Lasers & photonics
This need for small and cheap OCTs is definitely a trend in the medical device industry. Low-cost, portable and easy-to-use OCT systems will be essential in facilitating widespread use in point-of-care settings, although they must ensure that they offer the necessary imaging performances.
The HandheldOCT EU Project was born with the goal of developing a new generation of handheld OCT systems in the 1060nm wavelength region for optimum tissue penetration, with size and cost beyond state-of- the-art. Photonic integrated circuit technology allows us to meet all these requirements, and in this particular case, the chip will also include freeform optics developed by the company Nanoscribe GmbH & Co. KG. Other approaches for saving costs and reducing the size include changes in the spectrometer and the scanning optics, new system control design or the use of 3D-printing technology for non-critical components.
Retinal oximetry
Another interesting diagnostic application of photonics technology is retinal oximetry; that is, the measurement of the haemoglobin in the eye of a patient to assess the amount of oxygen in the bloodstream. Haemoglobin is a protein in the blood that carries oxygen around the bloodstream. It can be used as an indicator of whether a tissue is receiving enough oxygen or not, as any malfunction in the supply of oxygen and nutrients can lead to a variety of diseases. Retinal oximetry is a non-invasive spectrophotometric imaging technique, in which the difference in light absorbance of deoxyhaemoglobin and oxyhaemoglobin is measured. This procedure allows healthcare professionals to detect a lack of oxygen associated with the eyes, such as corneal hypoxia.
“Photonic technologies in ophthalmology and visual sciences are in constant evolution. Several of them have become successful commercial products, and many others are expected to come in the near future.”
Commercial oximeters are based on a stationary fundus camera and they are restricted to patients who can be positioned upright. Some new developments have been performed for supine patients, such as young children, comatose or sedated patients, in cases where measurement of retinal saturation is not possible using current devices. The company Demcon Focal B.V. has developed a handheld, mobile retinal oximeter named Corimap Camera. Apart from the flexibility and mobility, some of its advantages are the use of polarised light (because it could have a beneficial effect
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on the oxygen measurements due to the reduction of vascular reflections) and the reduction of light exposure with the use of infrared light for the alignment, instead of continuous white light. Some clinical trials were recently published, showing that the Corimap Camera prototype is sensitive to oxygen changes in retinal vessels and performs well in comparison with the current standards of retinal oximetry. The ultimate goal is to use this device on prematurely birthed babies to assess the risk of – as well as act to prevent – eye diseases resulting from oxygen therapy used due to the premature development of their lungs.
Visual simulators
In recent years, we have seen an increase in the number of surgeries to implant intraocular lenses in human beings. Providing patients with the visual experience before the treatment is an important factor in their decision to undergo the operation, so several visual simulators have been developed as clinical instruments to demonstrate the effect of different lens designs and to guide the patient and eye care practitioner in the selection of the most suitable correction. These visual simulators use adaptive optics (AO) to introduce virtually any desired aberration profile and to evaluate the patient’s spatial vision for each controlled aberration profile.
AO visual simulators based on deformable mirrors, spatial light modulators or opto-tuneable lenses are increasingly used to simulate vision through different multifocal lens designs. These active optical elements reproduce the equivalent phase map of a certain optical design in a plane conjugate to the subject’s pupil plane, while the observer is looking at a visual stimulus. The visual simulators were initially limited to experimental environments, given their relatively high complexity and dimensions – although some have made their way into commercial products. One example is the SimVis Gekko from the company 2Eyes Vision, developed for the pre-surgical simulation of presbyopia (age-related loss of focus on nearby objects) correction. Another interesting and high potential application for AO visual simulators is related to the understanding the true impact of aberrations on vision. Once ocular aberrations have been correctly measured, the question arises about their influence on vision. There is still some work to be done in this field. Photonic technologies in ophthalmology and visual sciences are in constant evolution. Several of them have become successful commercial products, and many others are expected to come in the near future. Certainly, validation and compliance of the regulations will limit their access to some applications, but they can replace several traditional techniques with all their great advantages. ●
Medical Device Developments /
www.nsmedicaldevices.com
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