An enemy within

PUBLISHED : Tuesday, 12 June, 2012, 12:00am
UPDATED : Tuesday, 12 June, 2012, 12:00am


Sophia Lau, 40, tried to ignore a little bump that was growing on her right upper eyelid, along her lash line. Lau (whose name has been changed for patient confidentiality reasons) thought it was a stye and hoped it would go away on its own.

Many styes, which are much like pimples, do disappear eventually. But Lau's continued to grow in size and discomfort. Eventually, she could not take the pain and discomfort any longer - the growth was now 5mm in diameter - and she turned to Dr Arthur Cheng Chak-kwan, a specialist in ophthalmology at the Hong Kong Sanatorium and Hospital, for help.

Cheng saw that the stye had become a chalazion, where the inflamed oil gland had become fully blocked and infected. The collection of pus inside the cyst was too much for antibiotics alone to resolve. He had to make an incision to drain the pus and deflate the chalazion. He then gave Lau antibiotic eye drops for day use and an antibiotic ointment for the nighttime.

By the end of the week's course of antibiotics, Lau's eyelid was good as new. But several weeks later, she noticed another little bump emerging on the lower lid. Having learned her lesson with the first stye, Lau made a beeline for Cheng's office.

Cheng was puzzled at the recurrence of the stye. It was evident that the medications were effective in clearing out the stye-causing bacteria. But it was rather unusual for another stye to develop in a different location on the same eye. Nevertheless, Cheng prescribed another course of medication.

Lau was relieved when the bump shrivelled up and disappeared in days. But, again, another popped up a few weeks later, this time on the upper lid of her left eye.

This time, despite the antibiotics Cheng prescribed, the stye continued to grow. Cheng had to repeat the drainage procedure when the chalazion ballooned to 5mm.

Although there was nothing in Lau's reported medical history or personal habits that could explain the persistent appearance of styes, Cheng knew something else was afoot. He mined the medical journals and papers for possible explanations for Lau's condition. He finally struck gold.

Cheng noticed that a parasitic mite called Demodex was sometimes associated with blepharitis, a condition in which eyelash follicles get inflamed. People who have suffered blepharitis are more prone to repeated styes and chalazia. Lau did not have the condition, but Cheng wondered if Demodex might also be involved in Lau's unusual case.

While there are some 65 species of the eight-legged arthropod, only two species are found on humans: Demodex folliculorum and Demodex brevis. They are commonly known as eyelash mites, and they feast on the natural oils, or sebum, produced by skin. These microscopic parasites have a life cycle of 14 to 18 days.

Up to a quarter of the population, especially adults, might have some Demodex mites living harmlessly on their skin and eyelashes. Problems occur when there is an overgrowth of mites.

Cheng conferred with his colleague Dr Bone Tang Siu-fai, a specialist in clinical microbiology and infection. Tang helped with the testing and identification of this parasite, as there was no standard laboratory protocol in place.

Because the mites are nocturnal creatures, in the daytime they burrow into the eyelash follicles. Sample eyelashes had to be plucked and immediately placed in saline to keep any mites present alive. Cheng took four eyelashes from each of Lau's eyes.

Under a microscope, the doctors found live Demodex folliculorum mites wriggling away on the samples.

While the mites do not necessarily cause infections, they can plug the opening of glands that produce the protective oily substance in the eye, says Tang. Their scaly surface traps infection-causing bacteria, resulting in styes and chalazia, adds Cheng. Demodex infestations can also cause red, itchy, dry and irritated eyes.

With the culprits pinned down, the next step was to eradicate them. Only two substances appeared effective: 100 per cent alcohol and tea tree oil solution. But alcohol was not an option because the high concentration of the solution could damage the eye.

Cheng did a skin test to ensure that Lau was not allergic to tea tree oil. Next, the doctor protected her cornea surfaces with contact lenses and applied local anaesthesia to her eyes.

He then applied a solution of 50 per cent tea tree oil and 50 per cent paraffin oil to her eyelashes.

Five to 10 minutes later, he cleaned the lashes again, and repeated the procedure.

Despite the protective measures taken, Lau still felt a stinging sensation in her eyes. Hence, it is imperative that such a treatment is done by a qualified doctor.

Lau needed to repeat the tea tree oil treatment another two times. Cheng said the first application of the tea tree oil would draw the mites out from their hiding places at the base of the eyelash follicles.

The second and third tea tree oil treatments would ensure that the mite population was largely exterminated.

When she returned home, Lau was advised to wash her face, eyebrows and hair with tea tree oil shampoo.

She also had to wash her pillow case, bed sheets and linen in boiling water to clear out any stragglers in the mite population.

After Lau's case, Cheng saw an inexplicable and unusual spate of about 30 similar cases.

Subsequently, the doctors developed a protocol for patients presenting with styes and chalazia to be automatically tested for Demodex infestations.

Tang also taught the nurses and laboratory technicians how to retrieve and prepare the eyelash samples for investigation.