Use of the light-adjustable lens to correct astigmatism after cataract surgery

Potential role of the light-adjustable lens in flanged intrascleral haptic fixation

PURPOSE

To compare maximum tensile strength between commonly used 3-piece intraocular lens (IOL) for flanged intrascleral haptic fixation (FISHF).

SETTING

Willis-Knight Eye Institute, Shreveport, Louisiana.

DESIGN

Laboratory investigation.

METHODS

Haptic tensile strength was compared with MA60AC, CT Lucia 602, AR40E, and the light-adjustable lens (LAL). Haptic strength with a 24-diopter (D) IOL was compared across all lenses, as well as across a range of 10 to 30 D with the MA60AC. A custom device was created to hold the IOL in correct haptic orientation. The maximum tension (mean ± SD) was recorded in Newtons (N) when the haptic lost tension or broke.

RESULTS

CT Lucia was the strongest at 1.53 ± 0.11 N vs 1.00 ± 0.15 (MA60AC), 0.87 ± 0.19 (AR40E), and 0.83 ± 0.14 N (LAL) ( P < .001). The LAL and AR40E were similar to a 9-0 polypropylene suture while being significantly stronger than 10-0 polypropylene suture ( P < .001). No difference in haptic tension for the MA60AC from 10 to 30 D ( P > .05). High magnification revealed the highest haptic fractures for MA60AC at 40% compared with LAL, AR40E, and CT Lucia at 0%. CT Lucia and AR40E had 100% of haptics disinserted from the IOL without any damage compared with 60% LAL and 60% MA60AC. CT Lucia, AR40E, and LAL have a flatter haptic angulation at 5 degrees.

CONCLUSIONS

Haptic strength, durability, and angulation of the LAL may support the possibility of FISHF in the hands of experienced surgeons. However, further testing is strongly recommended to verify whether physiologic conditions or light treatments may compromise long-term haptic stability.

Toric intraocular lenses: Expanding indications and preoperative and surgical considerations to improve outcomes

Since the introduction of the first toric intraocular lens (IOLs) in the early 1990s, these lenses have become the preferred choice for surgeons across the globe to correct corneal astigmatism during cataract surgery. These lenses allow patients to enjoy distortion-free distance vision with excellent outcomes. They also have their own set of challenges. Inappropriate keratometry measurement, underestimating the posterior corneal astigmatism, intraoperative IOL misalignment, postoperative rotation of these lenses, and IOL decentration after YAG-laser capsulotomy may result in residual cylindrical errors and poor uncorrected visual acuity resulting in patient dissatisfaction. This review provides a broad overview of a few important considerations, which include appropriate patient selection, precise biometry, understanding the design and science behind these lenses, knowledge of intraoperative surgical technique with emphasis on how to achieve proper alignment manually and with image-recognition devices, and successful management of postoperative complications.

Astigmatic correction with implantation of a light adjustable vs monofocal lens: a single site analysis of a randomized controlled trial

AIM

To evaluate the light adjustable lens (LAL) vs a standard monofocal lens in achieving target astigmatic refraction and improving postoperative uncorrected distance visual acuity (UDVA).

METHODS

This randomized controlled clinical trial included 40 patients with pre-existing astigmatism and visually significant cataract. Twenty-eight patients received the LAL and 12 control patients received a monofocal intraocular lens (IOL) after cataract extraction at a single institution. The patients with the LAL underwent adjustment by ultraviolet (UV) light postoperatively plus subsequent lock-in procedures and all patients returned to clinic for follow up of study parameters at 6, 9, and 12mo. Manifest refraction, distance visual acuity, and adverse events were recorded at each visit.

RESULTS

The mean cylinder before adjustment in eyes with the LAL was -0.89±0.58 D (-2.00 to 0.00 D) and -0.34±0.34 D (-1.25 to 0.00 D) after lock-in (P=1.68x10^-8). The mean cylinder in patients with the monofocal lens was -1.00±0.32 D (-1.50 to -0.50 D) at 17-21d postoperatively, which was statistically different from the LAL cylinder post lock-in (P=1.43x10^-6). UDVA in the LAL group was 20/20 or better in 79% of patients post lock-in with good stability over 12mo compared with 33% of the control patients with UDVA of 20/20 or better.

CONCLUSION

These results demonstrate that the LAL is more effective in achieving target refractions and improving postoperative UDVA in patients with pre-existing corneal astigmatism than a standard monofocal lens.

Optimizing outcomes with toric intraocular lenses

Toric intraocular lenses (IOLs) are the procedure of choice to correct corneal astigmatism of 1 D or more in cases undergoing cataract surgery. Comprehensive literature search was performed in MEDLINE using “toric intraocular lenses,” “astigmatism,” and “cataract surgery” as keywords. The outcomes after toric IOL implantation are influenced by numerous factors, right from the preoperative case selection and investigations to accurate intraoperative alignment and postoperative care. Enhanced accuracy of keratometry estimation may be achieved by taking multiple measurements and employing at least two separate devices based on different principles. The importance of posterior corneal curvature is increasingly being recognized in various studies, and newer investigative modalities that account for both the anterior and posterior corneal power are becoming the standard of care. An ideal IOL power calculation formula should take into account the surgically induced astigmatism, the posterior corneal curvature as well as the effective lens position. Conventional manual marking has given way to image-guided systems and intraoperative aberrometry, which provide a mark-less IOL alignment and also aid in planning the incisions, capsulorhexis size, and optimal IOL centration. Postoperative toric IOL misalignment is the major factor responsible for suboptimal visual outcomes after toric IOL implantation. Realignment of the toric IOL is needed in 0.65%–3.3% cases, with more than 10° of rotation from the target axis. Newer toric IOLs have enhanced rotational stability and provide precise visual outcomes with minimal higher order aberrations.

Refractive accuracy with light-adjustable intraocular lenses

PURPOSE

To evaluate efficacy, predictability, and stability of refractive treatments using light-adjustable intraocular lenses (IOLs).

SETTING

University Hospital Virgen de la Arrixaca, Murcia, Spain.

DESIGN

Prospective nonrandomized clinical trial.

METHODS

Eyes with a light-adjustable IOL (LAL) were treated with spatial intensity profiles to correct refractive errors. The effective changes in refraction in the light-adjustable IOL after every treatment were estimated by subtracting those in the whole eye and the cornea, which were measured with a Hartmann-Shack sensor and a corneal topographer, respectively. The refractive changes in the whole eye and light-adjustable IOL, manifest refraction, and visual acuity were obtained after every light treatment and at the 3-, 6-, and 12-month follow-ups.

RESULTS

The study enrolled 53 eyes (49 patients). Each tested light spatial pattern (5 spherical; 3 astigmatic) produced a different refractive change (P<.01). The combination of 2 light adjustments induced a maximum change in spherical power of the light-adjustable IOL of between -1.98 diopters (D) and +2.30 D and in astigmatism of up to -2.68 D with axis errors below 9 degrees. Intersubject variability (standard deviation) ranged between 0.10 D and 0.40 D. The 2 required lock-in procedures induced a small myopic shift (range +0.01 to +0.57 D) that depended on previous adjustments.

CONCLUSIONS

Light-adjustable IOL implantation achieved accurate refractive outcomes (around emmetropia) with good uncorrected distance visual acuity, which remained stable over time. Further refinements in nomograms and in the treatment's protocol would improve the predictability of refractive and visual outcomes with these IOLs.

FINANCIAL DISCLOSURE

No author has a financial or proprietary interest in any material or method mentioned.

Adjustable intraocular lens power technology

We present an overview of the adjustable intraocular lens (IOL) technologies that are available or under development. This includes IOL technologies that can be adjusted using secondary surgical procedures, such as the multicomponent IOL, the mechanically adjustable IOL, and the repeatedly adjustable IOL; IOLs that can be adjusted noninvasively in the postoperative setting, such as the magnetically adjustable IOL, the liquid crystal IOLs with wireless control; and IOLs that can be adjusted using the femtosecond laser or 2-photon chemistry. Finally, we discuss the preclinical and clinical studies of the light-adjustable intraocular lens (LAL) that is available commercially in Europe and Mexico and in the final stages of clinical evaluation in the United States. The general principles of each technology, as well as their research status, are described.

FINANCIAL DISCLOSURE

No author has a financial or proprietary interest in any material or method mentioned.

Corrective Techniques and Future Directions for Treatment of Residual Refractive Error Following Cataract Surgery

Postoperative residual refractive error following cataract surgery is not an uncommon occurrence for a large proportion of modern-day patients. Residual refractive errors can be broadly classified into 3 main categories: myopic, hyperopic, and astigmatic. The degree to which a residual refractive error adversely affects a patient is dependent on the magnitude of the error, as well as the specific type of intraocular lens the patient possesses. There are a variety of strategies for resolving residual refractive errors that must be individualized for each specific patient scenario. In this review, the authors discuss contemporary methods for rectification of residual refractive error, along with their respective indications/contraindications, and efficacies.

The visual and functional impacts of astigmatism and its clinical management

PURPOSE

To provide a comprehensive overview of research examining the impact of astigmatism on clinical and functional measures of vision, the short and longer term adaptations to astigmatism that occur in the visual system, and the currently available clinical options for the management of patients with astigmatism.

RECENT FINDINGS

The presence of astigmatism can lead to substantial reductions in visual performance in a variety of clinical vision measures and functional visual tasks. Recent evidence demonstrates that astigmatic blur results in short-term adaptations in the visual system that appear to reduce the perceived impact of astigmatism on vision. In the longer term, uncorrected astigmatism in childhood can also significantly impact on visual development, resulting in amblyopia. Astigmatism is also associated with the development of spherical refractive errors. Although the clinical correction of small magnitudes of astigmatism is relatively straightforward, the precise, reliable correction of astigmatism (particularly high astigmatism) can be challenging. A wide variety of refractive corrections are now available for the patient with astigmatism, including spectacle, contact lens and surgical options.

CONCLUSION

Astigmatism is one of the most common refractive errors managed in clinical ophthalmic practice. The significant visual and functional impacts of astigmatism emphasise the importance of its reliable clinical management. With continued improvements in ocular measurement techniques and developments in a range of different refractive correction technologies, the future promises the potential for more precise and comprehensive correction options for astigmatic patients.

Extended depth of focus with induced spherical aberration in light-adjustable intraocular lenses

PURPOSE

To evaluate the quality of vision and depth of focus induced by controlled amounts of negative spherical aberration in patients implanted bilaterally with light-adjustable intraocular lenses.

DESIGN

Prospective, nonrandomized clinical trial.

METHODS

Seventeen patients were implanted and treated with appropriate spatial irradiance light profiles. One eye was set for emmetropia, and the fellow eye received an additional aspheric light treatment to induce controlled amounts of negative spherical aberration. We used a Hartmann-Shack sensor to measure the eye's refraction and aberrations for a 4-mm pupil diameter. Decimal visual acuity (VA) was measured using a micro-display placed at 10 m, 60 cm, 40 cm, and 30 cm.

RESULTS

Eyes treated with aspheric profiles were divided into 2 groups depending on the final amount of induced negative spherical aberration: low [-0.05, -0.10 μm] and high [-0.13, -0.23 μm]. In both groups, the mean uncorrected decimal VA at 60 cm was over 0.90. In the first group, distance VA was 0.97 ± 0.16, but in the second group it was lower (0.76 ± 0.16). As expected, the VA for nearer distances is higher in the eyes with a larger magnitude of spherical aberration (P value < .01): 0.94 ± 0.10 and 0.73 ± 0.16 at 40 and 30 cm, respectively, in comparison with 0.71 ± 0.15 and 0.50 ± 0.14. Binocular summation with the fellow eye, adjusted for emmetropia, produces an excellent binocular distance VA (>1.10) in both groups.

CONCLUSIONS

Controlled amounts of negative spherical aberration and defocus can be induced in eyes implanted with adjustable intraocular lenses to enhance near vision.

Toric intraocular lenses: historical overview, patient selection, IOL calculation, surgical techniques, clinical outcomes, and complications

We present an overview of currently available toric intraocular lenses (IOLs) and multifocal toric IOLs. Relevant patient selection criteria, IOL calculation issues, and surgical techniques for IOL implantation are discussed. Clinical outcomes including uncorrected visual acuity, residual refractive astigmatism, and spectacle independency, which have been reported for both toric IOLs and multifocal toric IOLs, are reviewed. The incidence of misalignment, the most important complication of toric IOLs, is determined. Finally, future developments in the field of toric IOLs are discussed.

Design and validity of a miniaturized open-field aberrometer

PURPOSE

To design and validate a new miniaturized open-field wavefront device that can be attached to an ophthalmic surgical microscope or slitlamp.

SETTING

Solihull Hospital and Aston University, Birmingham, United Kingdom.

DESIGN

Comparative noninterventional study.

METHODS

The dynamic range of the Aston aberrometer was assessed using a calibrated model eye. The validity was compared with that of a conventional desk-mounted Hartmann-Shack aberrometer (Topcon KR1W) in dilated eyes. The instruments were used in random order, with measurements repeated 5 times to assess intrasession repeatability.

RESULTS

The open-field aberrometer had a large dynamic range of at least +21.0 diopters (D) to -25.0 D. It gave similar measurements to the conventional aberrometer for mean spherical equivalent (SE) (mean difference 0.02 D ± 0.49 [95% confidence interval]; correlation r = 0.995; P<.001), astigmatic components (J0: 0.02 ± 0.15 D; r = 0.977, P<.001; J45: 0.03 ± 0.28, r = 0.666, P<.001), and higher-order aberration (HOA) root mean square (RMS) (0.02 ± 0.20 D, r = 0.620, P<.001). Intraclass correlation coefficient assessments of intrasession repeatability were excellent (SE = 1.000, P<.001; J0 = 0.998, P<.001; J45 = 0.980, P<.01; HOA RMS = 0.961, P<.001).

CONCLUSIONS

The new aberrometer gave valid, repeatable measurements of refractive error and HOAs over a large range. It can measure continuously, thus providing direct feedback on the optical status of the visual system to surgeons during intraocular lens implantation and corneal surgery.

Prevalence of corneal astigmatism in patients having routine cataract surgery at a teaching hospital in the United Kingdom

PURPOSE

To analyze and quantify the pattern of corneal astigmatism in patients awaiting cataract surgery and to establish the demand for toric intraocular lenses (IOLs) in a hospital unit.

SETTING

Singleton Hospital Abertawe Bro Morgannwg University NHS Trust, Swansea, United Kingdom.

DESIGN

Cross-sectional study.

METHODS

Keratometric measurements of all patients attending the preassessment clinic over a 4-month period were prospectively collected and analyzed.

RESULTS

The study comprised 1230 eyes of 746 patients with a mean age of 75.54 years ± 0.71 (SD). The corneal astigmatism was 0.50 diopter (D) or less in 301 eyes (24.47%), 1.50 D or less in 978 eyes (79.50%), more than 2.50 D in 57 eyes (4.61%), and 3.00 D or more in 24 eyes (1.93%).

CONCLUSIONS

Of patients attending for routine cataract surgery at a single center, 497 (40.41%) had more than 1.00 D of astigmatism. The results can help hospitals analyze the demand for and cost of using toric IOLs in patients with corneal astigmatism.

FINANCIAL DISCLOSURE

Neither author has a financial or proprietary interest in any material or method mentioned.