Multispectral imaging of the ocular fundus using light emitting diode illumination

We present an imaging system based on light emitting diode (LED) illumination that produces multispectral optical images of the human ocular fundus. It uses a conventional fundus camera equipped with a high power LED light source and a highly sensitive electron-multiplying charge coupled device camera. It is able to take pictures at a series of wavelengths in rapid succession at short exposure times, thereby eliminating the image shift introduced by natural eye movements (saccades). In contrast with snapshot systems the images retain full spatial resolution. The system is not suitable for applications where the full spectral resolution is required as it uses discrete wavebands for illumination. This is not a problem in retinal imaging where the use of selected wavelengths is common. The modular nature of the light source allows new wavelengths to be introduced easily and at low cost. The use of wavelength-specific LEDs as a source is preferable to white light illumination and subsequent filtering of the remitted light as it minimizes the total light exposure of the subject. The system is controlled via a graphical user interface that enables flexible control of intensity, duration, and sequencing of sources in synchrony with the camera. Our initial experiments indicate that the system can acquire multispectral image sequences of the human retina at exposure times of 0.05 s in the range of 500-620 nm with mean signal to noise ratio of 17 dB (min 11, std 4.5), making it suitable for quantitative analysis with application to the diagnosis and screening of eye diseases such as diabetic retinopathy and age-related macular degeneration.

Internal quantum efficiency and tunable colour temperature in monolithic white InGaN/GaN LED

Internal Quantum Efficiency (IQE) of two-colour monolithic white light emitting diode (LED) was measured by temperature dependant electro-luminescence (TDEL) and analysed with modified rate equation based on ABC model. External, internal and injection efficiencies of blue and green quantum wells were analysed separately. Monolithic white LED contained one green InGaN QW and two blue QWs being separated by GaN barrier. This paper reports also the tunable behaviour of correlated colour temperature (CCT) in pulsed operation mode and effect of self-heating on device performance. © 2014 SPIE.

Superior color rendering with a phosphor-converted blue-cyan monolithic light-emitting diode

The future generation of modern illumination should not only be cheap and highly efficient, but also demonstrate high quality of light, light which allows better color differentiation and fidelity. Here we are presenting a novel approach to create a white solid-state light source providing ultimate color rendition necessary for a number of applications. The proposed semi-hybrid device combines a monolithic blue-cyan light emitting diode (MBC LED) with a green-red phosphor mixture. It has shown a superior color rendering index (CRI), 98.6, at correlated color temperature of around 3400 K. The MBC LED epi-structure did not suffer from the efficiency reduction typical for monolithic multi-color emitters and was implemented in the two most popular chip designs: “epi-up” and “flip-chip”. Redistribution of the blue and cyan band amplitudes in the white-light emission spectrum, using the operating current, is found to be an effective tool for fine tuning the color characteristics. (Figure presented.).

A randomised controlled trial investigating the effect of lutein and antioxidant dietary supplementation on visual function in healthy eyes

Background & aims It has been suggested that retinal lutein may improve visual acuity for images that are illuminated by white light. Our aim was to determine the effect of a lutein and antioxidant dietary supplement on visual function. Methods A prospective, 9- and 18-month, double-masked randomised controlled trial. For the 9-month trial, 46 healthy participants were randomised (using a random number generator) to placebo (n=25) or active (n=21) groups. Twenty-nine of these subjects went on to complete 18 months of supplementation, 15 from the placebo group, and 14 from the active group. The active group supplemented daily with 6mg lutein combined with vitamins and minerals. Outcome measures were distance and near visual acuity, contrast sensitivity, and photostress recovery time. The study had 80% power at the 5% significance level for each outcome measure. Data were collected at baseline, 9, and 18 months. Results There were no statistically significant differences between groups for any of the outcome measures over 9 or 18 months. Conclusion There was no evidence of effect of 9 or 18 months of daily supplementation with a lutein-based nutritional supplement on visual function in this group of people with healthy eyes. ISRCTN78467674.

Anterior eye health recording

Aims: To survey eye care practitioners from around the world regarding their current practice for anterior eye health recording to inform guidelines on best practice. Methods: The on-line survey examined the reported use of: word descriptions, sketching, grading scales or photographs; paper or computerised record cards and whether these were guided by proforma headings; grading scale choice, signs graded, level of precision, regional grading; and how much time eye care practitioners spent on average on anterior eye health recording. Results: Eight hundred and nine eye care practitioners from across the world completed the survey. Word description (p <. 0.001), sketches (p = 0.002) and grading scales (p <. 0.001) were used more for recording the anterior eye health of contact lens patients than other patients, but photography was used similarly (p = 0.132). Of the respondents, 84.5% used a grading scale, 13.5% using two, with the original Efron (51.6%) and CCLRU/Brien-Holden-Vision-Institute (48.5%) being the most popular. The median features graded was 11 (range 1-23), frequency from 91.6% (bulbar hyperaemia) to 19.6% (endothelial blebs), with most practitioners grading to the nearest unit (47.4%) and just 14.7% to one decimal place. The average time taken to report anterior eye health was reported to be 6.8. ±. 5.7. min, with the maximum time available 14.0. ±. 11. min. Conclusions: Developed practice and research evidence allows best practice guidelines for anterior eye health recording to be recommended. It is recommended to: record which grading scale is used; always grade to one decimal place, record what you see live rather than based on how you intend to manage a condition; grade bulbar and limbal hyperaemia, limbal neovascularisation, conjunctival papillary redness and roughness (in white light to assess colouration with fluorescein instilled to aid visualisation of papillae/follicles), blepharitis, meibomian gland dysfunction and sketch staining (both corneal and conjunctival) at every visit. Record other anterior eye features only if they are remarkable, but indicate that the key tissue which have been examined.

Discrimination of healthy and cancer cells of the bladder by metabolic state, based on autofluorescence

Bladder cancer is among the most common cancers worldwide (4th in men). It is responsible for high patient morbidity and displays rapid recurrence and progression. Lack of sensitivity of gold standard techniques (white light cystoscopy, voided urine cytology) means many early treatable cases are missed. The result is a large number of advanced cases of bladder cancer which require extensive treatment and monitoring. For this reason, bladder cancer is the single most expensive cancer to treat on a per patient basis. In recent years, autofluorescence spectroscopy has begun to shed light into disease research. Of particular interest in cancer research are the fluorescent metabolic cofactors NADH and FAD. Early in tumour development, cancer cells often undergo a metabolic shift (the Warburg effect) resulting in increased NADH. The ratio of NADH to FAD ("redox ratio") can therefore be used as an indicator of the metabolic status of cells. Redox ratio measurements have been used to differentiate between healthy and cancer breast cells and to monitor cellular responses to therapies. Here, we have demonstrated, using healthy and bladder cancer cell lines, a statistically significant difference in the redox ratio of bladder cancer cells, indicative of a metabolic shift. To do this we customised a standard flow cytometer to excite and record fluorescence specifically from NADH and FAD, along with a method for automatically calculating the redox ratio of individual cells within large populations. These results could inform the design of novel probes and screening systems for the early detection of bladder cancer.

Cost-effective optical coherence tomography spectrometer based on a tilted fiber Bragg grating

A compact, fiber-based spectrometer for biomedical application utilizing a tilted fiber Bragg grating (TFBG) as integrated dispersive element is demonstrated. Based on a 45° UV-written PS750 TFBG a refractive spectrometer with 2.06 radiant/μm dispersion and a numerical aperture of 0.1 was set up and tested as integrated detector for an optical coherence tomography (OCT) system. Featuring a 23 mm long active region at the fiber the spectrum is projected via a cylindrical lens for vertical beam collimation and focused by an achromatic doublet onto the detector array. Covering 740 nm to 860 nm the spectrometer was optically connected to a broadband white light interferometer and a wide field scan head and electronically to an acquisition and control computer. Tomograms of ophthalmic and dermal samples obtained by the frequency domain OCT-system were obtained achieving 2.84 μm axial and 7.6 μm lateral resolution. © 2014 SPIE.