An Introduction to the National Healthcare Group (NHG) Eye Institute, and Keratoconus
Since its inception in 2001, the NHG Eye Institute has continued to address the increasing demand for eye care services, research and training. It incorporates Tan Tock Seng Hospital’s (TTSH) Department of Ophthalmology as its flagship clinical unit, and delivers quality tertiary and primary eye care to patients in Singapore and the region. With more than 32 fellowship-trained consultants on-board, the Institute covers the entire spectrum of ophthalmic subspecialties, providing comprehensive diagnosis and advanced treatment for both common and complex eye diseases.
In part one of ‘Eye Discoveries’ series by the NHG Eye Institute, we will be taking a look at Keratoconus – its cause, symptoms and treatment options.
What Is Keratoconus?
Keratoconus is an uncommon condition in which the cornea (the clear front window of the eye) becomes progressively thin and protrudes outward. Keratoconus literally means a conical-shaped cornea, which is an abnormal shape that can cause serious distortion and reduction of vision.
What Causes Keratoconus?
A patient with Keratoconus
Despite ongoing research efforts, the cause of Keratoconus remains unknown. Although Keratoconus is not generally considered an inherited disorder, it still presents a high chance of one in ten individuals having a blood relative with the condition. Eye irritation from vigorous rubbing, although not the cause of Keratoconus, can contribute to the disease’s progression. Therefore, patients with Keratoconus are advised to avoid rubbing their eyes.
Other risk factors include medical conditions such as Marfan’s syndrome, Ehlers-Danlos syndrome, Down syndrome, hay fever, and vernal keratoconjunctivitis.
What Are the Symptoms of Keratoconus?
At the onset of the disease, patients may be asymptomatic, with their vision only slightly affected. Symptoms usually appear during a patient’s late teens or early twenties, in the form of increasingly blurred and distorted vision. In the early stages, there may be no obvious findings on slit-lamp examination of the cornea, and the diagnosis can only be made by computerised corneal topography.
As the disease progresses and the cornea steepens, significant astigmatism develops, and vision becomes noticeably distorted. Subsequently, increased myopia and astigmatism result in spectacle intolerance or irregular astigmatism, which cannot be optimally corrected by spectacles. This may necessitate the use of rigid contact lenses. Keratoconus usually affects both eyes, though each eye may be affected differently. The disease will often progress throughout a patient’s mid-thirties, at which time progression slows and often stops.
During the course of the disease, the cornea can suddenly develop edema (acute hydrops) when a tiny dehiscence occurs in the internal layers of the cornea caused by the stretching of the cornea protrusion. This results in a sudden decrease in vision, irritation, glares and halos. The swelling may persist for weeks or months while the crack heals and is gradually replaced by scar tissue.
Diagnosis is made by the eye specialist via slit-lamp examination, keratometry, retinoscopy and corneal topography, which can demonstrate evidence of corneal protrusion and irregularity.
How Is Keratoconus Treated?
Mild cases can be successfully treated with prescription spectacles or specially-fitted contact lenses.
When vision is no longer satisfactory even with the use of glasses or contact lenses, surgery is often recommended. When progression of the disease is found to be rapid, particularly among younger patients, Cornea Collagen Cross-linking may be performed to stiffen the patient’s cornea, so as to arrest progression of the disease.
To treat a moderately-protruded cornea, intra-corneal ring segment implantation can be considered. The ring segments mould the cornea into a rounder shape, with the main aim of allowing a better contact lens fitting. If hydrops occurs, eye drops may be prescribed to reduce corneal edema and prevent infection.
In severe cases of Keratoconus, or significant corneal scarring, corneal transplantation (keratoplasty) will be necessary. This can take the form of lamellar (partial-thickness) or penetrating (full-thickness) keratoplasty. A deep lamellar keratoplasty (DALK) preserves the inner-most layer of the patient’s cornea (endothelium), and helps avoid rejection of this critical lining that preserves the optical clarity of the cornea.
Keratoconus enjoys one of the highest success rates among all types of corneal transplantation, but possible complications which include graft rejection, astigmatism, intolerance to contact lens wear and infection can still occur and patients may require long-term follow-up after surgery.
Clinical Associate Professor Heng Wee Jin, Senior Consultant, Head of Cornea & Refractive Surgery (LASIK), Department of Ophthalmology, Tan Tock Seng Hospital, National Healthcare Group Eye Institute.