Article Date: 4/1/2002

readers' forum
Myopia Control and Contact Lenses
BY ROBERT J. MORRISON, OD, FAAO

In his article, "Rigid Contact Lenses and Myopia Progression," (November 2001), Jeffrey J. Walline, OD, MS, pointed out that my paper was the first to report the possible value of using a rigid contact lens as a contact lens as a therapeutic device in attempting to control the progression of myopia. He further acknowledged subsequent studies by Black-Kelley, Stone, Grosevnor and Khoo, all of which found some value in limiting the progression of myopia through wearing rigid lenses.

In our practice and in the optometry and medical schools where I teach, we have always advised, and continue to advise, all parents that this was an observation, and one that has not been subjected to the rigid classic control groups usually required to establish a recognized theory. I was indeed pleased and relieved when the first magazine (Time, 1957) began the article with "In a cautious preliminary report, Dr. Morrison..."

Initial Observations

My initial report was on a wide range of children and young adults (ages 7 to 19) and reported that need of additional minus power in the contact lens was not required in the first year and a half of wear. It did not report on the spectacle power required for refractive correction when the contact lenses were not worn for some days or weeks.

I fit the children in my study with PMMA lenses with base curves that were flatter than the flattest ophthalmometer reading. Some did show mire distortion after weeks of wear.

I thought that since 24 percent of the world (60 percent of Asians) is myopic, I should share this observation with my colleagues. I am pleased there are over 20 myopia studies currently funded by the National Eye Institute. Hopefully, we will learn if we have the moral right to recommend rigid or soft contact lenses for children and adolescents with myopia.

Possible Explanations

Dr. Walline mentioned in his article that I "reported some observations to the American Academy of Optometry." I did list a number of possible reasons for this phenomenon and did so again at the meetings of the British Contact Lens Society and the Belgian Ophthalmology Society. Since a number of Contact Lens Spectrum readers have asked that I repeat these reasons reported at the three meetings mentioned above, I have listed them:

1. Because the average person blinks 20,000 to 25,000 times per day, the rubbing effect may be a factor

2. Because we had a strong desire to see that the youngster had good vision, we may have "over minused"

3. If indeed Number 2 is true, a smaller pupil allowing better depth of focus, less desire for minus power, may have occurred

4. The lenses were fitted flatter than the flattest reading obtained by the ophthalmometer (flatter than the flattest K reading), resulting in a slightly flatter front refracting surface.

5. The absence of spectacles (usually perched on the nose about 10mm to 15mm in front of the cornea)

6. The contact lens is closer to the nodal point of the optical system of the eye. A better optical system, perhaps less strain

7. Spectacles present spherical and other aberrations

8. The absence of induced base in prism as the spectacle wearer reads

9. The possibility of spectacle-induced phorias

10. The comfortable contact lens wearer often wears the contact lens all day; the spectacle wearer may wear them for only part of the day

11. A change, perhaps chemical, to the precorneal (tear) film. Possibly a different index of refraction, different pH, etc.

12. Less oxygen reaches the eye (although the cornea must be carefully monitored for edema). The effect, if any, on refractive power needed is unknown.

13. Because the contact lens is fitted flat, and since most flat fitted lenses position superiorly, the thicker portion of the minus lens may be positioned over the pupil, causing a slight overcorrection.

14. Some factor, perhaps one of the above, perhaps a support effect, may affect axial length. (Most myopia is believed to be axial, where the cornea protrudes, and if the axial length of the eye is longer, myopia almost always is present)

15. Many youngsters found new confidence, read less and took part in other activities they might have avoided when wearing spectacles. (Some patients even reported poorer grades in school as the patient read less, studied less, and took part in other activities since wearing contact lenses)

16. Uncorrected astigmatism may be present. When soliciting a patient's subjective response, the far end of the interval of Sturm may have been selected; an overcorrection might ensue.

Dr. Walline's Response

I was honored to see a response to my article from Dr. Morrison. I attribute the observation that Dr. Morrison made to the creation of the idea that rigid contact lenses may slow myopia progression in children. Even today, many practitioners are cautious about fitting young children with contact lenses, but Dr. Morrison realized long ago children's potential for maturity and responsibility in contact lens care.

I often criticize Dr. Morrison's report because it did not include a control group, the children were older than the age we expect for myopia progression and because the contact lenses were fitted flatter than the flat corneal curvature. However, I realize that his work reported the first observation and was not designed to study the effect of the contact lenses. Thankfully we will be able to examine some of the variables Dr. Morrison suggested that may have influenced the results of his study, such as axial growth of the eye, heterophoria and corneal edema.

I would like to take this opportunity to publicly thank Dr. Morrison for beginning the study that I hope to conclude, and to congratulate him on an astute observation that has the potential to change the current standard of care for myopic children.

Things to Consider

When I was privileged to be co-patent holder for all soft contact lenses in the Western Hemisphere, and some other countries, we fit many myopic children with hydrophilic gel lenses. Unfortunately, we focused on learning how to manufacture, fit and work with this new paradigm and not on myopia control. We did observe that some wearers needed more minus power for correction when studied at later dates. We observed this same finding with rigid gas permeable lenses, but less so, with either lens material, than with spectacles. We felt the RGP material showed less need for additional minus power than the soft material.

I would like to respectfully suggest to those studying this possible controlling effect to differentiate between the amount of minus power prescribed to afford a contact lens correction and the amount of myopia present.

I also suggest that some of the possible reasons I listed above be studied concerning their possible relevancy, for example the chemistry of the tears, axial length of the eye, phoria changes induced, presence of non-symptomatic edema and importance of early and ongoing history.

Dr. Morrison is clinical professor of ophthalmology at Pennsylvania State University College of Medicine in Hershey, PA.

 


Contact Lens Spectrum, Issue: April 2002