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Glaucoma
Published in Charles Theisler, Adjuvant Medical Care, 2023
Glaucoma is a group of eye conditions that damage the optic nerve, leading to loss of vision or blindness. Glaucoma develops often as a result of abnormally high pressure in the anterior chamber of the eye. However, not every person with increased eye pressure will develop optic nerve damage.1 There are two major types of glaucoma: open angle and closed angle. Open angle is the most common form, accounting for 90% of all cases. At first, open-angle glaucoma has no symptoms. It causes no pain and vision stays normal. Nonetheless, over time and without treatment, increased intraocular pressure damages the optic nerve. In closed-angle glaucoma, drainage canals are blocked so pressure in the eye increases. Individuals with glaucoma gradually lose their peripheral (side) vision. If glaucoma remains untreated, objects to the side and out of the corner of the eye can be missed. In more advanced cases, patients often report that their vision is like looking through a tunnel. Over time, central vision may also decrease until no vision remains.1
Principles and Methods of Ocular Pharmacokinetic Evaluation
Published in David W. Hobson, Dermal and Ocular Toxicology, 2020
Once in the anterior chamber, the drug must traverse this 3 mm deep, liquid-filled space through which the fluid is passing at 1% of the total volume per minute. Since the volume is about 250 μl, the flow rate is roughly 2 to 2.5 μl/min. This fluid is formed at the ciliary processes and passes into the anterior chamber through the pupil. If the pupil is relatively small, i.e., 3 to 4 mm, then the velocity of the fluid passing between the anterior lens surface and the posterior face of the iris is fairly high. If it has overcome these impediments to diffusion, then the compound must pass either through or around the lens, and into the gel-like vitreous in order to reach the posterior pole of the eye. The characteristics of the vitreous humor, however, change with age, causing the vitreous to become more liquid.2 Thus, the penetration characteristics of this bulk compartment also may change with aging of the eye.
The Special Sense Organs and Their Disorders
Published in Walter F. Stanaszek, Mary J. Stanaszek, Robert J. Holt, Steven Strauss, Understanding Medical Terms, 2020
Walter F. Stanaszek, Mary J. Stanaszek, Robert J. Holt, Steven Strauss
Other diseases can also impair vision. Glaucoma is characterized by an increase in intraocular pressure (IOP). Most cases of primary glaucoma are of the open-angle type (primary open-angle glaucoma or POAG), where IOP may fluctuate but the aqueous humor outflow is consistently decreased. Angle-closure or narrow-angle glaucoma occurs when the anterior chamber angle is blocked by the root of the iris, causing severe pain and loss of vision along with the increase in IOP. Complications include cataracts, atrophy (tissue wasting) of the retina and optic nerve, and blindness (amaurosis, typhlosis).
Design and Methodology of a Multi-Centre Clinical Trial of Low Dose Laser Cycloplasty for the Treatment of Malignant Glaucoma in China
Published in Ophthalmic Epidemiology, 2022
Haishuang Lin, Jibing Wang, Sujie Fan, Zuohong Wu, Xiaoping Xu, Qinhua Cai, Lijun Zhao, Sumian Cheng, Shaodan Zhang, Yuanbo Liang
An evaluation of the safety of the procedures was conducted and covered: Corneal injury: corneal injury was sought via an examination by conducting a corneal endothelium cell count.Anterior uveitis: inflammation in the anterior chamber was indicative of anterior uveitis.Hyphema: hyphema was determined by slit lamp examination.Lens injury: lens injury was determined following an examination by slit lamp.Hypotony: an IOP of ≤5 mmHg was defined to be hypotony.
Analyzing Anatomical Factors Contributing to Angle Closure Based on Anterior Segment Optical Coherence Tomography Imaging
Published in Current Eye Research, 2022
Bingsong Wang, Kai Cao, Zhiheng Wang, Ye Zhang, Nathan Congdon, Tao Wang
The current study showed that smaller posterior corneal curvature (PCC) is one of the parameters most strongly associated with angle closure. Friedman and colleagues showed that the contralateral eyes of individuals with acute angle closure had steeper radii of corneal curvature compared with eyes of population-based control subjects.30 Congdon and colleagues sought to identify ocular biometric parameters to explain the excess burden of angle closure among Chinese and found that radius of corneal curvature was significantly smaller among Chinese than whites or blacks.5 The cornea covers the anterior surface of the anterior chamber and connects with the peripheral iris to form the angle. Previous studies showed that anterior chamber width (ACW) was independently associated with narrow angles.23 Our analysis showed different result. Although ACW was significant in univariate analysis, it showed collinearity and was excluded in Lasso regression analysis. PCC, ACW and CD were in the same subgroup and were closely related to one other. However, only PCC had an independent effect on angle closure. Smaller cornea curvature deserves more attention as an independent anatomical characteristic for angle closure in future studies.
Topical drug delivery to the retina: obstacles and routes to success
Published in Expert Opinion on Drug Delivery, 2022
The space between the cornea and the iris, the anterior chamber, contains a clear aqueous liquid called aqueous humor [64]. It has relatively low viscosity and its chemical composition resembles that of blood plasma although it has lower protein content (and less drug protein binding). Its total volume in humans is between 200 and 300 μl. It is continuously secreted by the ciliary body and then drained by the trabecular meshwork and the uveoscleral pathway. The rate of aqueous humor turnover follows a circadian rhythm and varies between 1.5 (at night) and 3.0 µl/min (in the morning) [65]. The vitreous humor (about 4 ml) consists of mainly (99%) of water in a network of collagen and hyaluronic acid [66]. It is a rather firm hydrogel that helps to keep the retina in place and maintain the spherical shape of the eye. Dissolved drug molecules permeate the vitreous via an aqueous pathway between the collagen and hyaluronic acid mesh. After intravitreal injection, hydrophilic and high-molecular-weight drugs (e.g. proteins and peptides) are removed from the vitreous humor via the anterior route to the aqueous humor, while small lipophilic drugs that easily pass the retina are removed via the posterior route with the choroidal blood flow [34]. The half-life of a dissolved drug in the vitreous humor is typically less than 10 to 24 hours, where small molecules have shorter half-life than larger ones like proteins [8,67]. Consequently, intravitreal drug delivery systems most frequently consist of polymeric particles and inserts that can release controlled amounts of drugs for several weeks or even months.