Soft contact lenses or hard contact lenses?

Contact lenses are a very popular form of vision correction. In Singapore, it is estimated that 600000 people wear them (ST, Sep 1 2012 'Contact lenses safe, provided proper care is taken'), with a very low risk of complications.

Generally, contact lenses can be divided into soft and hard varieties. Soft lenses tend to be large in diameter and are flexible, so they can be folded. They are much more comfortable to wear, and currently the most commonly used ones are of the disposable type. Although soft contact lenses first became available in 1971, the disposable type only became available from 1987 onwards.

Nowadays, there are daily disposable, 2 weekly disposable, and monthly disposable types. And of course, there are the longer term, permanent lenses which actually are used for about 1 year before they need to be replaced. Daily disposable lenses are expensive, but they are least likely among soft contact lenses to cause problems such as allergies or infections, unless the user does not wear them according to instructions. Daily disposable lenses also are thinner, and so less likely to cause or exacerbate dry eye situations. Even 2 weekly or monthly disposable types are worn successfully by many people, and are most cost efficient for those who wear lenses on a daily basis.

Current 'hard' or 'semi-hard' lenses usually refer to corneal rigid gas permeable lenses (RGP), and these were first introduced in 1978. In actual fact there are other types of hard lenses, such as scleral lenses, and there are even hybrid hard lenses with a soft skirt at the edge, but these are more rarely used.

In 2012, RGP lenses made up 9% of contact lenses worn in the US. Source: Contact Lens Spectrum, January 2013. 

They are less widely used than soft lenses, because there is an initial period when RGP wearers will feel the lens in their eye. This uncomfortable sensation is akin to having an eyelash in the eye-ie it is not very painful but in the initial stages can cause tearing and bother the wearer. Once over this period (up to 2-3 weeks), the lens is as comfortable as soft lenses, and the RGP lens really begins to shine. Occasionally, if a bit of dust gets under the contact lens, that can cause eye pain, but a quick rinse with even tap water will clear this easily.

The benefits of RGP lens wear are many, among which are sharp vision (usually sharper than soft contact lenses or spectacles), very good oxygen permeability (yes, your cornea needs to breathe oxygen in the air!), less tendency to be affected by dry eyes, and very good durability.

One reason why some young children used to be started on RGP lenses was a belief that wearing them could slow the progression of shortsightedness (Myopia). However, a study done 10 years ago (Arch Ophthalmol. 2004;122(12):1760-1766) showed that there was no difference in growth of eyeball length between the soft contact lens wearers vs the RGP lens wearers. This suggests that RGP lenses have no real ability to  retard the progression of shortsightedness.

There is a special class of RGP lenses called orthokeratology lenses which are worn to sleep, and are worn with the intention to flatten an area of the cornea. I will cover these lenses in a future post as they are used in a radically different way compared to other contact lenses.

Should one go for soft lenses or hard lenses? I would say that for the majority of people, soft contact lenses are best because of the comfort, ease of wear and care. They are good for occasional wearers and those with otherwise healthy eyes.

RGP lenses would be especially useful for those with the desire or need to see with very sharp vision, and those for whom the extra thickness of soft contact lenses might give rise to problems eg those with very high spectacle power, or those with dry eyes.

I guess I am partial to RGP lenses, having worn them myself for over 30 years. The only thing I avoid doing with any regularity is swimming, even though it is possible to wear goggles with them on. I have gotten so used to them that I actually find it easier to wear them than soft contact lenses.