10 - normal tension glaucoma

What is the definition of normal tension glaucoma?

AAO: form of open-angle glaucoma characterized by glaucomatous optic neuropathy in patients with IOP measurements consistently lower than 21 mmHg

Glaucoma Foundation: condition characterized by progressive optic nerve damage and VF loss with a statistically normal IOP

What is NTG considered a part of?

POAG spectrum

What % of glaucoma cases are NTG?

25-30% → large proportion of glaucoma patients

What are the 3 general distinctions of NTG from POAG?

1. non-IOP related pathophysiology

2. unique presentation

3. treatment considerations

What are the suspected pathophysiologies of NTG?

1. reduced OPP (ocular perfusion pressure)

2. large translaminar pressure difference (ICP vs IOP)

why does reduced OPP causes NTG?

reduced ocular blood flow may serve as hypoxic stimulus for glaucomatous neuropathy → anything that diminishes diastolic BP below certain levels can be harmful to ONH perfusion

What are the accepted risk factors for NTG?

1. nocturnal hypotension

2. sleep apnea

3. vasospastic disease → migraine, Raynauds phenomenon

4. hemodynamic crisis

5. primary vascular dysfunction (PVD)

What are the suspected risk factors for NTG?

1. carotid artery disease

2. high cholesterol

3. hypercoagulation disorder

4. severe anemia

5. cardiac arrhythmia

6. blood dyscrasias

What is the translaminar pressure difference equal to?

TPD = IOP - intracranial pressure

How do people with NTG TPD compare to control's?

NTG has a higher TPD (even though they have the same IOP as the control group) → therefore lower ICP

How does transluminar pressure difference affect NRR area?

increased TPD → lower NRR

What is the common variable in OPP and TPD that affects NTG?

IOP

What are the clinical characteristics of NTG?

1. saucer-like cupping with temporal rim thinning (or global)

2. deep but localized visual field loss often near fixation

3. drance heme

what type of glaucoma are drance hemes more common in?

NTG

What is saucerization?

ill defined shallow cup

What is saucerization associated with?

overall decrease in visual field sensitivity

what glaucoma is saucerization more common in?

NTG

Why does NTG often have paracentral defects?

NTG often has temporal rim thinning → causing VF defects near fixation/central

what does a genetically weak lamina cribosa put RGC axons at risk for?

RGC axons within the macular vulnerability zone are susceptible to mechanical damage from relatively low IOP

Who should you do a GCA on?

ALL glaucoma patients → including NTG

what does GCA thinning correspond to?

paracentral VF defects

What is the best VF method to quantify paracentral defects?

10-2

how many degrees is 10-2 separated by?

separated by 2 degrees from 10 degrees away from fixation

What are the risk factors for presenting with a paracentral glaucomatous defect?

1. migraine

2. low blood pressure

3. sleep apnea

4. drance heme

What does a drance heme represent?

nerve under stress

Does a drance heme occur before or after axon damage?

unsure! can be either

What is one of the most significant predictors of glaucoma progression?

drance heme

What is the initial trigger of concern for NTG?

ONH appearance

how do differentiate between physiological cupping and damage by glaucoma?

1. large discs have large cups

2. physiological cupping is consistent over time, glaucoma progresses

3. physiological cupping is not usually associated with functional vision loss, glaucoma is

What are the differential diagnoses for NTG?

1. red's disease

2. physiological cupping

3. POAG with masked high IOP

4. intermittent angle closure

5. secondary glaucoma

6. non-glaucomatous optic neuropathy

What can mask high IOP in POAG making you think NTG?

1. thin CCT (<545)

2. treatment with systemic beta blocker

3. diurnal IOP measurement

How can you see if it is NTG or intermittent angle closure causing the glaucomatous defects?

1. gonioscopy

2. post-dilation IOP

How big of an IOP spike post-dilation indicates a closed angle component?

>4mmHg → may benefit from cataract sx or LPI

what secondary glaucomas can appear as NTG?

1. pseudoexfoliative glaucoma

2. pigment dispersion syndrome

3. previous uveitic glaucoma

what non-glaucomatous optic neuropathies can appear as NTG?

1. ischemic, compressive or prior traumatic optic neuropathy

2. optic neuritis

what are the characteristics of non-glaucomatous neuropathy?

1. unilateral

2. pallor > cupping

3. decreased VA

4. dyschromatopsia

5. VF loss respecting the vertical midline

6. VF damage worse than disc appearance

7. rapidly progressing VF or VA loss

What tests are helpful in detecting NTG?

1. 10-2

2. GCA

3. fundus photos → drance heme

4. color vision → non-glaucoma

5. corneal hysteresis

What was the inclusion criteria for the collaborative NTG study?

1. average IOP ≤20

2. no history of documented IOP >24

3. open angles

4. no systemic beta blockers

5. no other apparent cause for optic neuropathy or VF loss

What were the results of the collaborative NTG study?

65% of untreated eyes did not progress

35% of untreated eyes progressed, while only 12% of treated eyes progressed

*IOP reduction is beneficial for those at risk of progression → 2/3 are NOT at risk*

What are the risk factors for progression according to the collaborative NTG study (i.e. needs treatment)?

1. disc heme

2. migraine

3. female

african ancestry (maybe)

What were the confirmed NON risk factors for progression according to the collaborative NTG study?

1. baseline IOP

2. age

3. FHx

4. hypertension

How should you manage NTG?

1. do not rush to treat

2. check for progression over time

3. check IOP at different times of day

4. consider extra testing → sleep apnea, MRI

What % reception in IOP do you want when treating NTG?

30% reduction

What is often a treatment needed in NTG to reach 30% IOP reduction?

trabeculectomy

What is the first line medication in NTG?

prostaglandins

What medications are contraindicated for NTG?

avoid β-blockers due to risk of decreased OPP

brimonidine may be neuroprotective (not really because it was compared to β-blockers)

What were the results of the low tension glaucoma treatment study?

brimonidine + timolol elicit equal drops in IOP

BUT

9% of brimonidine pts progressed, while 40% of timolol patients progressed

HOWEVER

more brimonidine patients dropped out of the study, so cannot decide if brimonidine is neuroprotective or not

disregard

disregard