Intraocular Lenses

Delicate Acrylics for New Eyesight

April 29, 2010

Only a few decades ago, the diagnosis "cataracts" meant loss of vision in the near future. Today, cataract surgery is the most common operation worldwide. Thanks to new types of artificial lenses like the ones developed and produced by the HumanOptics AG in Erlangen, Germany, physical discomfort is reduced to a minimum. In the quality control department of HumanOptics, a high-end stereomicroscope ensures the best possible product quality and therefore optimal safety for the patient.

When vision gradually becomes like looking through a pane of frosted glass, it is usually due to opacification of the eye lens, a disorder known as cataracts. Cataracts are mainly age-related and are most common in people in their fifties.

Fig. 1: Diffractive Lens: Thanks to their special optical design with seven diffractive steps, diffractive lenses enable cataract patients with an artifi cial lens to focus close-up and medium-range as well as over long distances.

A quarter of an hour for clear vision

In the 15-minute operation, which is often performed as outpatient surgery, the clouded lens is fragmented by ultrasound and then removed by suction. An artificial lens, the intraocular lens (IOL) is inserted into the intact capsular bag to restore the patient’s visual acuity. Thanks to a wide choice of different artificial lenses, it is even possible to correct vision defects or astigmatism.

Artificial lenses are made of various materials: plexiglass, silicones or acrylics. "We prefer materials which have been used as implant for 20 years and which have therefore been proven successful in contact with the eye and are absolutely safe," says Christian Fleischmann, Production Manager at HumanOptics. "This is particularly important nowadays as more and more young people are requiring cataract surgery and the artificial lens will have to stay in their eye for many years."

In Erlangen, IOLs are made of hydrophilic acrylate. In its "dry state", this material has similar properties to plexiglass and is therefore easily machinable. As a finished product in a "moist state", however, it is highly flexible and can be folded several times. This has the advantage that only a tiny incision has to be made to insert the lens and this incision heals quickly and often without requiring sutures. HumanOptics has plants in Erlangen and St. Augustin for developing, producing and marketing intraocular lenses for various indications. With its 100 % subsidiary Dr. Schmidt, it has more than 30 years of experience in the IOL sector. "We are one of the few companies in this line of business that can offer the entire vertical range of manufacture", says Fleischmann. HumanOptics commands a particularly strong position in innovative lenses and high-quality standard lenses. The special lens Aspira-aAY, for example, is a leading-edge solution for cataract surgery.

Fragile lenses milled by special machinery

The lenses are pre-contoured on precision turning machines with diamond tools. This is the only stage where they are clamped mechanically in precision chucks. The IOLs are then milled in ultra-precise milling machines. Here, the parts are already clamped in a vacuum before the contour of the lens is milled with diamond milling tools. The next step is finishing on ultra-precise turning machines with specially polished diamond tools, again using vacuum clamping technology. A 10 cent-sized piece of acrylic material is thus gradually turned into a lens with a diameter of 7 mm in polish-free quality. The haptics, i.e. the miniature wires with which the lens is streched in the eye, are only 70 μm thick.

Fig. 2: Working at a magnification of 160x, the staff check the lenses for the tiniest defects.

High magnification, high light yield

The delicate lenses are inspected time and again under a microscope to ensure they meet the highest quality standards and offer the greatest possible safety for the patient. A Leica M205 C stereomicroscope is at hand for precise quality control. "The deciding factor for the choice of this microscope was the high magnification and optimum light yield", says Fleischmann. Working at a magnification of 160x, the staff check the lenses for the tiniest defects, which may be caused in the machining process when particles the size of a few nanometers adhere to the lens or tool and leave marks on the material’s surface.

Quality inspection of tools for special lenses

The Leica stereomicroscope is also used to check the quality of special tools used at the Erlangen plant to produce toric and diffractive lenses. Toric lenses have a special surface design and are used to regulate astigmatism. Diffractive lenses enable cataract patients with an artificial lens to focus close-up and medium-range as well as over long distances.

"This is achieved with a special optical design based on the principle of diffraction", explains Fleischmann. "Our lens has diffractive steps with sharp optical edges. The production tolerances for the step heights are in the order of a few nanometers, roughness in surface quality may be in the subnanometer range." These types of lenses are made of silicone, so the mold has to meet top precision specifications, too – another job for the Leica stereomicroscope.

Fig. 3: Foldable toric intraocular lens
Fig. 4: Microscopic image of the contact between haptic and lens

Long-lasting implants

Before the lenses leave the production line in Erlangen, they are subjected to preliminary cleaning. The staff work in a fl owbox and thus in a dust-free environment. Under the microscope they detect the finest specks of dust and other particles and clean the lenses with soap solution, alcohol and ultra pure water.

At the HumanOptics plant in St. Augustin, the IOLs are cleaned again under cleanroom conditions and measured. The company produces up to 15.000 lenses a month. Central Europe and the German speaking countries are covered by the trade mark Dr. Schmidt. Most of the IOLs with the trade mark HumanOptics are exported worldwide. North, Middle and Eastern Europe, Asia, Australia and the Middle East are key markets for IOLs. "In these countries, quality is a key criterion for special lenses and customers accept that it entails higher cost", says Fleischmann. "Quality has top priority for us, too: after all, our implants are designed to last for decades."

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