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Anterior ciliary sclerotomy promising for treating presbyopia
More than 200 cases of ACS with tissue barriers in the incisions have been followed for 2 years with good retention of restored accommodation.
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Restoration of accommodation through the surgical correction of presbyopia has become the new frontier of refractive surgery. The baby-boom generation currently makes up more than 30% of the U.S. population, and it is estimated that new cases of symptomatic presbyopia – that is, cases that require reading glasses or bifocals – approach 3 million per year in the United States alone.
Recent studies suggest that it may be time to consider the scleral approach to presbyopia treatment with anterior ciliary sclerotomy (ACS) with tissue barriers in the incisions to retain scleral expansion. These barriers, manufactured by Surgical Specialties Inc., are inserted into the incisions created during ACS to maintain the expansion of the globe.
| Ciliary sclerotomy: Incisions begin at the limbus, crossing into the sclera and carried 3 mm over the ciliary body to stop just short of the pars plana. Crowned zonules may contribute to presbyopia. Images: Thornton SP |
Understanding ACS
Because of continued growth of the lens, the distance between the ciliary muscle and the lens equator decreases throughout life, reducing the effective force of the ciliary body-zonule complex, resulting in presbyopia. With recent studies suggesting that presbyopia may be the result of posterior chamber crowding rather than lens sclerosis alone, there is a growing interest in the surgical correction of presbyopia. Any method that can increase the distance between the ciliary body and the lens equator could therefore enhance the amplitude of accommodation and reverse presbyopia. Anterior ciliary sclerotomy with tissue barriers may be the answer.
It is important to understand the differences in scleral implant technology. Ophthalmologists are aware of scleral expansion bands, the circumferential segments implanted in tunnels in the sclera. The new and different technology discussed here are tissue barriers that are inserted into the ACS radial incisions over the ciliary body. Expansion of the globe circumference is produced by the radial incisions; the tissue barriers maintain that expansion.
ACS is based on the theory of accommodation proposed by Mueller in 1855 and reported by Donders in 1864. Mueller held that accommodation resulted from ciliary body contraction with forward movement of the lens because of forward force of the vitreous.
Mueller’s theory was virtually disregarded by his contemporaries in favor of the theory of Helmholtz, which proposed that ciliary contraction caused relaxing of zonules with resulting alteration of lens curvature. Recent re-evaluation of the evidence has confirmed the anterior movement of the lens-zonule complex as a component of accommodation. When anterior lens movement is coupled with increased convexity of the lens, the power of the lens increases and the eye focuses at near.
It appears that expanding the globe over the ciliary body could be the answer to the “crowded” condition of the aging ciliary-zonular complex, and anything that improves ciliary body-zonular integrity could improve accommodative amplitudes and reverse presbyopia. Recent studies by Johnson, Coleman, Thornton and others have confirmed this conclusion.
The principle of increasing globe circumference with nonpenetrating surface incisions has been demonstrated clinically in radial and astigmatic keratotomy for a number of years. More than 200 cases of ACS with Hays-Fukasaku tissue barriers have been followed for 2 years or more with good retention of restored accommodation.
The procedure
ACS is a straightforward procedure. Preoperatively, patients undergo refraction, keratometry, tonometry and ultrasonic biomicroscopy to measure scleral thickness. Following topical anesthesia and peritomy, a special Duckworth & Kent diamond knife is used to create a 3-mm, 95% thickness radial sclerotomy in each of the oblique quadrants. The sclerotomy is opened to the subscleral space using special spreading forceps, with the bluish blush of the ciliary body serving as the indicator of proper depth for maximal effect. Tissue barriers of titanium or silicone (measuring about 0.6 mm by 0.6 mm by 2.5 mm) are then sutured into the sclerotomy using 10-0 nylon suture. The barriers must be securely fixed in the depth of the incision to ensure maximal effect, limit regression from tissue contraction and avoid barrier extrusion.
Surgical Specialties Corp. is planning to begin formal multicenter clinical studies of these barrier devices in the United States and Europe.
For Your Information:
- Spencer P. Thornton, MD, FACS, can be reached at thornton@eyecareusa.org. Dr. Thornton has a financial interest in this technology.
References:
- Donders FC. Accommodation and Refraction of the Eye. London: New Sydenham Society; 1864:26-27.
- Coleman DJ. Unified model for accommodative mechanism. Am J Ophthalmol. 1970;69(6):1063-1079.
- Coleman DJ. On the hydraulic suspension theory of accommodation. Trans Am Soc Ophthalmol. 1986;84:846-868.
- Thornton SP. Lens implantation with restored accommodation. Current Canadian Ophthalmic Practice. 1986;4(2).
- Thornton SP. Accommodation in pseudophakia. In: SPB Percival, ed. A Colour Atlas of Lens Implantation. St. Louis, Mo.: Mosby Year Book Inc.; 1991.
- Cumming JS, Kammann J. Experience with an accommodating IOL. J Cataract Refract Surg. 1996;22(8):1001.
- Nawa Y, Ueda T, et al. Accommodation obtained per 1.0 mm forward movement of a posterior chamber intraocular lens. J Cataract Refract Surg. 2003;29(11):2069-2072.
- Thornton SP. Astigmatic keratotomy: A review of basic concepts. J Cataract Refract Surg. 1990;16(4):27-31.
- Fukasaku H. Presbyopia correction possible. Ocular Surgery News, Europe/Asia-Pacific Edition. January 1, 2001:42-43.