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.

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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.

Current and future approaches to glaucoma screening.

This study was undertaken to identify features of optic nerve head architecture that might explain, in part, why ganglion cell loss occurs in patients with low-tension glaucoma. We compared retrospectively the disc photographs of 25 patients with low-tension glaucoma with those of 26 control patients with typical open-angle glaucoma. No differences were observed in any of the following features: pore length, shape, or size variation; cup/disc and disc/arteriole ratio; clock positions of total rim loss; central retinal vessel entry site; rim pallor; number of rim-crossing vessels; and presence or absence of peripapillary nerve fiber layer hemorrhages, optic pits, and central retinal vessel canals. An hour-glass appearance of connective tissue bundles within the scleral lamina cribrosa, however, was present statistically less often in patients with low-tension glaucoma (p = 0.007). We speculate that the microscopic arrangement of fiber bundles within the lamina cribrosa may play an etiologic role in the pathogenesis of low-tension glaucoma.

Comparison of optic disc features in low-tension and typical open-angle glaucoma.

Purpose There has been recent interest in the potential use of gene therapy techniques to treat ocular disease. In this article, we consider the optic nerve diseases that are potentially most amenable to gene therapy. Methods We discuss the recent success of gene transfer experiments in animal models of glaucoma, optic neuritis, Leber's hereditary optic neuropathy (LHON), and optic nerve transection, and we assess the possibility of using similar techniques to treat human disease in the future. Results We have achieved highly efficient transfection of retinal ganglion cells in a rat model of glaucoma following a single intravitreal injection of adeno-associated virus (AAV). In our model, we have found that AAV-mediated gene therapy with brain-derived neurotrophic factor has a significant neuroprotective effect compared to saline or control virus injections. Guy and co-workers have successfully used AAV-mediated gene therapy to replace the defective mitochondrial enzyme subunit in cells derived from human patients with LHON. Gene therapy techniques have also shown promise in animal models of optic neuritis and optic nerve trauma. Conclusions Human diseases with single-gene defects such as LHON may soon be treated successfully by gene therapy, assuming that vectors continue to improve and are well tolerated in the human eye. Other optic nerve diseases such as glaucoma that do not have a single-gene defect may also benefit from gene therapy to enhance RGC survival. In all cases, the risks of treatment will need to be balanced against the potential benefits.

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Gene therapy for optic nerve disease

The presence and distribution of laminin, heparan sulfate proteoglycan and collagen types I, III and IV were immunohistologically determined in cynomolgus monkey optic nerve heads using the avidin-biotin-peroxidase complex technique. Collagen types I and III were detected within the collagenous plates of the scleral lamina cribrosa, in the septa and pia mater of the postlaminar optic nerve and in blood vessel walls in all regions of the optic nerve head. Collagen type IV, laminin and heparan sulfate proteoglycans were all localized to the margins of the collagenous laminar plates of the scleral lamina cribrosa and along the margins of the optic nerve septa and the pia mater. All three components also appeared beneath the blood vessel endothelium throughout the optic nerve head. Within the lamina cribrosa, collagen types I and III occupy the core of the scleral laminar plates and may provide structural support for optic nerve bundles exiting the eye. The distribution of collagen type IV, laminin and heparan sulfate proteoglycan corresponds to basement membranes from two sources: vascular endothelial cells and glial cells lining the axonal bundles. Abnormalities of these substances may influence optic nerve function and susceptibility to elevated intraocular pressure by altering their mechanical support functions within the nerve head, by interfering with axonal nutrition, or both.

The extracellular matrix composition of the monkey optic nerve head.

BACKGROUND Limited data are published on the ultrasound biomicroscope (UBM) findings of the anterior chamber angle. This work provides a population-based assessment of angle findings and compares 3 modalities for assessing angle dimensions. METHODS A sample of 268 persons who had participated in a population-based study of glaucoma prevalence in Singapore were reexamined by UBM (nasal, temporal, and inferior angles only), Scheimpflug photography of angle width, and gonioscopy. Angle findings were compared, and age and sex influences evaluated. RESULTS The temporal angle was the widest of the 3 angles imaged with the UBM, and the inferior angle was the narrowest (nearly 20% more narrow than the temporal angle, P<0.005). Women were found to have narrower angles than men and older persons had more narrow angles. Scheimpflug photography did not provide enough detail of the angle to increase our understanding of angle anatomy. CONCLUSIONS The data reported support earlier findings that the anterior chamber angle is narrower in older individuals and women. Methods of assessing the angle may themselves influence the appearance of the angle. Limited agreement exists between the angle quantification methods studied. An ideal method of angle assessment would not contact the eye and would not require light be directed at the eye.

Age and sex variation in angle findings among normal Chinese subjects: a comparison of UBM, Scheimpflug, and gonioscopic assessment of the anterior chamber angle.

Harry A. Quigley

Papers

Current and future approaches to glaucoma screening.

Comparison of optic disc features in low-tension and typical open-angle glaucoma.

Gene therapy for optic nerve disease

The extracellular matrix composition of the monkey optic nerve head.

Age and sex variation in angle findings among normal Chinese subjects: a comparison of UBM, Scheimpflug, and gonioscopic assessment of the anterior chamber angle.