Glaucoma I

A group of optic neuropathies characterized by retinal ganglion cell (RGC) death that results in excavation of the optic disc and visual field loss, with or without elevated IOP.

Neuronal death and glaucoma progression can continue even with very effective IOP lowering. Many new treatments for glaucoma attempt to prevent retinal ganglion cell death through the concept of neuroprotection.

• Intraocular pressure (IOP)
• Age (>40 yrs)
• Race/ethnicity (blacks)
• Family history
• Myopia (nearsightedness)
• Thin central cornea thickness

Second most common cause of blindness.

Most common cause of irreversible blindness.

Primary Open Angle Glaucoma (POAG) is the most common form of glaucomas.

Typically bilateral, may be asymmetric.

The prevalence of POAG increases with increasing age.

Blacks have an increased risk. POAG in blacks is typically more severe and occurs at an earlier age.

No sex predilection in POAG.

Primary Angle Closure Glaucoma (PACG): Less frequent than POAG in the black. More common than POAG in the Eskimo Chinese population.

In the normal eye, aqueous humor produced by the ciliary body epithelium is released into the posterior chamber and flows into the anterior chamber and exits the eye through the trabecular meshwork (TMW) or uveoscleral pathways.

1. Increased intraocular pressure
2. Interference with axoplasmic flow at the lamina cribrosa
3. Deprivation of trophic factors
4. Release of glutamate into the extracellular space and vitreous
5. Ischemia (induced by elevated IOP or as a primary insult)
6. Immune-mediated nerve damage
7. Oxidative stress

• Etiology: primary or secondary
• Pathogenic mechanism: open angle or closed angle
• Age of onset: childhood or adult

Primary glaucomas: Result from developmental, degenerative abnormalities, hereditary factors that affect the channels of aqueous outflow.

Secondary glaucomas: Result from a large variety of injuries, toxic medications, systemic disorders, or ocular diseases that primarily damage other ocular tissues and only secondarily affect the outflow channels.

The terms open angle and closed angle refer to the anatomical configuration of the anterior chamber angle. The classification is made by gonioscopy.

In open-angle glaucoma, the chamber angle has its normal configuration; aqueous humor bathes the surface of the trabecular meshwork (TMW). Primary open-angle glaucoma occurs in the absence of other ocular disease or congenital anomalies.

In closed-angle glaucoma, the root of the iris lies against the trabecular meshwork.

Angle closure may be partial or complete, intermittent or constant, reversible or permanent.

AGE OF ONSET

Childhood glaucomas

In congenital glaucoma, a developmental malformation of the anterior chamber angle causes glaucomatous damage to the optic nerve head.

Classification of Childhood Glaucoma

A. Primary congenital or infantile glaucoma:

Congenital glaucoma, when present at birth.

Infantile glaucoma, if it appears during the first year of life.

Juvenile-onset glaucoma, if it arises later during the first 2 decades of life.

The cause, in most varieties, is a malformation of the trabecular meshwork (TMW).

B. Secondary glaucomas in children

1. Secondary to or associated with other ocular abnormalities:
• Axenfeld's anomaly
• Rieger's syndrome
• Peters' anomaly
2. Secondary to systemic diseases:
• Sturge-Weber syndrome
• Neurofibromatosis
• Marfan's syndrome
• Homocystinuria

ADULT ONSET GLAUCOMAS

PRIMARY GLAUCOMAS

• Primary open-angle
• Ocular hypertension
• Low / Normal tension
• Primary closed-angle
• Acute
• Intermittent
• Chronic

SECONDARY Glaucomas

• Exfoliative
• Pigmentary
• Steroid-induced
• Iritis
• Trauma
• Lens-induced
• Aphakic glaucoma
• Secondary to tumor
• Neovascular
• Ghost cell
• Raised episcleral venous pressure
• Topical or systemic corticosteroid use
• Syndromes (e.g., Axenfeld-Rieger syndrome)
• Angle closure (buckling, scleritis, laser)

Normal tension glaucoma (NTG) or (LTG)

A subtype of primary open-angle glaucoma where the IOP constantly remains within the statistically determined normal range, but progressive optic neuropathy and visual defects typical of glaucoma occur. It requires repeated tonometry, including 24-hour phasing (24-hour IOP assessment).

Ocular Hypertension:

IOP is consistently higher than statistically normal, but optic disc and visual fields are normal.

Slit lamp examination of the anterior segment

This is a detailed examination of the front portion of the eye using a specialized microscope with a bright light. It allows for a close inspection of the cornea, iris, lens, and other anterior eye structures.

Tonometry

Tonometry is a procedure used to measure intraocular pressure (IOP) in the eye. Elevated IOP is a risk factor for glaucoma, so this test helps in glaucoma diagnosis and management.

Fundoscopy

Fundoscopy, also known as ophthalmoscopy, is an examination of the back of the eye, including the optic nerve, retina, and blood vessels. It is performed using an ophthalmoscope, which allows visualization of the retina's condition.

Gonioscopy

Gonioscopy is a diagnostic procedure that evaluates the drainage angle of the eye, specifically the angle between the iris and the cornea. It is essential in determining the type and risk of glaucoma.

Visual Fields

Visual fields testing assesses a person's peripheral vision. It is crucial in detecting visual field defects, which can occur in glaucoma and other eye conditions.

Pachymetry

Pachymetry measures the thickness of the cornea, the clear front surface of the eye. Corneal thickness is a factor in assessing the risk of glaucoma.

Optical Coherence Tomography (OCT)

OCT is an imaging technique that uses light waves to create cross-sectional images of the eye's structures. It provides detailed information about the layers of the retina and is valuable in glaucoma management and other eye conditions.

Intraocular Pressure (IOP): Intraocular pressure refers to the pressure inside the eye. It is typically measured in millimeters of mercury (mm Hg). The normal range for IOP is usually maintained between 10 to 21 mm Hg in healthy eyes.

Mean IOP: Mean IOP represents the average intraocular pressure in a given population or group. In a healthy population, the mean IOP is often around 16 mm Hg.

Normal IOP: In a healthy individual, normal IOP can vary throughout the day due to circadian variation. The range of normal IOP in a person's eye can be between 4 to 6 mm Hg, with IOP typically being highest in the early morning.

Tonometry is the process of measuring intraocular pressure (IOP) within the eye. It is a critical component of assessing eye health.

Tonometry can be performed using two main methods:

1. Indentation Tonometry: This method involves the use of instruments like the Schiotz tonometer. It measures IOP by assessing the amount of indentation or deformation of the cornea when a fixed amount of force is applied. The accuracy of this old method may depend on other ocular factors such as scleral rigidity.
2. Applanation Tonometry: Applanation tonometry is performed using instruments like the Goldmann or Perkins tonometers. This method applies a variable amount of force to flatten the corneal surface. It is considered more precise and is commonly used in clinical settings.

Tonometry

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Tonometry

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Tonometers

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Tonometers

Gonioscopy

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Gonioscopy: Viewing the AC angle

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Gonioscopy: Viewing the AC angle

Grading the Anterior Chamber (AC) Angle:

From the iris root and proceeding anteriorly towards the peripheral cornea, structures in an open angle are:

1. Iris Root: This is the starting point and represents the base of the iris, the colored part of the eye.
2. Ciliary Body Band (G:IV): The ciliary body is a ring-shaped structure located behind the iris. It plays a vital role in producing aqueous humor. A Grade IV ciliary body band suggests a healthy angle configuration.
3. Scleral Spur (G:III): The scleral spur is a ridge-like structure at the junction of the iris and the cornea. It helps support the iris and maintain the angle's shape. A Grade III scleral spur indicates proper angle anatomy.
4. Trabecular Meshwork (G:II): The trabecular meshwork is a sieve-like tissue located in the angle. It is responsible for draining aqueous humor from the eye. A Grade II trabecular meshwork signifies normal drainage function.
5. Schwalbe's Line (G:I) (SL): Schwalbe's Line is the innermost part of the cornea's Descemet's membrane. It forms the boundary of the drainage angle. A Grade I Schwalbe's Line (SL) is the most anterior and indicates a wide, open angle.
6. Peripheral Cornea (G:0): The peripheral cornea is the clear front part of the eye that joins with the white sclera. A Grade 0 peripheral cornea suggests a wide and open anterior chamber angle, which is ideal for proper aqueous humor drainage and eye health.

In the case of Iris-cornea touch, the angle is generally graded as G III and IV, indicating it is open. However, when the angle is narrow and occludable/closable, it is graded as G I.

Grading

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Grading

Several grading systems- Shaffer's, Spaeth's, Scheie's

Gonioscopic grading of Angle closure [Shaffer's]

Grade	Angle width	Configuration	Chances of closure	Structures visible
IV	35°-45°	Wide open	Nil	SL,TM,SS,CBB
III	20°-35°	Open angle	Nil	SL,TM,SS
II	20°	Moderately open	Possible	SL,TM
I	10°	Very narrow	Highly likely	SL only
0	0°	Closed	Closed	None

Ophthalmoscopy (Fundoscopy)

Clinical evaluation of the optic nerve head.

• Direct ophthalmoscopy provides a highly magnified erect view through an undilated pupil.
• The normal optic nerve head or "disk" is vertically oval in shape. The neural retinal tissue of the optic nerve has a pinkish-orange appearance.
• The central cup is vertically oval in shape, similar to, but smaller in size than the overall optic nerve.
• The normal C:D Ratio (Cup-to-Disk Ratio) may vary from 0.2 to 0.5.

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Clinical evaluation of the optic nerve head.

• Direct ophthalmoscopy provides a highly magnified erect view through an undilated pupil.
• The normal optic nerve head or "disk" is vertically oval in shape. The neural retinal tissue of the optic nerve has a pinkish-orange appearance.
• The central cup is vertically oval in shape, similar to, but smaller in size than the overall optic nerve.
• The normal C:D Ratio (Cup-to-Disk Ratio) may vary from 0.2 to 0.5.

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Perimetry

Perimetry: Assessment of the Visual Field (VF)

VF is a portion of space visible to the fixating eye at a given time.

Static and Kinetic Perimetry:

• Static perimetry: It uses a stationary light stimulus of variable intensity which may be increased until the subject recognizes the stimulus. The stimulus may be presented at various points in the visual field.
• Kinetic perimetry: It uses a moving stimulus of fixed intensity, moved at a steady rate from outside the visual field into the seeing area, at which point it is perceived by the patient.

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The anatomy of the retinal nerve fiber layer as it enters the optic nerve accounts for the patterns of the visual field defects seen in glaucoma.

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The anatomy of the retinal nerve fiber layer as it enters the optic nerve accounts for the patterns of the visual field defects seen in glaucoma.

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The major patterns of visual field loss characteristic of glaucoma are:

1. (a) Diffuse decrease in sensitivity, primarily peripherally;
2. (b) An arcuate scotoma involving the area about 15 degrees from fixation; and
3. (c) A dense paracentral scotoma that starts nasal to fixation.

Nerve fiber bundle loss results in the most definitive and reproducible visual field defects seen in early glaucoma. Nerve fiber bundle defects include:

• Arcuate or Bjerrum defects
• Nasal step defects
• Temporal wedge defects
• Paracentral scotomas

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Central Corneal Thickness - CCT

Some patients diagnosed with Ocular Hypertension (OHT) may be normotensive when corrected for increased corneal thickness.

Some supposed glaucoma suspects or patients with apparent low-tension glaucoma (with normal range IOPs on applanation) can have abnormally thin corneas on pachymetry (central corneal thickness measurements); therefore, their IOP measurements are underestimated by applanation.

OCT: Optical Coherence Tomography

Linear scan through the optic disc. A linear tomogram through the optic disc provides cross-sectional information for assessing disc and cup parameters.

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