Keratoconus

Comprehensive management of keratoconus — from early diagnosis and corneal cross-linking to scleral lenses, Intacs, CAIRS, and DALK corneal transplantation. Early assessment is essential to prevent irreversible vision loss.

What Is Keratoconus?

Keratoconus is a progressive condition in which the cornea — normally dome-shaped with a regular, smooth curve — progressively thins and bulges forward in an irregular pattern, typically in the inferior or central regions, producing a cone-like distortion of the corneal surface. This irregular shape scatters light as it enters the eye, causing blurred and distorted vision that worsens as the cone progresses and cannot be fully corrected with standard glasses.

Keratoconus affects approximately one in two thousand people in the general population, though estimates vary and subclinical forms detected by topographic screening are more common. It most commonly presents in the teenage years or early twenties, and progression tends to be most rapid during this period. The condition typically stabilises in the mid-to-late thirties, though this varies considerably between individuals.

The underlying cause involves a weakening of the corneal stromal collagen, though the precise molecular mechanism is still being characterised. Keratoconus has a genetic component — it is more common in individuals with a family history of the condition — and is strongly associated with habitual eye rubbing, which mechanically stresses the cornea and is thought to accelerate thinning. It is also more common in patients with atopic conditions such as eczema, hay fever, and asthma, and in Down syndrome.

Symptoms and Progression

Early keratoconus is often detected before symptoms appear — picked up incidentally on corneal topography performed as part of a laser vision correction assessment or a routine optometry check. The earliest symptomatic changes are typically mild blurring and difficulty getting a satisfactory glasses correction, followed by frequent prescription changes as the irregular astigmatism increases.

As keratoconus progresses, symptoms become more pronounced. Monocular diplopia (seeing a ghost image in one eye that disappears when the other eye is closed) is characteristic of irregular astigmatism. Photophobia (sensitivity to bright light) and glare become troublesome, particularly at night. Patients commonly describe difficulty with night driving, halos around lights, and visual fatigue. In advanced disease, the cornea may be visibly thinned and protuberant on clinical examination.

A rare but serious complication is acute hydrops — a sudden rupture of Descemet membrane allowing aqueous fluid to flood into the corneal stroma, causing acute painful corneal swelling and severe vision loss. Hydrops typically occurs in advanced keratoconus. It usually resolves over weeks to months but often leaves stromal scarring that may require transplantation. Common symptoms include:

• Progressive blurring and distortion of vision
• Monocular diplopia (ghost images in one eye)
• Increased light sensitivity and glare
• Frequent changes in glasses prescription
• Difficulty with night vision and driving
• Halos around lights
• Eye rubbing (which accelerates progression)

Diagnosis

Diagnosis of keratoconus is made by a combination of clinical examination and corneal imaging. On slit-lamp examination, a trained ophthalmologist may see Vogt's striae (fine stress lines in the posterior stroma), Fleischer ring (a brown iron deposition ring at the base of the cone), corneal thinning, and Munson's sign (a V-shaped indentation of the lower lid on downward gaze in advanced cases). However, clinical examination alone is insufficient to detect early or subclinical keratoconus.

Corneal topography maps the curvature of the anterior corneal surface and is the primary screening tool for keratoconus. Keratoconus produces characteristic patterns — inferior steepening, asymmetric astigmatism, and a skewed axis — that are detectable before symptoms develop. Scheimpflug imaging (Pentacam or Galilei) provides full tomographic data: anterior and posterior corneal surface curvature, corneal thickness (pachymetry) across the entire cornea, and an elevation map relative to a best-fit sphere. The posterior surface and the thinnest point measurement are particularly important for early detection and for cross-linking candidacy assessment.

Progression is determined by comparing serial tomographic measurements over time. A statistically significant change in keratometric steepness, a reduction in minimum corneal thickness, or worsening of topographic indices on two consecutive measurements confirms progression and strengthens the indication for cross-linking.

Non-Surgical Visual Correction

The goal of non-surgical management is to maximise visual function using optical means while the disease is stabilised or monitored. The appropriate option depends on the degree of corneal irregularity.

Corneal Cross-Linking (CXL)

Corneal collagen cross-linking is the only treatment that addresses the underlying cause of keratoconus — the weakened stromal collagen — rather than managing its optical consequences. By stiffening the corneal stroma, CXL halts or significantly slows the progression of keratoconus in the majority of appropriately selected patients. It does not improve existing corneal shape or visual acuity, but in a condition where progression leads to irreversible structural damage and, ultimately, the need for transplantation, halting progression is the most important intervention available.

Intacs — Intrastromal Corneal Ring Segments

Intacs are thin, semi-circular polymethylmethacrylate (PMMA) ring segments that are implanted into tunnels created in the mid-peripheral corneal stroma using a femtosecond laser. By redistributing the mechanical forces within the corneal stroma, Intacs flatten the central cornea and reduce the degree of irregular astigmatism. They do not treat the underlying keratoconus — the condition continues to progress unless cross-linking has been performed — but they can improve contact lens tolerance and, in some patients, visual acuity without lenses.

Intacs are most useful in patients with moderate keratoconus who are intolerant of contact lenses and are not yet advanced enough to require a corneal transplant, or as a bridging procedure to improve contact lens wear while awaiting transplantation. They are most effective when the keratoconus is inferiorly centred, the cone is not too advanced, and there is no significant central corneal scarring. Intacs can be removed or exchanged if the result is not satisfactory, though the corneal tunnels remain permanently. Cross-linking is typically recommended in combination with Intacs if progression has been documented.

CAIRS — Corneal Allogenic Intrastromal Ring Segments

CAIRS is an emerging technique that uses donor corneal stromal tissue — rather than synthetic plastic rings — as the intrastromal implant for keratoconus. Strips of donor corneal stroma are prepared from bank tissue and implanted into femtosecond laser–created tunnels in the recipient cornea in a similar manner to synthetic Intacs. The theoretical advantage of using biological tissue is biocompatibility — the implant integrates with the host stroma rather than remaining as a foreign body — and the potential for greater customisation of the implant dimensions and placement.

Published results from the centres where CAIRS has been developed — primarily in India and Egypt — are promising, with studies reporting significant corneal flattening and improvements in corrected visual acuity. Advantages over synthetic rings may include a reduced risk of extrusion or channel infection, as well as the possibility of using CAIRS in eyes too advanced for conventional Intacs.

Corneal Transplantation for Keratoconus

The majority of patients with keratoconus who undergo timely cross-linking and appropriate contact lens management will not require a corneal transplant. However, transplantation becomes necessary when the cornea has advanced to the point where it cannot be adequately corrected with any contact lens modality, when acute hydrops has caused significant corneal scarring, or when the cornea is too thin for cross-linking to be safely performed.

For keratoconus, the preferred corneal transplant technique is DALK — deep anterior lamellar keratoplasty. DALK replaces the diseased epithelium and stroma while preserving the patient's own Descemet membrane and endothelium. Because keratoconus primarily affects the anterior stroma and the endothelium is typically healthy, DALK achieves the goals of transplantation without introducing donor endothelium. The critical advantage is the elimination of endothelial rejection — the main cause of late graft failure in full-thickness transplants. Long-term graft survival in DALK for keratoconus is significantly better than PKP.

PKP (full-thickness corneal transplant) remains appropriate in keratoconus when DALK is not technically feasible — for example, when there has been prior hydrops with Descemet membrane rupture and posterior corneal scarring that makes the critical tissue separation impossible. Full detail on both procedures is available on the corneal surgery page.

Surgeon Training and Experience

Dr Ross MacIntyre MD FRANZCO undertook subspecialty fellowship training in cornea, complex cataract, and refractive surgery at the Wilmer Eye Institute at Johns Hopkins University in Baltimore. Fellowship training at Wilmer — one of the most highly regarded ophthalmic referral centres in the world — provides concentrated experience with the full spectrum of corneal disease including keratoconus in all stages, cross-linking candidacy assessment, and the range of surgical options from Intacs through to DALK and PKP. He subsequently completed a corneal fellowship at the Royal Victorian Eye and Ear Hospital in Melbourne.

Dr MacIntyre continues as a Staff Specialist on the RVEEH Cornea Unit, where he is involved in the management of complex keratoconus cases including those referred for surgical management after failing conservative treatment. He consults at Northern Eye Consultants, Northpark Private Hospital, Bundoora. For further detail on his training and credentials, see drmacintyre.com.