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Effect of scleral expansion may be only pseudoaccommodation, surgeon says
An aniridic patient provided a window into the effect of scleral expansion on the crystalline lens.
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VIENNA — Schachar’s theory of accommodation, which suggests that physiological accommodation is due to the stretching of the crystalline lens provoked by tension on the zonules, has its critics. But according to at least one practitioner, there is a genuine effect on the crystalline lens when scleral expansion is applied.
Georges D. Baikoff, MD, a professor of ophthalmology at the Clinic Monticelli in Marseille, France, has been intrigued by the theory of accommodation proposed by Ronald Schachar, MD. However, “I was respectful of the rigor that was taught by my old professors,” he said, referring to Helmholtz’s 1909 theory that accommodation is related to the relaxation of the zonules by the ciliary body. Nonetheless, he plunged himself into the literature. “I found a very interesting article published by Robert S. Wilson in 1997,” said Dr. Baikoff, here at the annual meeting of the European Society of Cataract and Refractive Surgeons. “Wilson had the chance to observe this accommodation on an albino patient.”
Wilson was able to examine the crystalline lens of the 27-year-old woman who had ocular albinism by retro-illumination using an infrared camera. “The behavior of the crystalline diameter was filmed during accommodation and under the effect of different eye drops,” Dr. Baikoff explained. “To ensure the precision of the measurements of the crystalline diameter,” he continued, “Wilson measured the crystalline in pixel units,” electronic units measured on the video screen.
Crystalline diameter changed
Wilson concluded that during natural accommodation, “the crystalline diameter decreases,” Dr. Baikoff noted. However, “when accommodation is blocked, the crystalline diameter increases, and when 2% pilocarpine is dropped in the eye, it causes a pharmacological spasm of accommodation and the crystalline diameter decreases again.” Such observations confirm Helmholtz’s theory, Dr. Baikoff continued, and run contrary to Schachar’s theory.
“But there are published cases where the scleral expansion seems to achieve results of accommodation,” Dr. Baikoff noted. “Is this true or not?”
Recently, Dr. Baikoff had the opportunity to examine under general anesthesia a 1-year-old child with congenital aniridia. He made a video analysis of the behavior of the crystalline lens under a simulation of scleral expansion. These images show, “without a doubt, that scleral expansion increases the zonular tension and that this zonular tension will act on the equator of the crystalline lens,” Dr. Baikoff stated. “By lifting the sclera, it is possible to deform the equator of the crystalline lens and to cause an increase in the crystalline diameter according to the axis of stretching.”
A suture was placed in the sclera of the child, and scleral expansion almost identical to the effect of scleral expansion segments proposed by Schachar was applied.
“You can observe very well that at the moment of expansion, the zonule is stretched and the equator is attracted toward the sclera,” Dr. Baikoff said. “There is a peripheral flattening of the crystalline lens and an increasing steepening of the convexity of its central part.” Consequently, there is the potential “to modify, by an artificial method, the curvature of the crystalline lens and maybe even its optical power.”
Validation of theory
Dr. Baikoff noted that “I really believe that the theory of Helmholtz is true because it was proven in a definitive way by Wilson that at the moment of accommodation, the crystalline diameter decreases and that it increases when accommodation is relaxed.”
In contrast, his study of the aniridic child “proves that a scleral expansion can deform the crystalline lens and perhaps modify its optical power.”
For Your Information:
- Georges D. Baikoff, MD, can be reached at Centre D’ophtalmologie-Clinic Monticelli, 88 rue du Commandant Rolland, 13008 Marseille, France; (33) 4-91-162-228; fax: (33) 4-91-162-225. Dr. Baikoff did not participate in the preparation of this article.