The principle behind a new intraocular implant dates back to Aristotle’s observations on the pinhole effect in the 4th century BCE. Over the years, the pinhole effect has been applied frequently in ophthalmology. For example, patients with irregular corneal astigmatism as a result of RK, PKP, keratoconus, pellucid marginal degeneration, corneal trauma, or corneal irregularities usually achieve better visual acuity with a pinhole than with their best-possible refraction. This is mainly because of the presence of an array of corneal aberrations. Use of a small aperture reduces the size of the circle of confusion on the retina, minimizing the impact of corneal aberrations on the optical system.
The same small-aperture principle can also be applied for the correction of pseudophakic presbyopia by extending the depth of focus, especially when coupled with mini-monovision (-0.75 D difference between eyes) in bilateral monofocal pseudophakia. Because of the flattening effect of the small aperture on the defocus curve, the result is good UCVA at near, intermediate, and distance. Additionally, this strategy supplies better distance UCVA in the near-dominant eye than with conventional monovision and fewer compromises in stereopsis.
The XtraFocus, in development by Morcher, is a one-piece, small-aperture diaphragm designed for implantation in the ciliary sulcus in pseudophakic eyes, similar to a piggyback IOL (Figure 1; eyetube.net/?v=emeed). Made of a black foldable hydrophobic acrylic material, the implant has a small central opening (1.3 mm in the current version) with no refractive power and three closed-loop haptics to ensure good centration. The material is opaque to visible light (Figure 1A) but 100% transparent to infrared light (Figure 2), allowing examination of the retina with devices that operate in this portion of the light spectrum, such as OCT and scanning laser ophthalmoscopy.
Figure 1. The small aperture intraocular diaphragm (A) is intended for sulcus implantation in pseudophakic eyes (B).
Figure 2. The implant is 100% transparent to infrared light.
Figure 3. The device in an eye with irregular astigmatism due to a corneal transplant.
To treat presbyopia in pseudophakic patients with normal corneas, we have recently begun implanting the device in only the nondominant eye (Figure 3). To date, we have performed the procedure in 16 eyes, with a mean follow-up of 11 months. All patients with irregular astigmatism had significantly improved visual acuity and reduced dysphotopic symptoms. We are now working with the manufacturer on minor design adjustments.
In my opinion, the greatest feature of this technology is that it is based on simple and reliable principles such as the pinhole effect and secondary IOL implantation. Early adopters can remain in their surgical comfort zone with a minimal learning curve. Other benefits are that results can be simulated preoperatively with pinhole occlusion, and the treatment is easily reversible.
Claudio C. Trindade, MD
- Board of Directors, Cancado-Trindade Eye Institute, Belo Horizonte, Brazil
- Faculty Member, IOCM Faculdade de Ciencias Medicas, Belo Horizonte, Brazil
- Financial disclosure: Patent or part ownership, Royalty agreement (Morcher)