Primary Open Angle Glaucoma (POAG)

• Primary Open Angle Glaucoma (POAG) is the main topic

General Definition

• Chronic, progressive, bilateral, and asymmetric optic nerve damage with visual function loss characterize Glaucoma
• This occurs with an open angle
• Glaucoma happens slowly over time, gradually killing your nerves
• Elevated IOP can be related to glaucoma but doesn't have to be
• Pathological decreased IOP may be associated or be the cause, with or without elevated IOP
• Changed biomechanics in the eye might make sensitivity to IOP to optic nerve head and RNFL mechanical damage more likely
• Apoptosis of ganglion cells can lead to glaucoma progression

General Epidemiological Facts

• Glaucoma leads to blindness
• Blindness from glacoma is not recoverable
• Glaucoma is preventable with early detection and proper treatment
• Glaucoma can be difficult to diagnose
• Undiagnosed glaucoma cases are 50% in reported cases
• 50% of glaucoma diagnoses may be incorrect, leading to over-diagnosis
• Over-referrals are more effective than under-referrals

Prevalence

• Everyone, from babies to senior citizens, faces glaucoma risks
• Approximately 52.7 million people globally had POAG in 2024
• That number is projected to rise to around 80 million by 2040
• The risk is higher in older individuals, but babies can also have glaucoma, about 1 in every 10,000 births in the US
• Risk is minimal in younger people but still present

Increased Risk factors (Preferred Practice Pattern AAO 2024)

• Elevated IOP is an increased risk factor for glaucoma
• Diabetes(T2DM) relative risk
• Obstructive Sleep apnea
• Being male
• Older age
• Sibling with glaucoma
• African race or Latino race
• Myopia
• Low systolic and diastolic pressure may result in increased risk
• Disc hemorrhage
• Large cup-to-disc ratio can cause increased risk
• High pattern standard deviation on threshold visual field testing
• Thin central cornea
• Low ocular perfusion pressure is a risk factor
• Sustained hypotension can increase risk
• Thyroid disease

Classification of POAG as a Primary Open Angle

• It's the most common form of glaucoma with a normal, unblocked anterior chamber angle
• There is no identifiable anatomical event that led to decreased aqueous outflow and high IOP
• Resistance to outflow identified, but not just where
• Glaucomatous optic neuropathy develops without any underlying cause
• Bilateral presentation is common, but it tends to be asymmetric you should check the CD asymmetry
• Juvenile open angle glaucoma (JOAG) is a subtype of primary open-angle glaucoma
• JOAG is a rare subtype that occurs in individuals from 3 to 40 years of age
• Myocillin gene mutation association has one altered gene that is sufficient to have the disease

IOP

• Glaucoma can happen regardless of the intraocular pressure
• Threshold IOP for glacoma is not evidence based, relative risk increases with IOP increase
• In POAG the IOP is greater than 21
• Up to 50% of individuals with POAG present at an IOP of less than 22 mm Hg, so a diurnal measurement is needed
• IOP remains the single most important and treatable risk factor for glaucoma progression and vision loss
• IOP is a risk factor
• There are fluctuations, so a low point might be measured that day
• Only measure you can treat

Specific characteristics that define Primary Open Angle Glaucoma

• Resistance to aqueous outflow leading to elevated IOP
• Open angles
• Optic nerve head cupping
• Nerve fiber layer damage
• CCT, CH
• Visual field defects
• Other factors include: race, refractive error, vasculo-spastic Dz

Trabecular Outflow Resistance

• TM cytoskeleton
• TM endothelial cells
• Schlemm's canal
• Episcleral veins
• Normal pressure is 7-14 mmHg (10)
• Increases 1 to 9 mmHg by changing body position from seated to supine
• This increases IOP directly
• A change of 0.8 mmHg here corresponds to a change in IOP of 1 mmHg (1 to 1 roughly)
• Venous congestion
  • Thyroid orbitopathy
  • Superior vena cava syndrome

Uveoscleral Outflow Resistance

• Resistance most likely occurs within the muscular portion of the ciliary body
• Collagen between the muscle fibers resists the outflow

Elevated IOP

• Between 40 to 50% present with an initial IOP of less than 21mm Hg
• Between 1/3 and 1/2 of glaucoma patients will have an initial IOP greater than 21 mm Hg
• There is no clear IOP cut off which can be considered safe
• Some have damage at 18, others without damage at 30
• IOP is a very important risk factor and it can be regulated/treated
• Normal diurnal variation is around 5mm Hg
• Chances of optic new head damage increases as fluctuation increases
• Glaucoma patients present with more than 6-10mm Hg fluctuations
• Elevated IOP can still be treated even if there is no indication of glaucoma

Factors that Influence Elevated IOP

• Elevated episcleral venous pressure may give a false elevated reading
• Valsalva, breath holding, and tight collars can elevate IOP so patients need to be relaxed
• Supine position
• Orbital venous obstruction
• Pressure on the eye
• Blepharospasm
• Squeezing
• Thyroid Disease
• Drugs can unrelated conditions can raise IOP Topiramate, LSD, Corticosteroids, Anticholinergics, Anti-seizures

Open Angles

• Open angles are defined by gonioscopy
• Absence of synechia or other angle abnormality
• Gonioscopy always needs to be performed
• A patient needs to have an open angle for it to be POAG
• Closed angle - don't perform gonioscopy

Optic Nerve Head (ONH) Cupping

• NFL damage is the first clue, which may lead to cupping
• Structural assessment, view photo, and OCT are used with functional evaluation to monitor change over time
• Pattern of damage needs to match visual field loss

Assessing Optic Nerve Head with the 5Rs

• Use the scleral ring to determine the size of the optic nerve head, look for presence of peripapillary atrophy
• Identify the width of the neuroretinal rim
  • The space from the inside of the nerve to the beginning of the nerve can be used for counting
• Examine the retinal nerve fiber layer
• Review the region of parapapillary atrophy
• Look for retinal and disc hemorrhages
• Some other details and rules to evaluate the optic disc include:
  • Small vs. large
  • Look at the neuroretinal rim
  • Larger ones are more compressed
• This may lead to more disc damage

Classifying Optic Disc Size

• Micro: < 1.4mm2
• Average: 1.5-2.4mm2
• Macro: > 2.5mm2
• Concerning > 1.4 mm2
• Shallow cupping is less concerning, central is not of concern
• Intact lamina vs deep cupping with lamina displacement
• Large cupping of the optic nerve is significant

Cup-to-Disc Ratio (C/D) Assessment

• C/D asymmetry and vessel deflection can assess the blood vessels of the eye
• NRR tissue, pink coloration dues to axons and capillaries
• In glaucoma, the rim is pink because it's vascularized
• A pale rim indicates a compressional lesion, vascular accident, or neurological event

ISNT Rule

• Neural retinal rim follows inferior, superior, nasal, and temporal measurements
• Notching occurs at 12 and 6 o'clock and are the weakest points
• Assess for terminal glaucoma

Pallor

• Cupping occurs when pallor is glaucoma
• Isolate pallor to see cupping, exceeding neurological evaluation
• Look for pallor cupping with glaucoma and nutritional amblyopia

Other Assessments

• Displacement, vessels will move toward the natal side, that is indicative of glaucoma
• Baring of is when the vessels appear to lift off the surface of the optic nerve
• Look for zones of PPA where it affects the neurological retina

Nerve Fiber Layer (NFL) Defects

• Slit: small, thin defect along NFL
• Wedge: bigger than slip
• Diffuse issues NFL Defects Precedes field loss 5 years prior to field loss by up to 50%, NFL loss is 85% specific for glaucoma, goes to nerve NFL Technique: use red free filter to see

Other Nerve Fiber Layer Defects

• Red free is bringing out fibers
• Fibers at the papilla are thicker

Disc Hemorrhages

• At NFL level is often related to big fluctuations of IOP
• If perfusion pressure of veins cannot handle IOP they will bleed

Corneal Hysteresis (CH)

• Defined as corneal viscoelasticity due to combined effects of flexibility and rigidity
• CH reflects viscoelastic properties and overall ocular structural resistance
• Higher CH means higher corneal resistance
• Lower CH correlates with more advanced forms of POAG and more visual field loos
• CH correlates better with glaucoma than central corneal thickness

Central Corneal Thickness (CCT)

• Tend to have thinner cornea with increase of CH
• The thickness of the CCT varies is with ethnic background
• Hispanic: 546, African American: 534, Caucasian American 556, Asian: 552, Native American: 555
• CCT is Protective
• In patients with IOP greater than 26 risk is 36% if CCT 555um or less- and if 6 %: is glaucoma if CCT is 588 UM or more
• You shouldn't change glaucoma diagnoses based only on the corneal measurement
• In patients with c/d between 0.3 and 0.5-26% -with glaucoma, CCT 555um or less-4%, 588
• pachymetry is may not be an independent DX criteria
• Data implies low CCT is risk factor for glaucoma progression

Threshold Testing

• Important to see the visual fields over time
• A single test isn't enough to make a diagnosis

Humphrey's Automated Visual Field

• Autoperimetry 24-2 24 is used for a certain amount of degrees tested
• C has multiple tests
• Each test is a small variation - 54 point - Baseline- full field strategy to get results to base future tests on

Threshold Visual Field

• A single reliable test that may be used is central 30 to 2 threshold test
• This test tests 76 points -has stimulus 4 dcb above expected value at central and peripheral points -records midpoint stimulus (the part until no longer peceived)

Visual Field Defects Respect Horizontal Meridian

• Test Asymmetry because each the progression is never vertical
• most initial is Para central
  • Isolate depressions within 20 degrees of -joining scotomas
  • Bjerrum as arcuate

Progression and Nerve Fibers

• Needs to check asymmetrical because there is nasal step to check that it is with the nerve

Visual field defect -isnt Rule

• There is W-W perimetry ,short wave perimetry can deteck that early

Frequency Double Technologies

• Good for quick screening
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