due to Contact Lens Wear

Wearing contact lenses, especially high-riding gas permeable lenses, can produce reversible irregular corneal astigmatism.  The topographic appearance can easily mimic early keratoconus.  Refitting the lenses and monitoring the condition over time may be the only way to confirm the lack of corneal disease.

Other Causes of Irregular Astigmatism

Consider other causes of irregular corneal astigmatism from corneal scarring – prior corneal surgery including refractive surgery, trauma and healed past infections.  Iron deposits can also occur in patients with pterygium, surgical scars and central depression from refractive surgery.

Induced Hypoxia or Early Signs of Endothelial Failure

Stromal striations similar to Vogt’s striae can occur in severe contact lens-related corneal edema or the late stages of Fuchs’ endothelial dystrophy.

Terrien Marginal Corneal Degeneration

Terrrien marginal corneal degeneration is a mild inflammatory disease affecting the superior limbus, which can induce irregular against-the-rule astigmatism from the neovascularization and lipid deposits on the cornea.


Keratoglobus is a rare disease in which the entire cornea, from limbus to limbus, thins.  The thinning can cause the cornea to spontaneous perforate.

Posterior Keratoconus

Posterior keratoconus is a rare, congenital disease were the posterior cornea protrudes into the stroma.

Pellucid Marginal Degeneration

This condition is characterized by a corneal thinning that occurs about a millimeter above the inferior limbus which leads to ectasia.  Although pellucid marginal degeneration is similar to keratoconus, most eye doctors believe that they are two distinct conditions.

Pellucid may have significantly less effect on qualitative vision, may occur in older patients and often shows slower to sometimes clinically insignificant progression.

Topographic Characteristics

  • Inferior crescent-shaped area of peripheral corneal thinning
  • Corneal thinning results in advanced against-the-rule astigmatism
  • The astigmatism is characterized by the “bear claw” or “kissing doves” pattern

Treatment with Eyeglasses

  • Patients with mild keratoconus can usually obtain functional vision with glasses
  • As the disease progresses patients may need new eyeglass prescriptions as frequently as every six months

Mechanical Treatment

According to the Collaborative Longitudinal Evaluation of Keratoconus (CLEK) Study, over 70% of patients with keratoconus wear contact lenses.

Treatment with Contact Lenses

  • Soft contact lenses
  • Gas permeable lenses
  • Hybrid lenses
  • Scleral lenses
  • Piggyback lens system

Central bearing reveals a flat
cornea-contact lens relationship


Pharmacologic Treatment

  • Hypertonic eye drops and ointments to manage acute corneal hydrops
  • Cycloplegic eye drops to reduce eye pain in acute corneal hydrops
  • Topical steroid eye drops to reduce inflammation in acute corneal hydrops

Surgical Treatment

Consider surgical treatment options if mechanical and pharmacologic treatments are unsuccessful.

  • Amniotic membrane placement
  • Penetrating keratoplasty
  • Lamellar keratoplasty
  • Excimer laser corneal ablation
  • Intact corneal implants
  • Corneal collagen cross-linking with ultraviolet A and ribloflavin (currently under investigation)
  • Sulfur hexafluride gas (SF6) to reduce corneal edema during episodes of acute keratoconus (currently under investigation)

Amiotic 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

1.  Weissman B.  Keratoconus.  Medscape/EMedicine.  22 Apr 2014.  Last accessed August 17, 2014.
2.  John T.  A Wide-Angle View of Keratoconus.  RevOptom.  Oct 2012.  Last accessed August 17, 2014.
3.  Shovlin J.  Softer Approach to Keratoconus?  RevOptom.  15 June 2012.  Last accessed August 17, 2014.


Anterior segment ultrasound

Corneal pachymetry


Corneal topography

External ocular photography

Anterior segment imaging

Bandage contact lens

Treatment with contact lens

Amniotic membrane placement


  • 50-200 cases per 100,000 population
  • Most keratoconus cases appear spontaneously, although approximately 14% of cases present with evidence of genetic transmission


  • An equal incidence of keratoconus occurs in males and females

Risk Factors

  • Ocular allergies
  • Rigid contact lens wear
  • Vigorous eye rubbing