Common operation can remove important antioxidant and jeopardise eye health, say scientists.
Auckland University researchers are warning that eye surgery to replace a cloudy lens may not be as safe as was thought.
Eye scientist Dr Julie Lim and PhD student Ankita Umapathy have discovered important details about an antioxidant substance that is produced in the part of the eye that is removed by cataract surgery.
Cataract refers to a cloudy lens. The lens sits behind the coloured iris near the front of the eye. A degree of cataract is a normal part of ageing although the condition can have other causes, including diabetes. Once the cloudiness affects vision too much, the lens can be replaced with a plastic one. Cataract surgery has traditionally been considered safe and effective. The operation is sometimes done for other reasons, including extreme short-sightedness, and this is called lens replacement surgery.
In New Zealand, 14,226 patients had publicly funded cataract surgery last year, the National Health Board said.
Dr Lim and her student are studying an antioxidant called glutathione. Antioxidants can neutralise so-called free radicals.
"In terms of the lens," Dr Lim said, "if you have excess free radicals they can damage protein, causing them to aggregate and form a cataract."
Glutathione is present throughout the body and the lens has the greatest concentration of the substance.
"At the moment we're just doing basic science experiments and it hasn't been published yet, but my PhD student has shown that the lens can actually export glutathione and that the cornea and [two other structures in the eye] contain uptake pathways for taking up glutathione."
The next step is to do more experiments to prove that glutathione is used by these structures in the eye, one of which, the ciliary body, secretes the fluid that surrounds the lens and cornea and has an important role in setting the pressure level within the eye.
If these structures use glutathione and are deprived of it by the removal of the lens, the eye may be at increased risk of corneal cloudiness and the condition called glaucoma, which is caused by increased pressure in the eye. Both diseases can cause blindness.
"I don't want to scare people away from cataract surgery," Dr Lim said.
"There is growing evidence that persistent damage to tissues of the eye can occur several years after the removal of the lens during cataract surgery."
This might become more marked because of population ageing and the increasing prevalence of diabetes leading to a rising number of cataract operations, in addition to the "clear lens exchange" surgeries, she said.
Increased life expectancy meant there was a longer time after surgery in which eye damage could occur from lack of glutathione in the eye.
"Providing an extra source of [glutathione, through eye drops] after cataract surgery may provide a long-term solution to maintaining eye health in the elderly."
* Glutathione is a protective antioxidant present in the lens of the eye.
* It is sent to other parts of the eye.
* Cataract surgery removes the lens.
* This may deprive the eye of glutathione and increase risks of other eye disease.