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Laser Cataract

Higher Amounts Of Myopia

Cataract surgery has the added benefit of allowing patients with myopia to have their working distance improved. The two most common outcomes for such patients are that they remain short-sighted or are made more emmetropic and have their uncorrected distance vision improved. It is important, however, to point out that there is some variation between patients and their experience for a given refractive outcome.

Patients who choose to remain short-sighted have typically become accustomed to having clear near vision without corrective lenses, something that being short sighted affords them. They choose to keep their best uncorrected vision at this short distance and are therefore able to read in most situations without glasses. There may be the occasional situation where a weak pair of reading glasses is required to read a number in the telephone book or thread a needle in low illumination. In most situations, however, they will be able to read without glasses.

Their existing dependence on corrective lenses for distance viewing will remain.

Other patients who are myopic elect to improve their distance vision without glasses. Post-operatively they are able to view most distance objects without correction, however, they require glasses for near viewing. Most patients with myopia do prefer to retain a small amount of short-sightedness following their surgery. Keeping a small amount of residual short-sightedness allows them to still achieve some vision in the intermediate range without correction. Objects that are typically viewed in the intermediate range are a price on a shelf in a supermarket, a large font on a computer screen or someone’s face across a small table. With increasing age, more of the typical day is taken up with visual tasks at this intermediate range. On the other hand, with increasing age, the necessity to see objects in the very distance becomes less. Visual tasks at this distance include driving a car, watching a television across the room or watching night sport. It can be a potential source of disappointment for a patient, particularly one with myopia, to lose their uncorrected vision in this intermediate range.

It is therefore important, in most cases, that a myopic patient who desires distance vision without correction retains a small amount of myopia to allow some uncorrected intermediate range vision.

Most patients with myopia are delighted with the reduced glasses dependence this surgery allows them. However, a couple of other issues that may limit their ultimate satisfaction also need to be considered.

As discussed earlier, there are limits to the accuracy of achieving a particular amount of short-sightedness following cataract surgery. Even with modern technology and particular attention to the quality of biometry performed pre-operatively, the final outcome is still within a predetermined range. Most patients with myopia accept some deviation from the prediction, given their increased independence from corrective lenses.

Some patients with myopia are very particular about the distance from their face that they like to perform certain near or intermediate range tasks. Even where the final prediction is achieved very accurately, their ultimate satisfaction with uncorrected vision at this preferred distance can never be guaranteed. It may also not be possible to be certain what this preferred distance is until they have completed their cataract surgery and follow-up to achieve the final visual result. For example, their low-degree, post-operative myopia may result in their best uncorrected vision being at 90cm and their preference is to view a computer screen at 80cm. Again, patients who are highly myopic generally prefer to not have their myopia eliminated completely.

The risk of retinal detachment increases in all patients in the year or two following cataract surgery.  Short-sighted patients have an increased lifetime risk of retinal detachment when compared with non-short sighted patients. This risk is further increased post-operatively. A retinal examination is performed prior to cataract surgery to identify any specific predisposing retinal changes. If found, it is recommended these are treated. Even where this examination does not identify any changes, the post-operative risk is still increased. When a retinal detachment occurs, it requires surgery.

Patients who have undergone laser vision correction have typically enjoyed the benefits that this procedure offers in terms of reduced dependence on glasses for day-to-day activities. They have demonstrated their high motivation to reduce that dependence and enjoyed this benefit, in most cases, for many years.

When those patients subsequently undergo cataract surgery that history of prior laser vision correction needs to be addressed: in particular, the assumptions made about the condition of the cornea in biometry and the process used to determine the required power of the IOL to be implanted after removal of the cataract. This is because the accuracy of the refractive outcome is reduced slightly when compared with the outcome in patients with no history of laser vision correction. This has implications for their future day-to-day glasses requirement.

Numerous techniques exist to determine IOL power in this scenario. Our clinic has the state-of-the-art equivalent K feature of the Pentacam corneal topographer to optimise the accuracy of this refractive outcome.

Consequently, those situations where a patient requires glasses will change. There is also the small possibility that glasses dependence will increase.

With patients who have had their laser vision correction to address short-sightedness, their eye still has the same increased risk of retinal detachment in the year or two following surgery as a patient who has never been short-sighted.

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