Hyperopic PRK and LASIK

Both PRK and LASIK performed with the Nidek EC-5000 laser appear to be effective in the treatment low hyperopia, according to the results of two studies conducted in the UK and Ireland, respectively..

In the British PRK study, the laser achieved predictable and stable results in the treatment of low hyperopia, but late regression was seen in patients with refractive errors of +4.0 D or more. The study’s results also underscored the importance of treating any pre-existing cylinder in order to avoid inducing further astigmatism, said Stephen J. Doyle, MD, who is in private practice in Manchester, UK.

The Manchester investigation involved 26 eyes in 26 patients with a mean age of 47 years. Their mean pre-operative spherical equivalent was +3.45 D while the mean cylinder value before treatment was +0.33 D. None of the patients had a pre-operative spherical equivalent greater than +4.5 D and only one patient had a cylinder greater than +1.5 D. Dr. Doyle and his associates used a 5.5-mm optical zone and a 9.0-mm blend zone. They did not treat any existing cylinder, as their machine did not have software for hyperopic astigmatism at that time.

Little BCVA Loss

At six months follow-up the mean sphere was 0.77 D and no eyes lost more than one line of BCVA. However there were six cases of late regression, all occurring in eyes with +4.0 D of hyperopia or greater pre-operatively, and in some cases occurring after six months of follow-up.

"Patients were generally very happy. It was interesting that they were more satisfied in the first weeks after surgery than myopes who undergo PRK because suddenly they could read without correction, which they just couldn’t do before.

" However, our main problem is late regression in the higher hyperopes. We’re still not sure how we might prevent this because at three months their appeared to be good stability but then at six months you have these late regressers. You can’t really be giving steroids for six months and we don’t really know if it would make any difference anyway."

Dr. Doyle noted that in common with trials using other lasers, in their study PRK had a tendency to induce astigmatism in patients whose pre-existing stigmatism is left un-treated.

"Our calculations showed that we got 0.3 D of surgically induced astigmatism for every dioptre of pre-operative cylinder. This is more than with myopes and shows the great importance of accurate fixation/centration. It’s a random process, which can either increase or decrease the cylinder you started out with beforehand. We therefore think that you shouldn't treat any hyperopia purely on the spherical side in the presence of more than half a dioptre of astigmatism," he said, concluding:

"We feel that PRK is a good treatment for the low hyperopes. Up to +2.0 D or +3.0 D you are safe and will have very satisfied patients. In higher hyperopes, LASIK works better."

Dr. Doyle’s co-authors in his presentation to the ESCRS Congress in Vienna were E. Hynes, N. Marshall and S. Shah.

Hyperopic LASIK Results From Ireland

The Irish study indicated that LASIK with the Nidek EC-5000produces good, predictable results in the lower ranges of hyperopia. However the laser’s nomograms required adjustment in order to achieve optimal results, said Frank Lavery MD who is in private practice in Dublin, Ireland.

In 46 eyes in 26 patients with hyperopia ranging from +1.5 D to +4.5 D, LASIK treatment reduced the mean sphere equivalent from +2.5 dioptres to a pre-operative a mean of 0.25 D at three months follow-up. They found the best results were achieved when the laser was applied for 22 to 25 seconds per dioptre, he noted.

Prior to the study Dr. Lavery and his associates had used the built-in NIDEK software for the hyperopic ablations. However, as this resulted in over-corrections and under-corrections in many cases they refined their approach by gradually increasing the exposure time and titrating each subsequent group of cases on the basis of the their results, he explained.

The first 14 eyes were treated with an exposure time of 10 and 15 seconds per dioptre, the next 19 eyes with an exposure time of 22 seconds and the final 23 eyes with an exposure time of 25 seconds per dioptre. All of the patients in the first group were "grossly under-corrected" but as the dosage was increased 22 seconds , there was a mean under-correction of 11.5% under-correction. With 25 seconds per dioptre exposure, the mean over-correction was 16.1%.

"There is a dramatic improvement in vision and one starts getting good results in terms of visual acuity from 20 seconds all the way up to 25 seconds treatment. When the treatment is 25 seconds per dioptre results have become more accurate and now produce predictable results in the lower ranges of hyperopia, " Dr. Lavery pointed out. His co-author is A. Cunningham, MD.