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HomeminewsOranges, Lemons and Aspheric Lenses

Oranges, Lemons and Aspheric Lenses

Specsavers has highlighted the vital role that optical dispensers play in providing clear vision to patients for all their needs.

The organisation’s third national Dispensing Conference took place in July with full day presentations delivered to Specsavers and non-Specsavers optical dispensers in Perth, Melbourne, Brisbane, and Sydney.

This year’s conference enabled local dispensers to learn from global experts, among them Professor Mo Jalie and Alicia Thompson.

Closed questions are also essential to control the duration of conversation

Professor Jalie, who has written some of the core texts for optical dispensing education and owns numerous patents for lens designs, delivered the keynote on aspheric lenses.

Commencing the lecture with discussion about the importance of understanding off-axis lens design he said, “As students we are taught about what happens when the eye looks through the centre of the lens, but we are not often taught about what happens when the eye turns and looks through the edge.”

Prof Jalie continued by advising that an ideal lens would have a power of +4, no matter which zone was being looked through. For the best formed lens, the power must remain as close as possible to the on-axis power as it does when the eye rotates into off-axis zones.

Professor Jalie went on to discuss aspherical surfaces, how they work and how aspheric lenses are designed, manufactured and fitted, taking into account off-axis powers associated with ocular rotation.

The basic conicoidal surfaces used for most low powered aspheric lenses – ellipsoidal, parabaloidal, hyperboloid – were aptly explained using the analogy of cutting into an orange (sphere) and a lemon (ellipsoid). How you grind the lens will alter its shape and curve, and in doing so, the way in which light passes through the lens.

In essence, aspherical surfaces are astigmatic and they work because by changing the asphericity, you are changing the astigmatism of the surface. You can use surface astigmastism to neutralise the effects that we get when light passes obliquely through a lens.

Professor Jalie described aspherical lenses as mechanically superior – they are thinner, lighter, and more attractive because of smaller magnification; and they are state of the art – which is what customers expect.

He explained that they “come into their own” when working with medium to strong prescriptions and are the only way to attack astigmatism for strong plus lenses – the most severe aberration for a spectacle lens wearer.

Cosmetically they are better – they are flat so they produce less magnification. Additionally, they can be personalised – by feeding the parameters you want into the computer when setting up the lens generator, you can change the vertex distance, the pantoscopic tilt, and the face form angle.

However, he cautioned, we don’t know how a lens is going to behave in front of the eye unless we know how it’s fitted – the wearer’s facial characteristics as well as the frame the lens is fitted to (and therefore the size and shape of the lens) will all alter the performance of the lens on and off axis.


Alicia Thompson, from the Association of British Dispensing Opticians, addressed the importance of clear communication when gathering and imparting information, in an effort to deliver optimum results.

With so many lens designs and coatings now available, assuming a patient’s needs based on their age, gender or demographic, or taking a ‘one size fits all’ approach to dispensing is not appropriate, she said. Optical dispensers must be able to gather information correctly about the patient before determining the most appropriate lens design, and communicate the reasons for their recommendation correctly so that patients are informed and part of the decision making process.

Gathering information should involve a series of open questions, for example, “tell me about you?, what does your day involve, and what are your visual needs?” Closed questions are also essential to control the duration of conversation. Explore the patient’s emotions and concerns, listening actively with eye contact, and observing their body language for additional signals. Above all, show empathy – although practices see people with multiple vision problems every day, the patient only sees their own and they may need support.

Ms Thompson said the art to recommending lens options is to explain the features and benefits, as well as the limitations of each. In this way, the patient does not feel they are being ‘sold’ but instead they are part of the decision making process.

Setting realistic expectations about the lens, particularly if the patient is new to prescription lenses or being prescribed a significantly different lens, will lessen the likelihood of them returning to the practice with a complaint.