Degenerative eye disease now has cure

PUBLISHED : Tuesday, 28 August, 2012, 12:00am
UPDATED : Tuesday, 28 August, 2012, 6:11pm

As the mother of an adorable year-old girl, Lau Mei-fong was accustomed to some of the common perils of parenthood, such as being often blurry-eyed from broken sleep. But Lau, 30, began to notice that her vision was discomfortingly fuzzy more often.

Oddly, the lower part of her vision would be more distorted than the rest. So, when she read, the bottom of letters would be blurry while the rest would remain relatively in focus.

Lau (whose name has been changed for patient confidentiality reasons) had been shortsighted for a good part of her life. But while the vision of most people with shortsightedness stabilises in adulthood, Lau's continued to worsen in her 20s.

In fact, she had to visit her optometrist more frequently in recent years to change her contact lenses. One day, the optometrist refused to change them and referred her to Dr Arthur Cheng Chak-kwan, a specialist in ophthalmology at the Hong Kong Sanatorium and Hospital.

The optometrist told Lau that she might have a condition called keratoconus, which corrective lenses could not help. Lau went home to research the condition online before her appointment with Cheng.

What she found gripped her with fear. Keratoconus is a degenerative eye condition affecting the cornea, a clear tissue covering the front of the eye that protects the eyes, filters out some of the sun's ultraviolet rays and bends light entering the eye to help us see.

While a normal cornea has a round shape, a cornea afflicted by keratoconus becomes increasingly thin and cone-shaped. It becomes incapable of focusing light on a single point and and the patient's eyesight becomes increasingly fuzzy, starting from the periphery.

Corrective lenses cannot refract light far enough to compensate for the cone-shaped cornea and normal soft contact lenses will not be able to sit on the deformed cornea.

In the past, there was no treatment to halt the progression of keratoconus, leaving patients with a rather dismal prognosis. So Lau was very concerned.

But when she met with Cheng, he assured her that if she had keratoconus there were a number of treatment options available. More importantly, she would keep her sight.

Cheng explained that the cornea is made of multiple layers of tissue held together by a chemical bond, rather like glue, called crosslinking. In patients with keratoconus, the crosslinking is weak and the cornea is more pliable than in normal people.

Doctors suspect that people who develop keratoconus are born with the condition, or at least have a greater propensity to contract it. Many patients also have allergies, resulting in them rubbing their itchy eyes.

The mechanical action of rubbing the already weakened cornea further stresses the damaged layers of corneal tissue, causing them to slip and slide against each other, thereby distorting the hemisphere shape of the cornea.

Lau's was a classic case - she had suffered allergies for 10 years and had a habit of vigorously rubbing her eyes to relieve the itch. The onset of her visual problems, in her 20s, was also a strong indication of keratoconus. Most other corneal diseases show up when patients are in her 50s or 60s.

Moreover, Lau had recently had a baby. Doctors think that pregnancy can worsen keratoconus because hormones are released to help soften tissues to prepare the body for childbearing and childbirth. These same hormones may further weaken the crosslinking between corneal layers.

To confirm his suspicions, Cheng mapped the topography of Lau's cornea using a non-invasive imaging device. He found that Lau did have the condition and, like most patients, there was more distortion in one eye than the other. Her right eye was at a moderate stage, while the left eye was in the early stages of keratoconus.

While the existing damage was irreversible, Cheng proposed that Lau undergo a procedure called collagen crosslinking to halt the progression of the disease.

During the 30-minute surgery, Lau's eyes were bathed in a special vitamin B solution while being exposed to ultraviolet light. Ultraviolet light and vitamin B react to strengthen the cross- linking collagen in the corneal layers.

A month after the procedure, Lau returned to have special hybrid contact lenses fitted. The hybrid lens is hard in the centre to cover the irregularities of the cornea and present a smooth surface to bend light. A soft edge makes it comfortable.

The corneal crosslinking procedure has a 90 per cent success rate. In the remaining 10 per cent, repeating the procedure usually works.

The treatment was only invented a decade ago, so there is no data on the risk of further keratoconus degeneration later in life. But the available data indicates the positive effects of the treatment are long term.

Even if the effects of collagen crosslinking do not hold, patients who suffer more severe corneal distortion can use an intracorneal ring to push down the cornea to help it hold a more spherical shape. This way, the hybrid lens can sit on the cornea.

For those patients in advanced stages of the disease, hope of a cure lies in a corneal transplant, says Cheng.


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