BY JOHN MOUNTFORD,
DIP. APP. SC, FAAO, FCLSA
is a rapidly changing science. The procedure is primarily aimed at treating the
myopic population, but newer designs also allow us to use these lenses to treat
hyperopia. From a historical historical
perspective, George Jessen stated in his original lecture on "orthofocus" that hyperopia
responded better to treatment than did myopia because of the edema he induced with
a PMMA De Carle bifocal.
We can't induce excessive edema with overnight wear, so a
different approach is necessary. Jerry Legerton, OD, MS, MBA, FAAO, is adapting
the sigmoid proximity curve on the Paragon CRT lens, while Dr. Tung is using spherical
curves with the Vipok design. In Australia, we're working on multi-aspheric designs.
Figure 1. Pre-fit, post-wear and difference
Figure 2. Fluorescein pattern with pooling
in central area.
Although we're in the early days as far as ortho-k for hyperopia
is concerned, the results look promising. The following case history is a good example.
The Unhappy Hyperope
A 63-year-old female presented with a history of LASIK for hyperopia
that had initially been successful, but the effect "wore off" over the following
six months to where her refraction and vision changed to OD +1.75 –1.25 x
50 (20/30), OS +1.25 –0.75 x 25 (20/25). She was dissatisfied with her unaided
vision (20/60 OU) and also with her corrected vision. The rest of her ocular examination
was unremarkable with the exception of mild dry eye. We asked her to take part in
a trial of overnight orthokeratology for the correction of hyperopia.
fit her with bi-aspheric Boston XO (B&L) trial lenses approximately 2.50D steeper
than K in both eyes. Following one night of overnight wear, we found no clinical
signs of edema or staining and a mild reduction (0.50D) in her refraction. We dispensed
the trial lenses to wear for 10 nights and scheduled her to come in for evaluation
within two hours of lens removal following the tenth night.
The Happy Hyperope
The patient presented with a big smile and reported excellent
vision, "as though the fog had been lifted." Unaided VA was OD 20/20 and OS 20/15,
with a refraction of OD +0.25 –0.75 x 30 and OS +0.25 –0. 25 x 20. Biomicroscopy
Figure 1 shows the pre-fit, post-wear and difference maps. Note
the irregular astigmatism in the pre-fit plot and the central steepening of 1.50D
post wear, as well as the reduction in astigmatism.
Figure 2 shows the fluorescein pattern. Hyperopic lenses work
in the opposite direction to myopic ortho-k lenses in that the central area is fit
steep and the paracentral area has an annulus of compression. The peripheral zone
still controls centration.
The patient originally intended to suspend lens wear after a few
weeks while on an overseas trip, but she was so delighted that she asked me if she
could take them with her on vacation, as she could not stand the thought of looking
through the fog again. How could I refuse?
Dr. Mountford is an optometrist
in private practice specializing in advanced contact lenses for keratoconus,
post refractive surgery and pediatric aphakia. He is a visiting contact lens lecturer
to QUT and UNSW, Australia.
Contact Lens Spectrum, Issue: September 2005