6.1.8. Evaluates glaucoma risk factors to detect glaucoma and refer accordingly. Flashcards
Risk Factors for POAG
- Thinner central cornea - pachymetry
- The risk is greater in eyes with OHT & CCT <555µm & lower in eyes with high CCT (>588µm)
- Remember that a thin cornea underestimates the IOP & so gives an artefactually lower reading than it should
- Narrow angles - Van herick
- FH (25% if 1 parent)
- Age 40+
- Myopia > 3D
- Hypertension
- Cardiovascular & cerebrovascular condition
- Race - West african decent including west indians & Afro-Caribbean (3-4x more likely) - age 40+, (Afro-caribbeans, Asians then Caucasian)
- Diabetes? (controversial) - probably don’t mention it
- UV?
- POAG or NIAON in fellow eye
- Gender M=F
Signs posing a Risk
Optic disc:
- Generalised thinning, focal narrowing or notching of neuroretinal rim. ISNT rule NOT obeyed
- Cupping should be considered in relation to disc size. Deep cup with small disc is not a good sign.
- Deep cup with lamina cribrosa prominent (soft sign)
- CD ratio >0.6 or R:L asymmetry ≥ 0.2 suspicious of glaucoma. Vertical cup size > Horizontal
- PPA - alpha (darker, more on the outside) or beta (lighter, more on the inside)
- Disc margin haemorrhage is an important prognostic sign but not necessarily diagnostic of glaucoma (more common in Normal Tension Glaucoma). Must rule out secondary causes such as diabetes
- Bayoneting of the optic nerve head vessels (soft sign)
- Defects of the nerve fibre layer visible in younger patients
- If available, establish baseline using stereo-photography or with computer-based image analysis e.g. confocal scanning laser ophthalmoscope (CSLO) or ocular coherence tomography (OCT)
Visual fields: sign
- reproducible visual field test defect consistent with optic disc appearance
- relative or absolute arcuate scotoma, nasal step, paracentral loss
Applanation tonometry:
- IOP >21mmHg
- greater central corneal thickness produces artefactually high IOP measurements
- lesser central corneal thickness produces artefactually low IOP measurements
NB: in a significant proportion of patients with glaucoma, IOP is in normal range (Normal Tension Glaucoma) - greater than normal diurnal variation in IOP (>4 mm Hg)
- measure IOP at different times of day; usually highest in morning
- difference of 4-5mmHg between eyes is suspicious
Van Hericks:
- Should be grade 3 or 4
Risk factors for NTG
Age
Female
Vascular disease
Japanese
FH
Risk Factors for PCAG
- FH
- Increasing Age 40-50 years, (AC becomes shallower as lens thickness increases)
- Women (3:1)
- Chinese & south asians
- High hyperopia
- Short axial length
- Small corneal diameter
- Drug induced:
- Adrenergic agents e.g. phenylephrine
- Drugs with anticholinergic effects e.g. tricyclic antidepressants
- Drugs that may cause ciliary body oedema, e.g. topiramate, sulphonamides
- Surgery Induced:
- Angle closure may follow a number of surgical procedures, for example vitreo-retinal surgery with intraocular gas, especially in aphakic eyes
Signs posing a Risk
- In a PAC suspect the eye may appear normal (with the exception of a narrow angle, as judged by the van Herick technique or by gonioscopy).
- Van hericks of 1 to 2,
- Elevated IOPs >21 suspect
Risks of developing COAG from OHT?
- Age (per decade)
- Mean IOP (per mmHg)
- Central corneal thickness (per 40μm thinner)
- Pattern standard deviation (per 0.2dB greater)
- Vertical cup-to-disc ratio (per 0.1 larger).
- REMEMBER:
- THINNER CORNEA MEANS IOP UNDERESTIMATED! THIS MEANS THAT WHILST THE INITIAL READING IS LOW, THE ACTUAL READING COULD BE HIGHER IF CCT CORRECTED
- ERROR OF 5mmHg POSSIBLE!!
What is the criteria, urgency & pathway for referral?
- IOP >21mmHg ONLY IF with other signs indicative of glaucoma e.g. field loss, assymetrical discs etc.
- IOP 5mmHg or greater difference between the eyes
- Ocular hypertension - high IOP without signs of glaucoma or secondary cause
- Refer only if IOP is 24mmHg or more using Goldmann-type applanation tonometry. Advise people with IOP below 24 mmHg to continue regular visits to their primary eye care professional
- Around 10% of ocular hypertensives will develop glaucoma in 5 years
- Refer for further investigation and diagnosis of COAG and related conditions, after considering repeat measures as in recommendation 1.1.4, if:
- there is optic nerve head damage on stereoscopic slit lamp biomicroscopy or
- there is a visual field defect consistent with glaucoma or
- IOP is 24mmHg or more using Goldmann-type applanation tonometry
PAC Suspect
Can only be diagnosed by gonioscopy. The decision to refer for further treatment should be based on the risk of developing PAC/PACG or AAC. If not referring for further investigation, patients with PACS require close monitoring and serial gonioscopy. Patients should be aware that they are at risk of occlusion and that certain medications could induce angle closure
Normal Ranges of IOP
- This is the main risk factor for developing glaucoma (not enough drainage or too much aqeuous)
- Mean IOP in population is 15.5mmHg
- Distribution is not perfectly normal, slight positive skew towards higher IOPs
Normal distribution would predict 2.5% above 21mmHg- In fact, 5% have IOPs above 21mmHg - classed as OHT if with open filtration angles & no detectable glaucomatous damage
- The upper range of normal in those above 70 years old is 23mmHg
POAG risks
- Race – 4x more common in individuals of African descent
- Myopia >4D
- Large optic disc
- Thin cornea
- Diabetes
- High blood pressure
- Peripheral vascular disease
- Contraceptive pill
- Ocular hypertension – 10% over 5 years / asymmetry >4mmHg
*
NTG risks
- Ethnicity – Japanese 4-12x more likely
- Myopia >4D
- Raynaud’s Phenomenon
- Migraine
- CCT tends to be lower than in POAG
- Gender – females
- Systemic hypotension
- Myopia
- Thyroid disease
*
PACG risks
- Race – far eastern and Indian Asians
- Refraction – hypermetropic
- Short axial length – narrow AC
- Age >40 – AC becomes narrow as lens becomes thicker
- Gender – females
- Family history – genetic factors are important but poorly defined
Secondary glaucoma’s
Pseudoexfoliation Glaucoma (Open Angle)
- Cause: Deposition of grey-white fibrillary amyloid material (PXF).
- Symptoms: Worsen following exercise.
Pigment Dispersion Syndrome (Open Angle)
- Predisposition: Young, white, myopic males.
- Signs: Pigment deposition on corneal endothelium forming Krukenberg spindles.
Hyphaemia-Associated Glaucoma (Open Angle)
- Cause: Blood in the anterior chamber (AC) due to trauma.
Phacomorphic Glaucoma (Closed Angle)
- Cause: Enlargement of the lens, leading to blockage of aqueous drainage.
Neovascular Glaucoma
- Cause: Rubeosis iridis with new vessel formation in the angle.
- Risk Factors: Ischaemic CRVO or Diabetic Retinopathy (DR).
- Mechanism: Formation of fibrovascular membrane on the trabecular meshwork (TM).
PPA
More prevalent in areas with NRR damage
Alpha zone PPA (black arrows) = areas of increasing irregular RPE pigmentation. This is supposed to occur first, and as there is an increasing RPE loss, so it develops into beta zone PPA
Beta zone PPA (blue arrows) = areas of partial or complete loss of RPE and some choriocapillaris, with visibility of larger choroidal vessels becoming more apparent
o It is found adjacent to the ONH
Focal NRR loss
Occurs in a localised area of tissue, usually at the poles of the disc
More common in NTG
Diffuse NRR loss
Occurs when ganglion cells are lost in a more uniform manor
More common in POAG
Disc haemorrhages
Often first sign of a problem
All/some of haemorrhage contained within optic disc
More common in NTG
Blood cells in the superficial layers of the ONH will be flame/feather shaped
More subtle haemorrhages occur when blood is released into deeper layers before axons go through the 90-degree bend; appear as faint dot haemorrhages
Bayonetting of blood vessels
When thinning of the NRR reaches the disc margin, a sharpened rim is produced
If a retinal vessel crossing sharped rim, it will bend sharply at the end of the disc
Baring blood vessels
i.e., flyover vessels
baring occurs with enlargement of the cup
The rim narrows and leaves the vessels isolated/bared
Laminar dots/changes in laminar cribrosa
Laminar cribosa becomes more visible
Pores in laminar cribrosa become more visible, enlargement of pores indicate RNFL loss
Disc pallor
Disc pallor is more likely to be another optic neuropathy
Ensure you check for: altitudinal VF defect / RAPD
RNFL loss
RNFL defects represent the drop out of anterior bundle of ganglion cell axons
Nerve fibre bundle defects are often the repeat of repeated disc haemorrhages
They are best seen with red-free light and clear media, and appear as dark wedge shape originating from the disc margin against the lighter striations of the NFL
For large defects, localised notching of the NRR is often seen where the defect meets the disc margin
Pachymetry & CCT
Pachymetry and Central Corneal Thickness (CCT)
Normal Values
- Average CCT: 555 microns
- Normal Range: 480 to 600 microns
- Corneal thickness increases in the periphery.
Variations in CCT
- Diurnal: Thicker in the morning due to corneal oedema.
- Disease: Thicker in Fuch’s dystrophy.
- Age: Decreases with age in Asian populations.
- Ethnicity:
- Black individuals have corneas 17–60 microns thinner than white individuals.
Effect on IOP Measurement
- Thinner Cornea:
- Requires less force to applanate → Underestimation of IOP.
- Risk: 3x higher chance of glaucoma; earlier VF loss and more advanced disease at diagnosis.
- Thicker Cornea:
- Requires more force to applanate → Overestimation of IOP.
Paracentral
Usually in the superior VF initially; may be relative or absolute
Scotoma may be single or multiple and can increase in number / join to form arcuate defects
Paracentral defects are thought to occur more commonly in cases of low / NTG
Arcuate
Due to localised partial or complete damage to a nerve fibre layer bundle and scotoma follows the shape of this bundle
Gives rise to characteristic defect, which can be absolute, relative or combination of both
As the disease progresses, these arcuate defects may extend in an arcuate shape from the upper and lower poles of the blood spot
They can then widen into the peripherally and centrally, eventually leaving the patient with only a central island of vision
Nasal step
Nasal step describes the most remote end of an arcuate defect
Vertical discontinuity across the raphe in the temporal retina gives sharply delineated step in the nasal field plot when comparing superior and inferior hemifields
Overall depression
An overall depression can also be a soft sign of glaucoma caused by global RNFL damage
There are many other causes for an overall depression; therefore it is only a soft sign
Glaucoma (SIGN GUIDELINES) for routine referral
Optic disc signs consistent with glaucoma
Reproduceable VF defect in either eye
Risk of angle closure (VG G1 / gonio > 270deg TM not visible)
OHT IOP >25mmHg, irrespective of CCT
OHT - IOP <26mmHg and CCT <555
o OHT meaning IOP >21mmHg
Emergency / same day for IOP >40mmHg / red eye / angle closure
Topical hypotensive
Glaucoma Medications
1. Prostaglandin Analogues (e.g., Latanoprost - Xalatan)
- Mechanism: Increases uveoscleral outflow by relaxing ciliary muscles.
- IOP Reduction: 30–35%.
- ADRs:
- Iris hyperpigmentation.
- Eyelash changes (lengthening, darkening, thickening).
2. Beta-Blockers (e.g., Timolol)
- Mechanism: Decreases aqueous humor production.
- IOP Reduction: 25–30%.
- ADRs:
- Systemic hypotension.
- Exacerbation of asthma or COPD.
- Risk of heart failure.
- Contraindications:
- Asthma, COPD, or cardiovascular issues.
- Patients already on systemic beta-blockers (e.g., for hypertension), as topical beta-blockers may have reduced efficacy.
3. Carbonic Anhydrase Inhibitors (e.g., Brinzolamide - Azopt)
- Mechanism: Reduces aqueous humor production.
- IOP Reduction: ~18%.
4. Alpha-2 Agonists (e.g., Brimonidine Tartrate - Alphagan)
- Mechanism:
- Decreases aqueous humor production.
- Increases uveoscleral outflow.
- IOP Reduction: ~25%.
Other options: Glaucoma Treatment Options (Surgical and Laser)
1. Selective Laser Trabeculoplasty (SLT)
- Often the first choice if hypotensive medications fail.
- Targets the trabecular meshwork to enhance aqueous drainage.
2. MIGS (Minimally Invasive Glaucoma Surgery)
- Examples: iStent, Hydrus Microstent.
- Mechanism:
- Bypasses the trabecular meshwork to improve aqueous outflow.
- Less invasive than traditional surgeries, shorter recovery time.
3. Trabeculectomy
- Surgical procedure to create a new drainage pathway for aqueous humor.
- Often used in advanced or refractory glaucoma.
4. Ahmed Valve Implant
- A tube shunt device that helps drain aqueous humor to an external reservoir.
- Typically used in severe or complex glaucoma cases.
