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

AIM: To estimate the prevalence of glaucoma among people worldwide. METHODS: Available published data on glaucoma prevalence were reviewed to determine the relation of open angle and angle closure glaucoma with age in people of European, African, and Asian origin. A comparison was made with estimated world population data for the year 2000. RESULTS: The number of people with primary glaucoma in the world by the year 2000 is estimated at nearly 66.8 million, with 6.7 million suffering from bilateral blindness. In developed countries, fewer than 50% of those with glaucoma are aware of their disease. In the developing world, the rate of known disease is even lower. CONCLUSIONS: Glaucoma is the second leading cause of vision loss in the world. Improved methods of screening and therapy for glaucoma are urgently needed.

https://bjo.bmj.com/content/bjophthalmol/80/5/389.full.pdf

Number of people with glaucoma worldwide.

Global prevalence of glaucoma and projections of glaucoma burden through 2040: a systematic review and meta-analysis.

We investigated whether cataract decreases whole-field scotopic sensitivity, a measurement used for the detection of early glaucoma damage. The study population consisted of 33 patients scheduled for cataract surgery. Patients were >/=50 years old and had no ocular disease except senile cataract. The whole-field scotopic sensitivity of one eye of each subject was measured 1 day before and 3 months after cataract surgery. That of six persons of similar age without cataract was also measured twice, 3 months apart. Cataract extraction was associated with significantly improved sensitivity (p = 0.005). With stratification by cataract type, only persons with nuclear sclerosis demonstrated a significantly improved sensitivity after cataract surgery (p = 0.03). The magnitude of sensitivity improvement after surgery did not differ significantly between patients with mild compared to moderate cataract. Multiple regression analysis revealed that age, preoperative intraocular pressure, change in visual acuity, cataract type, and cataract severity were not independently significant predictors of change in sensitivity after cataract surgery. We conclude that cataract may alter the whole-field scotopic sensitivity score and may need to be taken into account in its use for glaucoma screening.

Effect of cataract on a scotopic sensitivity screening test for glaucoma.

Changes in sclera mechanical properties have been shown to play an important role in ocular diseases such as glaucoma 1,2,3 and myopia 4,5. In both diseases, those changes in mechanical behavior were observed along with changes in proteoglycan (PG) and associated glycosaminoglycan (GAG) levels, which have been shown to significantly influence the viscoelastic behavior of other tissues 6.Copyright © 2013 by ASME

The role of glycosaminoglycans in the mechanical behavior of the posterior sclera

Intraocular pressure: relevant or redundant?

Wide variations in the response to intraocular (IOP)-lowering medications may be due to the normal response of the subjects or to variables unrelated to the effect of medication, eg, noncompliance or recording errors. We used data from a previous study of medications designed to lower IOP to investigate the influence of readings showing an unusually large increase in IOP from baseline on the statistical analysis and conclusions. These readings, which could have been due to variables unrelated to the effect of medication, were defined as "outliers" by a statistical method. A statistically insignificant difference between two IOP-lowering medications became significant on excluding two subjects with outlier IOP readings. We explain how reporting results obtained with and without including outliers in the analysis may provide clinicians with more complete information.

"Outlier" intraocular pressure readings: valid or invalid for statistical analysis?

PURPOSE: Retinal thickness (RT) is a useful measurement for describing diseases that affect the thickness of the retina, such as glaucoma. Existing normative data are derived from relatively young individuals; however, glaucoma is most prevalent in older individuals. We therefore studied the RT in older normal individuals. PATIENTS AND METHODS: Participants of the Baltimore Eye Study, persons accompanying patients, and staff were recruited and underwent visual field testing and a comprehensive eye examination by a glaucoma specialist. RT was measured with the retinal thickness analyzer (RTA, Talia Technology) and RT values in specific regions were derived using a custom-designed MatLab program. RESULTS: One hundred and three eyes of sixty-two individuals were studied. Mean age was 61 years. Sixty-six percent were female and 82% were of European descent. The average mean deviation on visual field testing was 0.03 dB and the average pattern SD was 1.51 dB. The mean RT of the entire macula was 159+/-16 microm, and was lowest in the foveal pit and highest in the parafoveal annulus. The average distance from the foveal pit to the thickest point in the parafoveal annulus was 1240+/-138 microm. The mean RT of the entire macula was slightly less in older individuals (slope=-5.7 microm/10 y, P=0.02) but the height of the parafoveal annulus relative to the foveal pit, which is determined by the combined thickness of the parafoveal nerve fibers, ganglion cells, inner plexiform layer, and inner nuclear layer, did not vary with age (P=0.62). CONCLUSIONS: Although the average RT of the entire macula was slightly thinner with increasing age, the height of the parafoveal annulus relative to the foveal pit did not change with age and would therefore seem to be a better marker of neuronal tissue health than the average RT of the entire macula.

Harry A. Quigley

Papers

Effect of cataract on a scotopic sensitivity screening test for glaucoma.

The role of glycosaminoglycans in the mechanical behavior of the posterior sclera

Intraocular pressure: relevant or redundant?

"Outlier" intraocular pressure readings: valid or invalid for statistical analysis?

Retinal thickness in eyes of older normal individuals and its implication for the diagnosis of glaucoma.