Laser scleral microporation: Unique method to treat presbyopia goes back to basics
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Key takeaways:
- Laser scleral microporation, or LSM, from Ace Vision Group is a therapeutic solution for presbyopia.
- John Marshall, PhD, FRCPath, FMedSci, and colleagues have analyzed the physiology of accommodation.
Laser scleral microporation is a unique therapeutic solution for presbyopia that goes back to basics, rejuvenating the eye and restoring the natural dynamic mechanism of accommodation and disaccommodation.
“Nature frequently develops dynamic processes, which work well for most individuals for the first 40 or 50 years of life but then, because of changes in the intrinsic properties of some or all the various components involved, begin to break down,” John Marshall, PhD, FRCPath, FMedSci, told Healio.
Various theories have been postulated to explain presbyopia. The most widely accepted is the classic model based on the concept that the crystalline lens hardens and increases in volume with age, thereby becoming less deformable. Other theories have looked at changes in the elasticity of the capsule, the potential progressive atrophy of the ciliary muscles as well as loss of tension or slackening of the zonules.
Current solutions to this loss of dynamic range of focus with age have focused almost exclusively on the use of lenses, predominantly spectacles but more recently a range of IOLs post-cataract surgery. Almost without exception, the solutions are not fully dynamic in their focusing ability. Marshall and colleagues at Ace Vision Group have fully analyzed the physiology of accommodation, highlighting the interaction of structures within the anterior segment and between both the anterior and posterior segments of the eye.
“Accommodation to the near field occurs when the ciliary muscles move inward and forward, thereby slackening tension on the lens and allowing the lens to increase in curvature and effectively become fatter, providing the ability to focus on near objects. When we return to distance vision, the ciliary muscles move outward and backward, and the tension on the zonules is therefore relaxed. However, it is not fully appreciated that this process is further facilitated by something we call target recoil in which elastic components associated with the posterior globe facilitate the process of relaxation or disaccommodation,” Marshall said.
The zonules, he explained, anchor in two places. The first location, small anchoring fibers in the valleys of the pars plicata, allows lens changes associated with ciliary muscle movement. The second location arises after the zonules pass over the pars plana and find insertion adjacent to Bruch’s membrane over the choroid. With accommodation, elastic stress is therefore created in Bruch’s membrane beneath the retina, and the structure moves forward, coming under tension. The tips of the photoreceptors, which are embedded in the pigment epithelium, which in turn is anchored to Bruch’s membrane, therefore move forward and can do so because they can swing on the cilium junction between the inner and outer segments. In the disaccommodation phase, the same target recoil elastic component pulls the whole system back into its relaxed mode.
“The design of the retina is so exquisite that in the fovea, where you don’t want the photoreceptor cells to move axially, there is a tertiary compensation system whereby long interconnecting fibers in the photoreceptor cells (up to 500 µm), which constitute the fiber layer of Henle, maintain orientation and allow the Stiles-Crawford effect to be preserved,” Marshall said.
Reinstating a lost function
The progressive increase in ocular rigidity, which occurs with age due to increased collagen cross-linking, affects the capabilities of both the accommodative and dis accommodative mechanisms of the eye. Scleral rigidity in particular has been found to play a key role in inhibiting ciliary muscle function.
“Scleral cross-linking just behind the limbus acts as a resistance to Bruch’s recoil and resists disaccommodation forces,” Marshall said. “The basic concept behind laser scleral microporation (LSM) is to compensate for the scleral cross-linking by producing micro-evaporation of scleral components in order to reduce resistance, thereby allowing the elastic recoil effect to be reconstituted. In a sense, LSM is rejuvenating the entire natural cycle of the accommodative process.”
LSM uses the VisioLite Er:YAG laser (Ace Vision Group) to create arrays of partial-thickness micropores, removing cross-linked scleral bonds in five critical zones in the sclera. This allows the ciliary muscles to move more freely, reviving the natural process of accommodation and decreasing resistance to Bruch’s membrane recoil to rejuvenate disaccommodation.
“An algorithm calculates in relation to the individual patient the number of pulses required and the depth of change that’s needed in the sclera,” Marshall said.
With the latest technology upgrades, an AI-modulated algorithm guides the selection of specific treatments for specific patients and sets up a robotic laser system to carry out the procedure.
“To date, the procedure has been not fully robotic, but the results have been extremely good in at least two offshore trials, which show quite clearly that the system is effective in reinstating accommodation,” Marshall said.
For more information:
John Marshall, PhD, FRCPath, FMedSci, Frost Professor of Ophthalmology at Institute of Ophthalmology University College, London, and emeritus professor of ophthalmology at King’s College London, can be reached at eye.marshall@googlemail.com.
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