Coma aberration

Pearl No. 4: Measurements of spherical aberrations of the anterior corneal surface have found the average value to be 0.27 μm with a large standard deviation of 0.10 μm. Due to this variation, the value should be measured for each individual patient.3

How can you recognize the ZEISS DriveSafe coating? The ZEISS DriveSafe coating is evident from a slightly violet residual reflection on the lens, which is barely visible and therefore not distracting.

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Pearl No. 12: Negative aspheric IOLs have a slightly higher power centrally. For a 20.00 D lens, this power can be 0.50 D greater and, thus, provides some pseudoaccommodative effect. This is one explanation for increased near vision in patients implanted with aspheric IOLs.

Pearl No. 10: Refractive error can compensate for residual spherical aberration. Positive spherical aberration causes a myopic shift, and negative spherical aberration causes a hyperopic shift in refraction. Although refractive error is independent of pupil size, spherical aberration is dependent on pupil size; for small pupils, it can be negligible, but for larger pupils it is significant in its effect. Thus, refractive error will compensate for spherical aberration at larger pupil sizes but will introduce defocus at smaller pupil sizes (Figure 4). This information can be used to customize results for individual patients based on the choice of aspheric IOL.7

Pearl No. 8: The impact of spherical aberration is dependent on pupil size. For practical purposes, spherical aberration comes into play when pupils are greater than 4 mm; thus, it has the most impact under mesopic or scotopic conditions and in younger patients. Older individuals may have large pupils, so pupils should be measured for each patient if aspheric IOLs are to be used.

Special coatings with a hard lacquer matched to the material not only enhance the scratch resistance of the lenses, they also ensure constant visual quality and extend durability. Thanks to the DuraVision®  Platinum coating, ZEISS offers a solution that is three times harder than the previous generation of hard (AR) coated plastic ZEISS lenses and 35% harder than AR coated mineral (glass) ZEISS lenses. This is made possible by the way ions seal the lens when the coating is applied.  Read on to find out more.

Lenses can help protect your eyes against blue light thanks to a special filter, making it easier to work at a computer or use digital devices. Thanks to DuraVision® BlueProtect from ZEISS, you receive a premium lens coating together with a blue light filter, which is great for all wearers who are often indoors and find that the light emitted by LED light bulbs, TVs or computer monitors makes them tired or uncomfortable. It is therefore advisable to opt for this lens coating, even for glasses you need for work or when watching TV.

With DuraVision DriveSafe, 64% of wearers tested said they experienced fewer problems with glare thanks to the new coating compared to other premium anti-reflective coatings. Source: Internal wearer trial (CZV employees in Germany), external wearer trial (eye care professionals and consumers in Spain)

Sphericalaberration

Pearl No. 2: The wavefront of the human eye can be measured using wavefront analyzers such as Shack- Hartmann systems and Tracey aberrometers (iTRACE; Tracey Technologies, Corp.). Corneal topographers can measure the front surface of the cornea (Figure 1), and this data can be transformed to determine the HOAs of the cornea. By convention, corneal spherical aberration is measured at 6 mm.1

Chromatic aberration

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Radialdistortion

A premium lens coating can help, one that’s integrated into the  ZEISS DriveSafe lenses. This reduces the subjective sensation of glare1 – e.g. from oncoming vehicles with LED or Xenon headlights – and effectively protects your lenses from both scratches and the adhesion of dirt particles.

Lendistortion

Unfortunately, no coating will mean never having to clean lenses again. However, lenses can be coated in such a way that impurities are less likely to adhere to the lens. CleanCoat makes the lens surface smooth, making it more difficult for dirt and dust to adhere. This simplifies lens care tremendously. The smoother the lens surface, the better.

Just ask your optician. Choosing the right coating also matters if you’re buying children’s glasses or a second pair for yourself – so don’t leave this important decision to chance!

George H.H. Beiko, BM, BCh, FRCSC, is an Assistant Professor of Ophthalmology at McMaster University and a Lecturer at the University of Toronto, Canada. Dr. Beiko states that he is a consultant to Abbott Medical Optics Inc. He may be reached at e-mail: george.beiko@ sympatico.ca.

Our vision has changed enormously now that we use digital devices such as smartphones, tablets, and modern illumination through LEDs and displays. We are subjected to more blue light than ever – all day long, in fact. High-energy blue light is also believed to have a negative impact on vision over the long term.

Lens coatings act as a protective coating for your lenses, transforming modern plastic lenses into strong everyday objects. Unfortunately, lens coatings are often not given the importance they deserve when people purchase a pair of glasses, with wearers pretty much leaving this decision up to the optician. To make sure you’re well-prepared when it comes to anti-reflective, hard, CleanCoat and other coatings, we’ve put together a guide to help you find your way around the maze of coatings. After all, the choice is yours!

Lensdistortioncorrection

Anti-reflective lenses can be recognized by the residual reflection. Regardless of the material used for the lenses, they have a characteristic colour when you hold the glasses at a slight angle against a white background. This is highly practical for the wearer: the optician can identify the anti-reflective coating and even offer the same high quality if a switch to another material is desired.

Lenses without an anti-reflective coating have a great disadvantage:  There is a lot of visible reflection for the wearer. These reflections are particularly distracting on wet roads or when driving at night, but also when talking to someone as that person will see themselves reflected in your glasses rather than look at you.

It enables transparent, clear and unimpaired vision, makes glasses more attractive and permits uninterrupted and reflection-free vision for the wearer.

It’s all about protecting your eyes from the sun and glare when you’re outdoors. You and your optician can create your ideal sunglasses in terms of both colour and style. Coloured coatings for sunglasses are available for plastic and mineral lenses. A  wide selection of lens tints  – from single colours and gradient tints to bi-colour or even special tints for medical purposes – feature in the range of sunglasses from ZEISS. So your glasses, whether single vision or progressive lenses, will become your favourite accessory that also delivers first-class protection against the sun.

Just like a lotus leaf, water beads right off thanks to the wetting properties of the coating. A great bonus, particularly for anti-reflective lenses, because you’re more likely to notice dirt through improved reflection reduction than on lenses without such a coating.

Pearl No. 15: Leaving spherical aberration (positive or negative) in the optical system improves depth of focus, but at the cost of loss of contrast vision. Current strategies involve targeting up to -0.30 to -0.40 µm of spherical aberration in one eye, so as to increase depth of focus without significantly affecting Snellen acuity.

Pearl No. 9: The clearest image is provided when the total spherical aberration value for the eye is 0.00. Most of the effect of targeting this value is seen in nighttime lighting conditions (Figure 3).6

Perspectivedistortion

We’ve all been there: Unpleasant glare from oncoming traffic or street lights impairing our vision. This is tiring for drivers and can even become dangerous.

Self-tinting lenses are a great idea for anyone who doesn’t want to change their glasses in the sun as these lenses incorporate a special technology which adapts to the sun – e.g.  PhotoFusion X by ZEISS

Pearl No. 6: In cataract surgery, targeting emmetropia has a greater effect on Snellen acuity outcome than manipulating spherical aberration. Thus, surgeons should first optimize their formulas for IOL power calculation before adjusting spherical aberration. Aspheric IOLs improve the quality of vision by providing greater contrast sensitivity, not by increasing Snellen acuity. An increase in spherical aberration away from 0.00 causes a decrease in contrast sensitivity.4

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Pearl No. 13: Corneal spherical aberration and Q value are not the same thing. Spherical aberration describes how a wavefront deviates from the ideal after passing through a refracting surface. In actuality, it is a measure of the effect a surface has on light and is measured in microns. The Q value describes the refracting surface and is a measure of the shape of a surface; it has no units. The shape of a surface does affect spherical aberration. An ideal spherical surface has a Q value of 0.00. A prolate surface has a negative Q value; a parabola is a prolate surface that eliminates all spherical aberration and has a Q value of -0.50. The human cornea has an average Q value of -0.26; it would require a value of -0.52 to eliminate all spherical aberration. The Q value of a young adult crystalline lens is -0.25; thus, the combined value for a young phakic eye results in elimination of spherical aberration. As the lens ages, the Q value changes, and after age 40 is 0.00. With a perfect single refracting surface such as an ellipse, keratometry and Q value could be used to calculate the spherical aberration of that surface. For a corneal Q value of -0.26 and average keratometry of 44.00 D, the calculated spherical aberration is 0.18 μm. The average measured spherical aberration of the cornea is 0.27 μm because the cornea has a complex surface that is steeper centrally. Common aspheric IOLs correct the average theoretical corneal spherical aberration, the average measured corneal spherical aberration, or do not influence it.

For plastic lenses (organic lenses) you definitely need a hard lacquer coating. While plastic lenses are easy to wear, the material used is softer and more prone to scratches than glass lenses (a.k.a. mineral lenses) – at least if untreated.

Pearl No. 14: Tilt and decentration affect the performance of aspheric IOLs. Aspheric lenses must be decentered more than 0.8 mm and tilted more than 10° before all effect is lost.8

So why not talk to your optician about the anti-reflective coating services on offer and about the coatings’ durability today! Ask for their tips about what you need to look out for to ensure your coating lasts as long as it ought to.

Formerly only needed when the sun was shining brightly, sunglasses with a  mirror coating  are now very much in vogue – and they’re available in your prescription! Talk to your optician today to see the wide range of colours and functions available for sunglass coatings.

Lens manufacturers want to make it easy for their customers to select a coating, which is why they offer packages for different coatings. And ZEISS is no exception: with the  DuraVision®  Premium lens coatings, you receive a complete package comprising top anti-reflective, hard, antistatic and CleanCoat coatings.

Pearl No. 1: The wavefront characteristics of light can be described in mathematical terms using different systems, including Zernike polynomials and Fourier analysis. Using Zernike polynomials, sphere (defocus) and cylinder (astigmatism) describe the two higher-order aberrations (HOAs) that we measure with phoropters. These aberrations account for approximately 83% of the magnitude of the wavefront of light. Spherical aberration and coma are the next most significant HOAs. Spherical aberration describes the amount of bending that occurs as light passes through a refracting surface, such as the cornea, and compares the relative position of the focal points for the peripheral and central light beams. Positive spherical aberration occurs when the peripheral rays are focused in front of the central rays; this value is expressed in microns.

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The residual reflection is usually green. The modern Duravion®  Premium lens Coating from ZEISS has an attractive, bluish residual reflection. The barely perceptible bluish residual reflection increases the amount of light the lens transmits to your eyes. And not only that – the blue is less visible to the eye. This means lenses with this residual reflection have the advantage of making your eyes look clearer to other people and have fewer reflections. Your eyes look more natural, almost as if you’re not wearing glasses at all.

Pearl No. 3: In the human eye, HOAs come primarily from the anterior corneal surface and the lens; other sources are the posterior corneal surface and the retina. In an aphakic eye, the anterior corneal surface accounts for 98% of wavefront changes. Small-incision (less than 2.8 mm) cataract surgery causes minimal changes in the spherical aberration of the eye and, for practical terms, can be considered to have no effect.2

Pearl No. 7: Using aspheric IOLs improves driving safety due to improved contrast sensitivity. This is particularly evident on nighttime simulation testing, in which up to a 45-foot advantage in stopping distance at 55 mph (88.51 km/hr) can be achieved.5

One thing’s for sure: Light has a considerable effect on managing our internal body clock, and thus our sleep patterns. Strong light in the early evening tells your body to stay awake for longer. When you look at the screen on your computer or another digital device, you subject your eyes to large quantities of blue light, causing such things as reduced contrast sensitivity. Focusing on a screen can also be strenuous for you and your eyes, and contribute to digital eye strain.

Pearl No. 5: The presence of spherical aberrations can cause glare and halo around lights. The greater the degree of spherical aberration, the greater amount of halo that is induced (Figure 2).

Another coating level with antistatic function can also help keep your glasses cleaner: fluff – from clothes, for example – adheres to these lenses much less.