The use of ill-fitting contact lenses can prematurely age your eyes.

'Wearing ill-fitted lenses not prescribed for you will result in your corneas ageing prematurely,' said Dr Stan Isaacs, president of the Singapore Contact Lens Society and clinical director of I & Vision.
 
So will sleeping with lenses that are not designed for you to do so and using lenses that do not fulfil your oxygen requirements, he added.

Dr Lim Li, a senior consultant ophthalmologist in corneal service at Singapore National Eye Centre, said: 'Corneal ageing is a natural process. However, this can be hastened by the wearing of inappropriate lenses like the use of hydrogel soft contact lenses in those with high myopia.'

The cornea is made up of five layers of tissue, the innermost layer being the endothelium. At birth, the endothelium is made up of a single layer of evenly sized, hexagonal cells that are closely packed together. The endothelium's essential function is to control the state of corneal hydration and to keep the cornea clear.

Dr Isaacs said: 'As endothelial cells age, their size changes and cell density goes down. When we talk about premature corneal ageing, we're saying the cornea is put under unnecessary stress that accelerates these changes.

'It is like getting wrinkles prematurely from exposure to excessive UV rays and lack of sun protection.'

When contact lenses reduce the amount of oxygen going to your cornea, they adversely affect the structure and function of the endothelium. The most obvious changes are that the endothelial cells become larger and more distorted and cell density is reduced. These are closely associated with the onset of a condition known as 'corneal exhaustion syndrome'.

Dr Isaacs said the cornea needs oxygen to maintain its transparency.

While premature corneal ageing will not lead to serious complications like blindness, the condition can cause other problems, such as the patient becoming intolerant to contact lenses or a slowing down of the eye's healing process after corneal surgery.

In the 1960s, hard PMMA (a transparent thermoplastic) contact lenses were introduced in Singapore and such lenses did not allow oxygen to pass through to the cornea.

Dr Roland Izaac, an optometrist and contact lens practitioner in private practice, said: 'People using such lenses did not get enough oxygen in their corneas. After many, many years of use, we started noticing changes to their corneal endotheliums.

'These changes became known to the layman as ageing eyes.'

By the time a patient notices symptoms like red eyes or an uncomfortable feeling while wearing contact lenses, premature corneal ageing would already have occurred and the process is only moderately reversible, Dr Isaacs said.

He advised patients to see a qualified eyecare professional once every six months to have their eyes checked and corneal health assessed.

Nowadays, contact lenses across the board have higher oxygen permeability than their predecessors.

Dr Izaac said: 'The healthier choices include silicone hydrogel lenses, daily disposable lenses and rigid gas permeable lenses.'

Silicone hydrogel lenses transmit higher levels of oxygen than conventional contact lenses and allow as much oxygen as your eyes require.

Rigid gas permeable lenses have high oxygen permeability and there is a lower risk of contact lens-related allergic conjunctivitis and infective corneal ulcers. They are also more suitable for lens wearers with dry eyes, Dr Lim said.

As everyone's eyes and corneas are different, it is imperative that people who want to wear contact lenses have their eyes checked by a qualified eyecare professional before buying or wearing contact lenses.

Dr Isaacs said: 'Everyone's tolerance for the amount of oxygen let in by lenses is different.

'It's important for patients to discuss with their optometrist how long they'll wear lenses for, how disciplined they are and their lifestyle requirements.'