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 characterized the structural and mechanical changes after experimental digestion of sulfated glycosaminoglycans (s-GAGs) in the human posterior sclera, using ultrasound thickness measurements and an inflation test with three-dimensional digital image correlation (3D-DIC). Each scleral specimen was first incubated in a buffer solution to return to full hydration, inflation tested, treated in a buffer solution with chondroitinase ABC (ChABC), then inflation tested again. After each test series, the thickness of eight locations was measured. After enzymatic treatment, the average scleral thickness decreased by 13.3% (p < 0.001) and there was a stiffer overall stress-strain response (p < 0.05). The stress-strain response showed a statistically significant increase in the low-pressure stiffness, high-pressure stiffness and hysteresis. Thus, s-GAGs play a measurable role in the mechanical behaviour of the posterior human sclera.

https://royalsocietypublishing.org/doi/pdf/10.1098/rsif.2016.0367

The contribution of glycosaminoglycans to the mechanical behaviour of the posterior human sclera.

Purpose

The collagen structure of the human peripapillary sclera plays a significant role in determining optic nerve head (ONH) biomechanics, and is therefore of interest in the study of glaucoma. The aim of the current work was to map the anisotropic collagen structure of the normal human peripapillary sclera as a function of tissue depth.

Methods

Wide-angle x-ray scattering was used to quantify collagen fibril orientation at 0.5mm intervals across six 150μm-thick serial sections through the peripapillary sclera of eight normal European-derived human eyes. Two structural parameters were measured: 1) the relative number of fibrils preferentially aligned at a given angle within the tissue plane, 2) the degree of collagen alignment (anisotropy).

Results

The inner-most one-third of the peripapillary scleral stroma (nearest to the choroid) was characterised by collagen fibrils either randomly arranged or preferentially aligned radially with respect to the ONH. In contrast, the outer two-thirds of the tissue was dominated by a circumferential arrangement of collagen encircling the ONH. In all tissue regions the degree of collagen anisotropy peaked in the mid-stroma and progressively decreased towards the tissue surfaces, with the largest depth variations occurring in the inferior-nasal quadrant, and the smallest occurring in the superior-nasal quadrant.

Conclusions

Significant, region-specific variations in collagen structure are present in the human peripapillary sclera as a function of depth. In normal eyes, the circumferential collagen fibril architecture is most prominent in the outer two-thirds of the stroma, possibly as a mechanical adaption to more effectively support the lamina cribrosa at the level of its insertion into the scleral canal wall.

Depth-Dependent Changes in Collagen Organization in the Human Peripapillary Sclera

Thirty-four patients with glaucoma were treated with the Ocusert pilocarpine system, a unique method of providing round-the-clock delivery of pilocarpine in the eye for seven-day periods. Advantages of the device include therapeutic effectiveness and continuous release rate, less effect on accommodation, less miosis, convenience for the patient, and reliability in patients who must rely on others for treatment (eg, children and the elderly). Some disadvantages encountered were need for instruction and encouragement of patients; retention difficulties, with some patients unaware when the device was lost; occasional side effects of a cutting sensation (as when the Ocusert sometimes doubles over), movement in the eye, and transient blurring of vision and miosis; and high cost. Overall, when compared to pilocarpine eyedrops, the Ocusert pilocarpine system presents many definite advantages and is a highly desirable method of therapy in selected cases of glaucoma.

The Ocusert pilocarpine system: advantages and disadvantages

Dellen may occur in the corneas of eyes with filtering blebs. Nine cases of such dellen were encountered in a series of 97 consecutive trabeculectomies. In two such patients, the dell progressed to a deep corneal ulcer, although in most cases it healed uneventfully with minor changes in therapy. The use of topical prednisolone acetate during the postoperative period may also contribute to dellen formation by inhibiting corneal epithelial wound healing. However, the most important factor predisposing to dellen formation was poor tear-film integrity adjacent to the bleb. The secretion of the aqueous tears seemed to have little or no effect on dellen formation. Almost all dellen occurred in eyes with large filtering blebs.

Dellen associated with filtering blebs.

Cross-polarized photography was used to enhance the visibility of the arcuate bundles of the retinal nerve fiber layer ( NFL ) A fundus camera (Zeiss) was modified to accept a linear polarizing filter in front of the flash and another polarizing filter in front of the film plane The azimuths of the two filters were kept at right angles to one another Cross-polarized photographs were taken of the NFL of seven normal eyes and 18 eyes with ocular hypertension The polarizers were rotated together to obtain four different orientations, equally spaced through 90 degrees The manner in which visibility of the arcuate fibers was enhanced varied consistently with the orientation of the polarizing filters Cross-polarization accentuated apparent defects in the NFL when compared with standard red-free illumination

Harry A. Quigley

Papers

The contribution of glycosaminoglycans to the mechanical behaviour of the posterior human sclera.

Depth-Dependent Changes in Collagen Organization in the Human Peripapillary Sclera

The Ocusert pilocarpine system: advantages and disadvantages

Dellen associated with filtering blebs.

Cross-polarization photography of the nerve fiber layer