many optical qualities: an even illumination of the retina, a large depth of field, no ghosts of flare, high optical resolution and no optical distortions. Also, the quality of the internal optical filters can make a huge difference in the final image quality.’
Wavefront analysis For detecting vision defects such as wavefront aberrations, which are optical imperfections of the eye that prevent light from focusing properly on the retina, camera-based systems can be used for wavefront analysis. Using the Shack-Hartmann technique
− one of the diagnostic principles used to detect aberrations − a laser beam is used to illuminate the ocular fundus. Aſter passing through the lens, the reflected light is focused on a CCD sensor outside of the eye by a lens array. Te generated pixels are then compared to reference points of an ideal imaging lens, allowing the wavefront defects to be quantified in a wavefront chart. Alternatively, for the
Tscherning principle, a series of light spots are applied to the retina, rather than a single beam of light. Te image of the projected pattern is recorded by a camera and also compared with an ideal image to draw conclusions about the eye’s aberrations. Apart from image quality, it is the speed
measurement, and guidance system, which is used to produce a three-dimensional model of each individual patient’s eye prior to surgery, in order to ensure precise delivery of laser pulses. Te camera rotates and captures anterior segment imaging and biometry at two different angles at up to eight different positions around the optical axis, for a total of 16 potential images. Multiple scans identify the precise location of the relevant anatomical structures from the anterior cornea to the posterior capsule. Using these images, as well as optical ray-tracing and biometric data, the augmented reality system creates the 3D model of the eye. Image quality is particularly important
The procedure
involves taking images of both eyes in colour, and also in red to make blood vessels appear dark
of a camera that enables these techniques, explained Volker Zipprich-Rasch, head of marketing and product management at the Baumer Vision Competence Centre: ‘With the Shack-Hartmann principle, you have to apply several hundred light spots, one aſter the other, as fast as you can. So, you project the light beam, take an image, and then scan point-by- point the entire area of the eye,’ he said. ‘It is the camera that is controlling the illumination, so the faster the camera, the faster the entire measurement.’ Baumer’s TX Series cameras are used for wavefront analysis of the eye.
Monitoring surgery But cameras are used beyond diagnostic applications. Last year, Adimec partnered with Lensar to provide technology to cataract surgeons, which included the Lensar Laser System, a femtosecond laser built for refractive cataract surgery. Adimec’s Quartz Qs-4A60 camera is part of the laser’s augmented reality 3D imaging,
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when surgeons rely on the images to make medical decisions, commented Adimec’s Joost van Kuijk: ‘We have identified, besides of course resolution and speed of the imaging, 28 different parameters of what determines the image quality,’ he said. ‘Tat ranges from sensitivity to uniformity and so on, so trying to get the best out of the image sensors on the market.’ But, as medical professionals
typically spend years assessing patients using older, conventional imaging technologies, camera manufacturers should take this is into account when developing
cameras for this market, Van Kuijk added. ‘Sometimes you have to downgrade the possible image quality to be similar to what the surgeons are used to, because they make decisions based on experience, and it takes years to become a good surgeon,’ he pointed out. ‘Even if you introduce a new technology that can do more, you don’t want to change the visual experience of the experienced user, because it will take many years for them to adjust to an even better image to draw conclusions from it. ‘Te system doesn’t draw conclusions, it’s
the person – the experienced pathologist or surgeon that makes decisions based on the image – so it has to be consistent to what they’re used to and what they’re trained on.’ Both eye examinations and the diagnosis
of vision defects or diabetes-related diseases are simple and minimally invasive; even minor eye surgeries, such as cataracts, can be carried out the same day. Terefore, many ophthalmologic procedures are carried out in a standard exam room or an outpatient clinic, which drives a demand for low-cost medical
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