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Abstract
Aim To determine if residual cylindrical refractive error after cataract surgery can be adjusted using the light-adjustable lens (LAL).
Methods The LAL is a photosensitive silicone intraocular lens whose power can be adjusted post-operatively using UV light at 365 nm. A digital light delivery device (DLD) is used to adjust LAL power in situ to correct residual refractive errors non-invasively. Profiles developed to correct residual cylindrical and spherical errors were tested on five patients, with postoperative toric refractive errors of 1.25–1.75 D. At 2 weeks post-implantation, best corrected visual acuity (BCVA), uncorrected visual acuity (UCVA) and residual refractive errors were measured.
Results Toric error was reduced in each of the patients and refractions remained stable for the 9 month follow-up period. Achieved spherical equivalent manifest refraction (MRSE) was within 0.25 D of targeted emmetropia. All five patients improved their UCVA to ≥20/25 (≤0.1 logarithm of the minimum angle of resolution (LogMAR)) and maintained their BCVA.
Conclusion The LAL can be adjusted postoperatively to correct residual astigmatism.
- Light adjustable lens
- astigmatism
- intraocular lens
- cataract
- refractive error
- vision
- optics and refraction
- treatment surgery
- treatment other
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- Light adjustable lens
- astigmatism
- intraocular lens
- cataract
- refractive error
- vision
- optics and refraction
- treatment surgery
- treatment other
Introduction
While use of partial coherence interferometry (IOL Master; Carl Zeiss-Meditec, Jena, Germany) has improved prediction of intraocular lens (IOL) power, residual astigmatism after cataract surgery remains a significant cause of reduced uncorrected visual acuity (UCVA). In a series of 7500 eyes undergoing cataract surgery, Hoffer showed that 1770 (23.6%) had≥1.5 D of corneal astigmatism.1 Residual astigmatism of as little as 0.75 D can reduce UCVA and cause haloes.2 Surgical methods to treat astigmatism include corneal and limbal relaxing incisions, toric IOLs (eg, Staar Toric IOL (Staar Surgical, Monrovia, California, USA) and AcrySof toric IOL (Alcon Laboratories, Fort Worth, Texas, USA)), and postoperative laser-assisted keratomileusis (LASIK) or photoreactive keratotomy (PRK) (bioptics). Relaxing incisions can correct low and moderate astigmatic errors, but can be complicated by placement on the incorrect axis, perforation, pain and infection.2–4 Toric IOLs are also subject to misalignment, postoperative rotation and limited number of powers.5–7 Finally, excimer laser surgery performed in the postoperative period requires a second procedure, often by a different surgeon, since many cataract surgeons do not perform refractive surgery.
An alternative approach to treating astigmatism postoperatively is the light-adjustable intraocular lens (LAL) (figure 1).8–11 The LAL contains photosensitive silicone macromers homogeneously dispersed within a silicone matrix that allows the refractive power of the lens to be adjusted postoperatively by the application of spatially profiled near-ultraviolet (UV) light (365 nm). Clinically, the refractive properties of the LAL are adjusted using the digital light delivery (DLD) device (figure 1). The DLD generates the required spatial irradiance pattern using a digital mirror device (DMD; Texas Instruments, Dallas, Texas, USA) and projects it onto the implanted LAL. The versatility of the DMD chip enables customisation of the irradiation profile to correct both sphere and astigmatism, as well as higher order aberrations.
(A) The light-adjustable lens (LAL). It has a 6 mm bi-convex optic with modified C-polymethyl methacrylate (C-PMMA) haptics, a square posterior edge, rounded anterior edge, and a posterior UV blocking layer of≤100 μm thick. (B) The digital light delivery (DLD) device. It projects 365 nm UV light onto the LAL for both adjustment and lock-in. The spatial irradiance pattern for adjustment is generated using a digital mirror device that contains an array of approximately 785 000 mirrors.
For correction of astigmatism an irradiation pattern is generated and aligned with the astigmatic axis. We have previously reported on correction of astigmatism in vitro.9 The objective of this study was to test whether we could correct residual cylindrical refractive error postoperatively in patients undergoing cataract surgery with implantation of the LAL.
Materials and methods
Subjects with visually significant cataract who had 0.75–2.0 D of corneal astigmatism and excellent visual potential were screened for eligibility. Subjects with more than 2 D of preoperative astigmatism, anterior segment pathology, uncontrolled glaucoma, previous ocular surgery, current use of Flomax (Boehringer Ingelheim Pharmaceuticals, Inc., Ridgefield, Connecticut, USA), or <7.0 mm dilated pupils were excluded. Preoperative biometry was performed using an immersion biometry unit (Axis II Ophthalmic Echograph; Quantel Medical, Bozeman, Montana, USA).
Five patients who met the inclusion and exclusion criteria were enrolled for this pilot study. Patients underwent phacoemulsification using topical anaesthetic and clear corneal incision (3.5 mm). The LAL was implanted in the capsular bag using Nichamin II foldable lens insertion forceps. The operative eye was patched following surgery. The patch was removed the following day, and patients were instructed to wear UV-blocking photochromic spectacles at all times until the adjustment and lock-in procedures were completed.
At 2 weeks post-implantation, visual acuity (BCVA and UCVA) and residual refractive error were measured by manifest refraction. The DLD was used to adjust LAL power to correct both the spherical and astigmatic error, attempting to achieve emmetropia. Further irradiation treatment was given a minimum of 20 hours after adjustment to lock-in the lens. The five patients had 9 months follow-up each. The following study endpoints were evaluated:
Visual acuity (BCVA and UCVA) expressed in logarithm of the minimum angle of resolution (LogMAR) scale
Attempted versus achieved lens power change (manifest refraction)
Stability of adjusted lens power at 1 week, and 4–6 and 9 months (manifest refraction)
Results
The five patients with astigmatism and implanted with LALs are listed in table 1. They ranged in age from 60 to 87 years old (mean 68 years). Each was followed up for 9 months. Toric error was reduced in each of the five patients and refractions remained stable after lock-in for the 9 month follow-up period. Following adjustment and lock-in, 0.5 D of cylinder remained in all five patients, resulting in a ≤0.1 LogMAR difference between UCVA and BCVA. All patients improved their UCVA and had final UVCA ≤0.1 LogMAR. No patient lost BCVA. While all five patients wore spectacles for distance correction preoperatively, distance spectacles have not been prescribed post-adjustment.
Treatment data of five patients with astigmatism
Discussion
Use of the LAL to correct astigmatism offers advantages over current means of refractive correction. Because final refractive outcome is not always predictable, the LAL is not adjusted until the postoperative period when spectacles would ordinarily be prescribed. This would seem preferable to limbal relaxing incisions, which are not only less precise, but also are made intraoperatively. Toric IOLs seem to offer many of the same advantages as the LAL, but their powers are limited, they must be precisely aligned at surgery and they may be subject to some postoperative rotation that diminishes toric correction. In addition, preoperative biometry errors leading to unintended spherical errors will compound any uncorrected astigmatism. Finally, correcting cylinder with the LAL is preferable to LASIK because it is non-invasive and avoids complications such as dry eye that might be more common in older patients undergoing cataract surgery.12 The LAL power can be readjusted until it is locked-in. Maximal spherical or cylindrical adjustments achieved with one adjustment are approximately 2.0 D. Subsequent adjustment prior to lock in can add an additional 0.5 D (C Sandstedt, unpublished data). Leaving the LAL unlocked would subject the lens to untoward optical changes from ambient UV light.
In summary, we have demonstrated feasibility of using the LAL to correct residual toric errors following cataract surgery. Correction of up to 1.25 D of residual astigmatism was performed in five patients using the DLD; UCVA improved in all five patients and none lost BCVA. While all five patients no longer required spectacle correction for distance acuity, reading glasses remained a necessity at near.
This method of postoperative, non-invasive correction would seem preferable to invasive alternatives such as LASIK and limbal relaxing incisions.12 13
Footnotes
Funding Funding for this study was provided by Calhoun Vision, Inc.
Competing interests CS, SC and BT are employees and stockholders of Calhoun Vision, Inc. RG and DS are stockholders of Calhoun Vision.
Patient consent Obtained.
Ethics approval Ethics approval was provided by Mexican Ministry of Health and the Institutional Review Board at Codet Vision Institute (Tijuana, Mexico).
Provenance and peer review Not commissioned; externally peer reviewed.
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