Scleral expansion bands still rooted in controversy

One surgeon believes improvements can only be minimal, inconsistent and temporary; another suggests a modified technique might be the key.

ByMichela Cimberle

CEDEX, France — Presbyopia still represents the most difficult refractive problem to treat, and as the population ages, the demand for new, effective procedures is constantly increasing. Among other options, scleral expansion bands were shown to be still controversial.

According to François J. Malecaze, MD, the scleral expansion bands (SEBs) of Schachar opened the door to a new approach to presbyopia, but the outcomes of SEBs to date are inadequate to propose them as a treatment.

“Improvement is minimal, inconsistent and temporary,” he said, adding that he is personally pessimistic about the future of this technique.

Disappointing results

Dr. Malecaze implanted SEBs in eight eyes of patients ranging from 49 to 63 years of age.

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Baïkoff wedge effect: On the contrary an optimized shaped deep supraciliary segment exerts an inward force assisting the failing contraction of an aging ciliary body. In addition, a very deep insertion prevents the risk of extrusion and allows a much more stable effect.

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Schachar’s effect: A superficial expansion segment is bound to expel because of the centifugal force exerted on the sclera, which provokes a cheese wiring effect on this tissue. Such an action must be transitory.

“We used the three successive generations of subscleral expansion bands. They were well tolerated: no conjunctival redness, no uveitis, no modification of far vision were observed. IOP and pupil size were unchanged after surgery,” he said.

“But is the technique effective?” he asked. “When the study was performed there was no clinically available objective method to evaluate accommodation. So we performed a series of subjective tests, taking extreme care to eliminate bias.”

Accommodation was evaluated using retroilluminated reading charts, under the same conditions of luminance, calculating the reading distance with the graduated ruler and using triplicate measurements. Near vision was measured at 40 cm and 60 cm with and without addition, using also the push-up and push-down methods and the minus lens procedure. Mean follow-up of patients was 1 year.

One month after surgery, improvement of near vision was observed in three eyes. However, at 3 months the effect of the scleral bands had faded, and patients were back to preoperative values. These results were confirmed by the push-up and push-down methods. There was no improvement at all in the other five eyes.

“Our results are in accordance with those of other studies, and they appear inadequate to support the use of this treatment,” Dr. Malecaze said.

Unclear mechanism

The mechanism behind the temporary improvement of some eyes that undergo this surgery is still unclear.

“The problem is that, despite the new technological means of investigation, like Scheimpflug camera, UBM and magnetic resonance imaging, we still don’t know much about the mechanism of accommodation and consequently about presbyopia,” Dr. Malecaze said.

The classical theory of Helmholtz is still the most widely accepted: during accommodation the ciliary muscle contracts and the lens, which is elastic, becomes rounder. However, not all the authors agree on the reason why the eye becomes presbyopic with age. Some attribute the main responsibility to the lens, some to the ciliary muscle, others to both of them.

Schachar’s surgical technique is based on the assumption that presbyopia is caused by the continued growth of the lens, which reduces the distance between the lens equator and the ciliary muscle and therefore causes relaxation of the zonule. By inserting SEBs, the surgeon should be able to increase the distance between the muscle and the lens, thus increasing zonular tension and allowing the accommodative system to work again.

“Personally, after my experience, I believe the main mechanism of presbyopia is that the lens becomes harder and loses elasticity with age. If this is true, there is not much you can do to restore accommodation. My feeling is that Schachar’s technique may work for some weeks or months, if it does, only in young presbyopic patients between 45 and 55 years. After this age the lens is too hard to respond effectively to whatever solicitation,” Dr. Malecaze said.

Potential improvements to this method, like modifying the geometry of the SEBs or their position, may perhaps increase the lifting effect, but do not appear to lead to more long-lasting results.

Need for objective methods

A major problem in finding new surgical solutions for presbyopia lies in the fact that any new technique needs to be experimented in animals. Dr. Malecaze noted that animals “don’t read, or they don’t tell you if they read or not.”

For this reason, it is important to find objective methods for measuring visual outcomes, and several companies are already working on it, he said.

Different point of view

An entirely different point of view on the same matter was proposed by George Baïkoff, MD. He also conducted a trial using personally modified scleral expansion bands and Schachar’s surgical technique.

Comparison of theories

Helmholtz theory

In distant vision the ciliary muscle is relaxed and the zonules of the lens are under tension. When the eye accommodates, the muscle contracts, reducing the tension on the zonules. This reduced tension allows the elastic capsule of the lens to contract, causing a decrease in equatorial diameter; a decrease in radii of curvatures of the anterior and the posterior surfaces of the lens; and an increase in central thickness.

Presbyopia results from the hardening and loss of elasticity of the lens with age. In the process of accommodation, although the ciliary muscle contracts and the zonules are relaxed, the lens does not change its shape. Therefore, presbyopia is an aging process that could only be reversed by changing the elasticity of the lens or its capsule.

Schachar theory

In the accommodation process, the equatorial displacement of the crystalline lens occurs as a result of increased tension on the equatorial zonules, produced by contraction of the anterior radial muscle fibers of the ciliary muscle. Because an active force is involved in accommodation, the amount of force that the ciliary muscle can apply is dependent on how much the ciliary muscle is stretched.

The crystalline lens is of ectodermal origin and continues to grow throughout life. Except for the progressive myope, the dimensions of the scleral shell do not change significantly after 13 years. The distance between the ciliary muscle and the equator of the lens decreases throughout life. Therefore, the effective force that the ciliary muscle can apply to the lens equator is reduced in a linear fashion with age. The amplitude of accommodation decreases linearly with age, resulting in presbyopia, and is a consequence of normal lens growth.

“First, it is interesting to observe that Schachar’s technique does indeed have an effect on near vision, as the patients operated on had almost normal near vision in the few days following surgery,” Dr. Baïkoff said.

However, in time the results were disappointing, as the positive effects obtained in most of his patients decreased after a few months.

“This confirms it is possible to obtain a ‘Schachar effect’ despite the fact that Schachar’s theory on accommodation seems to be somewhat artificial,” he said.

“I went back to studying the anatomy of this part of the eye and came to the conclusion that, in time, Schachar’s segments would be more than likely expelled because of the centrifugal force,” Dr. Baïkoff said. “On the other hand, going back over the whole theory and physiology of accommodation, it is clear that Schachar’s theory on accommodation is purely theoretical. It is indeed based on a gross misinterpretation.

“It is also possible to bring a completely different solution to the problem that consists of facilitating the normal physiology of accommodation, ie, by pushing the ciliary body inward and forward by using supraciliary segments inserted deeply into the sclera to produce a wedge effect.

“The position of these wedges will modify the anatomical relationship among the ciliary body, the zonules and the crystalline lens, and help release zonular tension. When accommodation is deficient, this wedge will assist the ciliary body and help the lens become rounder and able to move again.”

Understanding the anatomy

“If we look at the anatomy, we can see that zonular plexus is a junction between the posterior and the anterior zonule,” Dr. Baïkoff explained. “The zonular plexus is linked to the ciliary processes. During accommodation there is a contraction and a shortening of the ciliary body and a displacement of the zonular plexus inward and forward.

“If you implant the segment deep in the sclera, you create a pressure that pushes the ciliary muscle inward and forward, modifies the position of the ciliary processes and the location of the zonular plexus, releases the tension of the zonule and provokes a deformation of the crystalline lens. I strongly believe that if there is a chance to obtain a durable effect with segments, it must be done this way. If you modify the anatomy, you won’t exactly restore, but at least assist some residual accommodation.”

In his opinion, although it is unquestionable that with age there is a hardening of the lens, some elasticity is retained and patients around 60 to 70 years old still have a lens soft enough to be able to modify its shape.

“The natural configuration of the lens is and remains spherical. When it is extracted from the eye, it is in fact rounder quite independent of age,” Dr. Baïkoff said.

By using this modified technique of supraciliary segments, Dr. Baïkoff obtained encouraging results, which were stable after 1 year of follow-up.

For Your Information:

François J. Malecaze, MD, can be reached at Service Ophthalmologie, Hôpital Purpan, Place Dr. Baylac, 31059 Toulouse Cedex, France; +(33) 5-61-77-74-04; fax: +(33) 5-61-77-24-45; e-mail: malecaze.fr@chu-toulouse.fr.

Georges Baïkoff, MD, can be reached at Centre D’Ophtalmologie Clinique Monticelli, 88 rue du Commandant Rolland, 13008 Marseille, +(33) 49-116-2223; fax: +(33) 49-116-2225; e-mail: g.baik.opht@wanadoo.fr.