NEW-ERA IOLS

Refractive surprise; glare and haloes; lens tilt, dislocation and decentration; residual astigmatism; aberrations and loss of contrast sensitivity – successful as cataract surgery is in restoring vision, these remain vexing challenges. They particularly affect presbyopia treatment, but also standard monofocal IOL implantation.

New and developing lens designs combined with new lenticular surgery technology hold promise for finally overcoming these problems. The result could be clearer vision for all IOL patients as well as presbyopia treatment without optical compromise, proponents say.

The precision offered by femtosecond laser-assisted cataract surgery has inspired new designs that address many of these issues, said Julian Stevens MRCP, FRCS, FRCOphth, DO, consultant surgeon at Moorfields Eye Hospital, London, UK. Perfectly sized, shaped and positioned capsulotomies enable capsulotomy-fixated lenses, with a groove in the optic that captures the capsulotomy edge much as a tyre fits into a bicycle rim, he explained.

Marie-Jose Tassignon MD, PhD has long been a proponent of both the anterior and a posterior capsulorrhexis being captured at the edge of the lens implant optic, rather than rely on haptic fixation. Nishi first proposed capturing the lens optic by the capsulorrhexis, but it is only now with precise femtosecond laser capsulotomy that a reliable size, shape and position can be achieved, according to Dr Stevens.

Bag-in-the-lens – Tassignon
Courtesy of Jack Holladay MD

As long as the capsular bag remains stable, capsulotomy-fixated lenses should remain perfectly centred and settle at a predictable depth effectively eliminating aberrations resulting from lens tilt, decentration or incorrect distance from the retina, said Dr Stevens, who is working with Oculentis GmbH in the Netherlands developing a hydrophobic surface acrylic lens with capsulotomy fixation and which has CE marking. The wedge shape of the groove edge overlapping the anterior capsule surface also aims to eliminate internal reflections off the square edge of in-the-bag designs. The capsulotomyfixated lens also sits further forwards than a bag-fixated lens, requiring a lower A constant in power calculations.

A similar design developed by Samuel Masket MD, of the David Geffen School of Medicine, Jules Stein Eye Institute at the University of California Los Angeles, US, is manufactured by Morcher GmbH, Stuttgart, Germany. It was specifically designed to eliminate negative dysphotopsias, which Dr Masket found were caused by in-the-bag designs regardless of lens material.

H Burkhard Dick MD, PhD, Bochum, Germany, is researching the Morcher anti-dysphotopsia lens, which was also CE marked last year. Five lenses implanted in five patients showed no negative or positive dysphotopsias or evidence of iris chafe, Jack Holladay MD, of Baylor College of Medicine, Houston, US, told Cornea 2013 at the annual meeting of the American Academy of Ophthalmology in New Orleans. The bag-in-lens designed by Prof Tassignon, University Hospital Antwerp, Belgium, also provides this benefit, Dr Holladay added. “Both anterior and posterior capsulotomy fit in a flange on the lens, eliminating PCO as well as any reflection from a rounded or square edge.”

Dr Stevens noted that femtosecond laser technology may make it easier to create the precise capsulotomies required for the bag-in-lens. He also pointed out that it allows centring the capsulotomy to the desired coronal point; on the optical axis, visual axis or the dilated or undilated pupil, which is his preference. “The lens allows precise x-y coronal placement. This could make possible wavefront correction and topography optimisation similar to that offered by laser refractive surgery. For the first time we can have customised lenses.”

However, the long-term stability of capsulotomy-fixated lenses remains to be demonstrated, and some early expectations for the precision of femtocataract surgery with conventional IOLs have not panned out. “This may be because they are geometrically centred within the capsular bag, rather than over the laser capsulotomy, so there is a possible relative decentration,” Dr Stevens said.

Several studies have found little or no significant difference in accuracy of effective lens position or visual outcomes between femto-cataract and ultrasound phaco patients.

FluidVision Lens
(Courtesy of Louis D Nichamin MD)

IN-SITU LENS ADJUSTMENT

Precisely positioning lenses becomes less critical if the characteristics of those lenses can be adjusted after they are implanted. Adjustable lenses may correct not only sphere and cylinder power, but also aberrations, said Dr Holladay, who highlighted three approaches. Available in Europe since 2008 and currently in US clinical trials, the Light Adjustable Lens, or LAL (Calhoun Vision) is an aspheric three-piece IOL with a 6.0mm optic constructed of ultraviolet-sensitive silicone polymers. This allows sphere and cylinder adjustment of about 2.0 D as well as correction of aberrations using a special lamp. Once good vision is achieved, the correction is locked in using a different light source. It has successfully corrected spherical aberrations and coma, Dr Holladay noted.

The LAL is an especially good choice for eyes that have undergone LASIK or corneal crosslinking, or with cataracts making it impossible to get a precise intraocular lens power calculation, according to Tobias H Neuhann MD, Munich, Germany. He has implanted LALs in more than 100 eyes and reported results at several ESCRS meetings.

In a series of 65 eyes with an astigmatism not larger than 2.0 D, all achieved 20/30 or better uncorrected at 24 months – including 24 complicated eyes of which 13 were post-LASIK, two with keratoconus and nine with no IOL Master axial length reading. The LAL eyes also achieved good near vision, with two-thirds achieving J6 or better, compared with about two per cent of conventional monofocal eyes. Dr Neuhann believes the effect results from induction of coma in the LAL. The astigmatism of up to 2.0 D was reduced to a mean of about 0.5 D cylinder, Dr Neuhann reported. He considers the LAL the best option available for treating astigmatism of up to 2.0 D to 3.0 D cylinder because it corrects precisely based on the patient’s actual post-op refraction rather than a pre-op estimate.

The LAL can also be used to apply monovision, Dr Neuhann said. The patient lives with the refraction for two weeks before locking in, ensuring that it can be tolerated. The biggest drawbacks of the LAL are cost – about €1,000 additional per lens – the need for two or three weeks' follow-up visits to adjust and set lens power, and the need for patients to wear UV-blocking sunglasses during the adjustment period to avoid power changes due to natural UV light, Dr Neuhann said. Nevertheless this investment lasts for a lifetime.

A femtosecond laser capable of adjusting conventional IOLs in situ is also under development by Aaren Scientific of Ontario, California, US, Dr Holladay said. Laser energy selectively changes the refractive index of a layer of material approximately 50 microns thick within the IOL, creating a layer of higher refractive index material that can be shaped to adjust lens power, toricity and asphericity.

Dual optics is a third approach, Dr Holladay said. The Harmoni lens under development by ClarVista Medical, Aliso Viejo, California, US, is a modular system incorporating a base with haptics implanted in the capsular bag with a removable optic. Lens power can be changed by replacing the optic without explanting the haptics. Restoring vision across the entire distance spectrum is the Holy Grail of IOL design, Dr Holladay observed. But multifocal lenses, the most common current choice, also generate haloes, glare and loss of contrast sensitivity unacceptable to many patients. Several approaches are in the works that address these challenges.

Courtesy of Jack Holladay MD

The extended depth of focus lens is an optical solution, Dr Holladay said. These combine a diffractive optical element with a refractive lens, creating a smooth focus over a greater depth field than a conventional monofocal lens, but without loss of contrast sensitivity or distance acuity. “We see several of these coming down the pipeline from several companies.” The Lumina lens from AkkolensTM, Breda, The Netherlands, provides mechanical accommodation with a dual optic lens that change power by moving laterally under contraction of the ciliary muscles. Inserted through a 2.8mm incision, the lens has been implanted in about 50 healthy eyes, and provides 4.0 D to 7.0 D of accommodation, according to company reports.

The FluidVisionTM lens from PowerVision, Belmont, California, US, consists of a central optic surrounded by fluid-filled haptics made up of a proprietary acrylic material containing ophthalmic-grade silicon. With contraction and relaxation of the ciliary muscles, fluid is pushed between the haptics and the flexible optic, changing its shape and refractive power. In trials of a non-foldable version reported by Louis D “Skip” Nichamin MD, Brookville, Pennsylvania, US, 14 patients achieved best corrected distance visual acuity ranging from 20/18 to 20/29, while subjective accommodation using push-down test exceeded, on average, 5.0 D. A foldable version that can be inserted through a sub-4.0mm incision has also been implanted now in 39 patients. The first 20 patients have been reported upon, with results showing that patients achieved an average of 4 D of accommodation with distance acuity averaging 20/19.

The NuLens uses a similar concept, but fluid in a cylinder pushes the anterior optic back and forth, Dr Holladay said. The FlexOptic is a flexible lens designed using finite analysis to detract power from the periphery and increase it in the centre as the bag contracts. Several companies are also working on injectable polymers, Dr Holladay said. One is the SmartIOL from Medennium, Irvine, California, US, which is injected shaped as a rod, but changes shape when it warms up to body temperature. It fills the capsular bag and is malleable enough to change shape similar to the crystalline lens. LiquiLens from Vision Solutions Technologies, Rockville, Maryland, US, uses gravity to accommodate, Dr Holladay said. When looking down, a high refractive index fluid flows from a reservoir producing a 3.0 D or more add.

Elenza, Roanoke, Virginia, US, is developing an electronic accommodating lens, Dr Holladay said. It consists of two rechargeable batteries, integrated circuits and a central 3.0mm liquid crystal optic zone hermetically sealed inside a hydrophobic acrylic IOL. Lens power is controlled by a complex algorithm that relates pupil contraction and eye conditions with accommodative intent.

The speed and amplitude of pupillary response to accommodation differs from that in response to light changes. “This circuitry is set up so that when the eye looks closer, the lens detects the pupil constriction and increases power. But it also measures light level so it is not fooled by walking outside on a bright day, which also causes pupil constriction,” Dr Holladay explained.

AcuFocus, Irvine, California, US, is developing an IOL implant similar to its corneal inlay. Based on the pinhole concept, the lens increases depth of focus in the non-dominant eye, Dr Holladay said. New lenses that darken to block unwanted wavelengths when exposed to sunlight, similar to photochromic spectacle lenses, will block unwanted rays when needed, but be completely clear in low light. “We have a lot of new lenses in the pipeline and you will begin seeing these in the not-too-distant future,” he concluded. 

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