A technique called optical coherence tomography (OCT) has been developed for noninvasive cross-sectional imaging in biological systems. OCT uses low-coherence interferometry to produce a two-dimensional image of optical scattering from internal tissue microstructures in a way that is analogous to ultrasonic pulse-echo imaging. OCT has longitudinal and lateral spatial resolutions of a few micrometers and can detect reflected signals as small as approximately 10(-10) of the incident optical power. Tomographic imaging is demonstrated in vitro in the peripapillary area of the retina and in the coronary artery, two clinically relevant examples that are representative of transparent and turbid media, respectively.

/pdf/optical-coherence-tomography-3zqbp7mpwb.pdf

Optical coherence tomography

Aim: To estimate the number of people with open angle (OAG) and angle closure glaucoma (ACG) in 2010 and 2020. Methods: A review of published data with use of prevalence models. Data from population based studies of age specific prevalence of OAG and ACG that satisfied standard definitions were used to construct prevalence models for OAG and ACG by age, sex, and ethnicity, weighting data proportional to sample size of each study. Models were combined with UN world population projections for 2010 and 2020 to derive the estimated number with glaucoma. Results: There will be 60.5 million people with OAG and ACG in 2010, increasing to 79.6 million by 2020, and of these, 74% will have OAG. Women will comprise 55% of OAG, 70% of ACG, and 59% of all glaucoma in 2010. Asians will represent 47% of those with glaucoma and 87% of those with ACG. Bilateral blindness will be present in 4.5 million people with OAG and 3.9 million people with ACG in 2010, rising to 5.9 and 5.3 million people in 2020, respectively. Conclusions: Glaucoma is the second leading cause of blindness worldwide, disproportionately affecting women and Asians.

The number of people with glaucoma worldwide in 2010 and 2020

Optical coherence tomography (OCT) has developed rapidly since its first realisation in medicine and is currently an emerging technology in the diagnosis of skin disease. OCT is an interferometric technique that detects reflected and backscattered light from tissue and is often described as the optical analogue to ultrasound. The inherent safety of the technology allows for in vivo use of OCT in patients. The main strength of OCT is the depth resolution. In dermatology, most OCT research has turned on non-melanoma skin cancer (NMSC) and non-invasive monitoring of morphological changes in a number of skin diseases based on pattern recognition, and studies have found good agreement between OCT images and histopathological architecture. OCT has shown high accuracy in distinguishing lesions from normal skin, which is of great importance in identifying tumour borders or residual neoplastic tissue after therapy. The OCT images provide an advantageous combination of resolution and penetration depth, but specific studies of diagnostic sensitivity and specificity in dermatology are sparse. In order to improve OCT image quality and expand the potential of OCT, technical developments are necessary. It is suggested that the technology will be of particular interest to the routine follow-up of patients undergoing non-invasive therapy of malignant or premalignant keratinocyte tumours. It is speculated that the continued technological development can propel the method to a greater level of dermatological use.

https://link.springer.com/content/pdf/bfm%3A978-3-319-06419-2%2F1.pdf

Optical Coherence Tomography

https://www.thelancet.com/pdfs/journals/lancet/PIIS0140-6736(07)61690-0.pdf

Maternal and child undernutrition: global and regional exposures and health consequences

https://www.thelancet.com/pdfs/journals/lancet/PIIS0140-6736(13)60937-X.pdf

Maternal and child undernutrition and overweight in low-income and middle-income countries

Vitamin A and measles vaccination.

The duration of the effect of vitamin A supplementation.

Aberrant dark adaptation is common to many ocular diseases and pathophysiological conditions, including vitamin A deficiency, cardiopulmonary diseases, and hypoxia. Scotopic vision and pupillary responsiveness have typically been measured using subjective, time-consuming methods. Existing techniques are particularly challenging for use in developing country settings, where vitamin A deficiency remains a major public health problem. Our aim was design a compact, low cost, and easily operated device to assess dark adaptation in the field. The Portable Field Dark Adaptometer (PFDA) incorporates a digital camera, a retinal bleaching flash, and a Ganzfeld light source inside a pair of light-obscuring goggles. After a ~10 min period of dark adaption, the infrared camera digitally records afferent pupillary responses to graded light stimuli (−2.9 to 0.1 log cd/m2). We tested this device in a variety of field settings to assess: a) ease of use and b) whether test data could clearly and accurately depict the well-known dose-response relationship between light intensity and pupil contraction. A total of 822 videos were collected. We used an open source video analysis software to measure pupil size in pixel units. Pupillary responsiveness was expressed as the percent change in pupil size from pre- to post-light exposure. Box plots, t test, and multi-level mixed effects linear regression modeling were used to characterize the relationship between light intensity and pupillary response. The PFDA was employed with only minor technical challenges in Bangladesh, Kenya, Zambia, and Peru. Our data show a clear linear increase in pupillary constriction with increasing log light intensity. Light intensity was a strong predictor of pupillary response, regardless of baseline pupil size. The consistent physiological response demonstrated here supports the use of the PFDA as a reliable tool to measure dark adaptation. As a next step, PFDA measurements will be validated against biochemical indicators of vitamin A status and hypoxemia. Ultimately, this new technology may provide a novel approach for nutritional assessment, with potential clinical applications.

/pdf/a-novel-device-for-assessing-dark-adaptation-in-field-2c30a8211s.pdf

A novel device for assessing dark adaptation in field settings

A randomized trial tested whether a priming dose of vitamin A would extend the protection of a subsequent 60,000-micrograms retinol equivalent (RE) oral dose Seventy-five xerophthalmic and 74 age- and neighborhood-matched non-xerophthalmic preschool children were randomized to one of three oral regimens of vitamin A, receiving peanut oil only (Group A), 7500 micrograms RE (Group B) or 60,000 micrograms RE (Group C), followed in all instances by 60,000 micrograms RE 1 wk later Serum retinol was measured 2, 4, 6 and 12 mo following the second dose by technicians unaware of the children's treatment status Among xerophthalmic children, mean values differed across treatment groups at 2 mo (C > A) and tended to be different at 12 mo (C > A and B > A) Among non-xerophthalmic children mean retinol concentrations differed across treatment groups at 6 mo, but not in a consistent way (A > C > B), and at 12 mo (C > A and B > A) Xerophthalmic children reverted to biochemical deficiency faster than non-xerophthalmic children A small or large priming dose may extend the protection conferred by a 60,000-micrograms RE dose, supporting the use of repeated, spaced doses of vitamin A for treating xerophthalmia Similar retinol concentrations in Groups B and C at 12 mo suggest the 60,000-micrograms RE prophylactic dose currently recommended by the World Health Organization need not be increased

A priming dose of oral vitamin A given to preschool children may extend protection conferred by a subsequent large dose of vitamin A

Anecdotal and historical data strongly suggest that environmental factors and hygienic practices play a major role in chlamydial transmission and the maintenance of endemic blinding trachoma. They also suggest that relatively minor alterations in these practices can have a profound impact, virtually eliminating trachoma as a blinding disease. This is especially critical, since few countries can now afford extensive, ongoing chemoprophylaxis programs. Epidemiologic studies are now needed to identify the critical risk factors in each affected culture. A recent study that used this approach found that in one region the simple hygienic practice of face washing was strongly associated with trachoma status. The next task will be to carry out appropriately designed intervention trials to establish the significance of such a factor and the possibility of altering it.

https://www.jstor.org/stable/info/4453741

Alfred Sommer

Papers

Vitamin A and measles vaccination.

The duration of the effect of vitamin A supplementation.

A novel device for assessing dark adaptation in field settings

A priming dose of oral vitamin A given to preschool children may extend protection conferred by a subsequent large dose of vitamin A

Risk-Factor Studies as an Epidemiologic Tool