Encyclopedia of Glaucoma

A topical collection in Encyclopedia (ISSN 2673-8392). This collection belongs to the section "Medicine & Pharmacology".

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Collection Editor
Department of Anatomy and Cell Biology, New York Medical College, Valhalla, NY 10595, USA
Interests: ophthalmology, cell Biology; anatomy; neurology

Topical Collection Information

Dear Colleagues,

Glaucoma is the leading cause of blindness in the world. The recent meta-analysis predicts the number of patients affected with glaucoma to be around 110 million worldwide. 

Glaucoma is an optic neuropathy characterized by the selective death of retinal ganglion cells (RGCs) and a progressive loss of vision. The elevation in intraocular pressure (IOP) is one of the important risk factors for developing glaucoma. There are at least six different kinds of glaucoma:

  • Primary open angle, or chronic glaucoma. About 90% of cases fall in this category.
  • Acute angle-closure glaucoma. This type is considered the most serious and is designated as a medical emergency.
  • Normal tension glaucoma, in which IOP is normal yet RGCs continue to die.
  • Secondary glaucoma: other medical conditions, such as the formation of extra blood vessels in the area where aqueous humous drains, thereby elevating the IOP. Causes of such conditions can be diabetes or high blood pressure. Secondary glaucoma also includes:
    1. pigmentary glaucoma, where the pigment from the iris disperses and blocks the drainage pathway, thereby increasing the IOP;
    2. exfoliation glaucoma, where extra material deposits on parts of the eye, blocking the drainage pathway.
  • Congenital glaucoma: babies born with a condition have symptoms such as cloudy eyes, sensitivity to light, or larger-than-normal eyes.
  • Uveitic glaucoma involves swelling and inflammation (uveitis), which can lead to scar formation that may block the drainage pathways.

An increase in IOP can also be induced by blunt injury to the eyeball.

Treatment of glaucoma to date aims at surgically or medically reducing the elevated IOP, which has been identified by various studies as the sole critical factor for the pathogenesis of glaucoma.  Various contributions from basic sciences (biochemistry, molecular biology, cell biology, molecular genetic) have added tremendous knowledge to the glaucoma field, so much so that the mysteries of glaucoma have begun to unravel. This wealth of knowledge has propelled the field to a point that the future of effectively treating or controlling the disease seems to be nearly in reach.

The principal tenet of glaucoma is that as IOP is elevated, RGCs begin to die. RGCs are the cells in the retina whose axons send the visual information to the visual brain centers. Unfortunately, when dead, the RGCs cannot be replaced by any known method. The result is blindness.

Detailed studies of the pathogenesis of glaucoma began when animal models of glaucoma were created. The earliest model of experimentally induced glaucoma was in the monkey. Because of the cost of maintaining many monkeys, and for other ethical reasons, this line of research, which dealt with factors leading to RGCs and has been used to test many drugs, has limited use and has been mostly eliminated.

In 1995, we published the first animal glaucoma model in rats (Shareef et al. 1995), in which we could obtain chronically high IOP. This model protects the structure of trabecular meshwork, does not affect the ciliary nerve, and high IOP can be maintained for up to 6 months. The development of this model and numerous variations of this technique of cauterizing deep episcleral veins and the introduction of other models has allowed us and other scientists to conduct pharmacological trials of different combinations and concentrations to study the reduction in IOP and the elucidation of cellular and molecular mechanisms pertaining various aspect of glaucoma. The protection of RGC death has set the stage for the subsequent study in larger animals such as pigs. Using rats or mice as an experimental model allowed us to study the mechanism of RGC death following elevated IOP. Most studies in the pathogenesis of glaucoma have used this animal model.

Since the inception of animal models, hundreds of studies have been carried out that delt with detailed mechanisms of RGC death and neuroprotection of RGCs by various cell biological techniques. Due either to the use of different animal models or different methodologies, numerous controversies have arisen. For example, do RGCs die first and then their axons, or vice-versa?

The field of glaucoma studies has utilized numerous modern biological methods to answer the question of how to save RGCs from death: 

  • use of trophic factors;
  • use of stem cells to replace or assist in saving the cells;
  • gene therapies on how the brain visual centers adapt to the remaining RGCs following limited death of these cells;
  • transplant approaches to reconstruct optic pathways;
  • studies of congenital animal models of glaucoma;
  • regeneration of injured RGC axons.

The published data on glaucoma have become so large that it is deemed necessary to create an encyclopedia of scientific contributions that will enable students, post-doctoral fellows, residents, and clinicians to find out what has been accomplished and determine where further research is needed.

The methods cited above are just a few of the subtopics that will be included in the Encyclopedia of Glaucoma.

Prof. Dr. Sansar Sharma
Collection Editor

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Published Papers (3 papers)

2023

Jump to: 2022

10 pages, 260 KiB  
Entry
Intraocular Pressure during Spaceflight and Risk of Glaucomatous Damage in Prolonged Microgravity
by Mouayad Masalkhi, Joshua Ong, Ethan Waisberg, John Berdahl and Andrew G. Lee
Encyclopedia 2023, 3(4), 1187-1196; https://doi.org/10.3390/encyclopedia3040086 - 28 Sep 2023
Cited by 4 | Viewed by 1967
Definition
Microgravity introduces diverse pathological and various physiological changes to the human body, including intraocular pressure. Astronauts may develop a constellation of symptoms and signs including optic disc edema, choroidal folds, and a hyperopic shift from the flattening of the globe. These ocular findings [...] Read more.
Microgravity introduces diverse pathological and various physiological changes to the human body, including intraocular pressure. Astronauts may develop a constellation of symptoms and signs including optic disc edema, choroidal folds, and a hyperopic shift from the flattening of the globe. These ocular findings have been collectively termed spaceflight-associated neuro-ocular syndrome (SANS). SANS is a condition that is unique to long-duration spaceflight. The precise pathogenesis of SANS remains ill-defined, but several hypotheses have been proposed that may be influenced by intraocular pressure. Countermeasures for SANS research also include techniques that impact intraocular pressure. In this article, we discuss intraocular pressure during spaceflight, the translaminar pressure gradient, SANS and potential SANS countermeasures, and the potential for glaucomatous damage during spaceflight. Full article
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Graphical abstract

9 pages, 584 KiB  
Entry
Improving Compliance with Medical Treatment Using Eye Drop Aids
by Amit Biran, Mordechai Goldberg, Nadav Shemesh and Asaf Achiron
Encyclopedia 2023, 3(3), 919-927; https://doi.org/10.3390/encyclopedia3030065 - 23 Jul 2023
Cited by 1 | Viewed by 1804
Definition
Achieving optimal treatment outcomes in glaucoma requires patients to adhere to their medication regimens. Possible barriers to patients’ cooperation include the misunderstanding of a treatment’s importance or errors in applying instructions, forgetfulness, financial constraints and others. Due to the fact that glaucoma usually [...] Read more.
Achieving optimal treatment outcomes in glaucoma requires patients to adhere to their medication regimens. Possible barriers to patients’ cooperation include the misunderstanding of a treatment’s importance or errors in applying instructions, forgetfulness, financial constraints and others. Due to the fact that glaucoma usually causes no apparent symptoms or pain, on the one hand, and the significant inconvenience that the eye drops used for glaucoma treatment can cause due to local irritation, on the other, patient compliance is a challenge. To address this challenge, we require strategies for improving adherence to glaucoma treatment. The importance of proper eye drop administration techniques cannot be overstated, particularly for vulnerable populations such as the elderly, the sick and the visually handicapped. Studies have shown that failure to comply with glaucoma treatment is a significant factor affecting disease progression, emphasizing the need for interventions that improve patient compliance. Educational interventions, medication reminders and the use of assistive devices such as eye drop aids have been shown to improve adherence to glaucoma treatment. By promoting strategies that can be used to enhance treatment adherence, healthcare providers can ensure that glaucoma patients receive the full benefits of their treatment plans, reducing the risk of disease progression. Many patients struggle with the complexity of their treatment regimens and the challenges of administering eye drops. This entry provides a comprehensive overview of the different barriers to patient adherence to glaucoma eye drop treatment, emphasizing the difficulties associated with eye drop instillation. This entry examines a range of eye drop aids available to patients, evaluating their modes of action, benefits, drawbacks and effectiveness in improving patient compliance. By providing detailed information on the barriers to adherence and the range of eye drop aids available, this entry aims to support healthcare providers in helping glaucoma patients to achieve better treatment adherence and outcomes. Full article
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2022

Jump to: 2023

8 pages, 991 KiB  
Entry
Pathogenesis of Glaucoma
by Jason Macanian and Sansar C. Sharma
Encyclopedia 2022, 2(4), 1803-1810; https://doi.org/10.3390/encyclopedia2040124 - 13 Nov 2022
Cited by 2 | Viewed by 5344
Definition
Glaucoma, a neurodegenerative disease, has a varied pathogenesis scenario, including elevated intraocular pressure (IOP), and hypoxic conditions in the retina. Consequently, degenerating optic axons at the optic nerve head are observed clinically when extensive damage has already occurred. Following elevated IOP, changes in [...] Read more.
Glaucoma, a neurodegenerative disease, has a varied pathogenesis scenario, including elevated intraocular pressure (IOP), and hypoxic conditions in the retina. Consequently, degenerating optic axons at the optic nerve head are observed clinically when extensive damage has already occurred. Following elevated IOP, changes in retinal ganglion cells lead to apoptosis immediately followed by degeneration of their optic axons. Degradation of axons leads to cupping of the optic nerve head and visual field losses. Here we emphasize that it is the retinal ganglion cells that are initial targets of elevated IOP, and, together with hyperactivity of retinal astrocytes, create the ischemic conditions which represent the earliest sign in the pathogenesis of glaucoma. Full article
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