6.1.8. Evaluates glaucoma risk factors to detect glaucoma and refer accordingly.

Question 1

Risk Factors for POAG

Answer 1

• 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

Question 2

Signs posing a Risk

Answer 2

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)

Question 3

Visual fields:

Answer 3

• reproducible visual field test defect consistent with optic disc appearance
• relative or absolute arcuate scotoma, nasal step, paracentral loss

Question 4

Applanation tonometry:

Answer 4

• 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

Question 5

Risk factors for NTG

Answer 5

Age

Female

Vascular disease

Japanese

FH

Question 6

Risk Factors for PCAG

Answer 6

• 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

Question 7

Signs posing a Risk

Answer 7

• 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

Question 8

Risks of developing COAG from OHT?

Answer 8

• 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!!

Question 9

What is the criteria, urgency & pathway for referral?

Answer 9

• 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
• Potentially occludable angle as judged by van Herick test (this guidance is subject to change, please follow UPDATED college guidelines!)
  
  • NICE does not provide guidance on referral for angle closure; however SIGN recommends that patients with peripheral anterior chamber width of ≤25% of the corneal thickness (van Herick Grade 1 or 2) should be referred to secondary eyecare services (this guidance may have changed!)

Question 10

PAC Suspect

Answer 10

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

Question 11

PAC

Answer 11

Refer urgently within a week if IOP 30mmHg or higher with occludable angles

Question 12

What measurements should be taken for suspect COAG?

Answer 12

IOPs - preferrably Goldmann

CCT measurement

Visual field assessment - central threshold & repeated if necessary - can be full or suprathreshold

Optic nerve head assessment - preferably with dilation, stereoscopic

Anterior chamber assessment - nasal & temporal preferably or even gonioscopy (gonioscopy will be done at HES & referral refinement as routine unless contraindicated)

Stereoscopic image of ONH or Disc maps using OCT

Question 13

Glaucoma Risk Factors POAG

Answer 13

• 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
  *

Question 14

Glaucoma Risk Factors NTG

Answer 14

• 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
  *

Question 15

Glaucoma Risk Factors PACG

Answer 15

• 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
  *

Question 16

Secondary glaucoma’s

Answer 16

Pseudoexfoliation (open angle)
* PXF = grey-white fibrillary amyloid-material
* Symptoms worsen following exercise

Pigment dispersion (open angle)
* Young, white, myopic males
* Pigment is deposited on corneal endothelium Krukenberg spindle

• Hyphaemia (open angle)
• Blood in AC caused by trauma

Phacomorphic (closed angle)
* Lens size increases and blocks drainage

Rubeosis iridis may lead to neovascular glaucoma
* Pxs with ischaemic CRVO / DR are at risk of developing this
* Iris forms membrane onto TM and new vessels grow within the angle

Question 17

Primary open angle glaucoma

Answer 17

• Open drainage angle
• Occurs in the absence of any other ocular, systemic or pharmacological cause and accompanied by IOP >21mmHg
• 2 proposed mechanisms by which raised IOP is thought to cause glaucomatous damage
• Vascular dysfunction - results in ischaemia to optic nerve
• Mechanical dysfunction/ trabecular dysfunction - trabecular meshwork gradually becomes less effective allowing aqueous to pass through to Schlemm’s canal (increased outflow resistance)

Question 18

Normal tension glaucoma

Answer 18

• Glaucoma without evident secondary cause which follows a chronic time course and occurs in the presence of an open anterior chamber angle
• OAG where IOP has rarely been recorded above 21mmHg
• Proposed mechanisms
• Higher sensitivity to normal pressure
• Vascular dysregulation
• Abnormally high translaminar pressure gradient
• A neurodegenerative process due to impaired cerebrospinal fluid dynamics in the optic nerve sheath compartment
  *

Question 19

Angle closure glaucoma

Answer 19

•  Group of conditions that result in closure of the anterior chamber angle, ultimately resulting in glaucoma
•  Different mechanisms which can cause angle closure
  o Pupil block - failure of aqueous flow through pupil leads to a pressure difference between anterior and posterior chambers, resulting in anterior bowing of the iris
  o Non-pupillary block - important in many far eastern patients, associated with a deeper AC than pure pupil block

Question 20

Chronic angle closure

Answer 20

• The iris slowly comes into contact with an increasing area of trabecular meshwork, resulting in TM dysfunction and a gradual rise in IOP
• Gradual and/or spiking of IOP causing optic disc damage that looks like that of OAG
• Open but narrow angle or shallow AC / ITC on gonioscopy – irido trabecular contact – if the iris touches the trabecular meshwork
• Hypermetropia – above 2/3D

Question 21

Intermittent angle closure

Answer 21

• The angle is narrow but open, but certain physiological states (producing dilation) lead to transient rises in IOP which resolve over variable periods of time
• This often produces transient symptoms of acute angle closure
• Intermittent brow ache, haloes

Question 22

Acute angle closure

Answer 22

• • Dilation of pupil leads to angle closure
• • Marked rise in IOP due to: pupil block (pupil builds up behind iris and pushes it forwards) or peripheral iris tissue occluding the angle - often present at the same time.
• • Blurred vision/haloes
• • Brow ache/headache
• • Nausea
• • Red eye
• • Fixed mid-dilated pupil
• • Hazy blue/green cornea – caused by the way the light is reflected/refractive when the cornea is oedematous
• • Iritis
• • IOP > 40mmHg
• • Shallow AC
    *

Question 23

Glaucomatous disc features

Answer 23

1. C:D ratio
2. Blood vessel position
3. Rim thickness
4. Pallor
5. Peri-papillary atrophy
6. APON (acquired pit of ON)
7. Haemorrhage
8. Nerve fibre layer defects
9. Notches – like APONs, highly focal loss of tissue
10. Laminar dots
11. Nasalisation of BVs

Question 24

Cup to disc ratio

Answer 24

Measure disc size first

 Since the ONH has a direct bearing on degree of cupping, it is essential to estimate the overall disc diameter
 The best method to do so is using the beam of a slit lamp
 Multiplication factors
o 60D – 1.0
o 78D – 1.1
o 90D – 1.4
o Superfield – 1.5

 Small disc – less than 1.5mm
 Medium disc – 1.5-2.0mm
 Large disc - greater than 2.00

 Important to measure vertically
 Superior and inferior aspects contain the most neural tissue and therefore are where changes are most likely to be identified first
 Interpret results alongside disc size
 NICE indicate that a 0.2 difference is clinically significant

Question 25

Assess width of NRR

Answer 25

* Narrowest rim/disc ratio should be recorded & considered alongside additional indicators of glaucoma * In general, ON is positioned slightly superiorly to the horizontal raphe, as a result the inferior aspect has the greatest concentration of ganglion cell axons * In most discs, this translates that inferior is where the NRR is broadest * (DDLs) *

Question 26

PPA

Answer 26

* 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 * It is found adjacent to the ONH *

Question 27

Focal NRR loss

Answer 27

 Occurs in a localised area of tissue, usually at the poles of the disc  More common in NTG

Question 28

Diffuse NRR loss

Answer 28

 Occurs when ganglion cells are lost in a more uniform manor  More common in POAG

Question 29

Disc haemorrhages

Answer 29

 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

Question 30

Bayonetting of blood vessels

Answer 30

 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

Question 31

Baring blood vessels

Answer 31

 i.e., flyover vessels  baring occurs with enlargement of the cup  The rim narrows and leaves the vessels isolated/bared

Question 32

Laminar dots/changes in laminar cribrosa

Answer 32

 Laminar cribosa becomes more visible  Pores in laminar cribrosa become more visible, enlargement of pores indicate RNFL loss

Question 33

Disc pallor

Answer 33

 Disc pallor is more likely to be another optic neuropathy  Ensure you check for: altitudinal VF defect / RAPD

Question 34

RNFL loss

Answer 34

 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

Question 35

IOP

Answer 35

 Mean 15.5 mmHg  Standard deviation 2.5mmHg  Normal range 10-21mmHg  IOP should be similar between eyes  Approx. 33% of glaucoma patient have NTG with IOP <21mmHg  Majority of eyes with IOP over 21mmHg = no detectable signs of glaucoma = OHT  Higher mean IOP in black ethnicity (18.7mmHg) o Also have thinner corneas; potential for tonometry errors and decreased tolerance to raised IOP  Lower mean in people of Asian ethnicity; especially east Asian (13mmHg)  Family history o Higher IOP with FHx of OHT or glaucoma

Question 36

Pachymetry & CCT

Answer 36

 Pachymetry = measurement of CCT  Normal = 555 microns  Range 480 to 600 microns  Corneal thickness = thicker in periphery  Variations o Diurnal = thicker in the morning (oedema) o Disease = thicker in Fuch’s o Age = CCT decreased with age in Asian people o Ethnicity = black people have corneas that are 17-60microns thinner than white  Thinner cornea = less force to applanate = under estimation  Thicker cornea = more force to applanate = over estimation  Eyes with thinner corneas have: o 3 times increase risk of glaucoma o Earlier VF loss and more advanced disease at diagnosis

Question 37

Visual fields

Answer 37

 If a defect is present, needs to be described and decided if it’s likely to be glaucomatous  Glaucoma is typically bilateral, but asymmetrical – VF loss reflects this  The vertical and horizontal asymmetry of the visual loss is also characteristic of glaucoma

Question 38

Paracentral

Answer 38

 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

Question 39

Arcuate

Answer 39

 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

Question 40

Nasal step

Answer 40

 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

Question 41

Overall depression

Answer 41

 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

Question 42

Glaucoma (SIGN GUIDELINES) for routine referral

Answer 42

 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

Question 43

Topical hypotensive

Answer 43

1. Prostaglandin analogue e.g. Latanoprost (Xalatan)  Increase uveoscleral outflow by ciliary muscle relaxation  30-35% IOP reduction  Main ADRs: iris hyperpigmentation & eyelash changes 2. Beta-blocker e.g. timolol,  Decrease aqueous production  25-30% IOP reduction  Increase risk of systemic side effects e.g. systemic hypotension, exacerbation of asthma, heart failure o Do not give to asthmatics/COPD/heart issues o Do not give px already on beta-blocker for hbp; this will already have a IOP lowering effect, if still high then topical beta-blocker may not have much of an effect as it works in the same mechanism 3. Carbonic anhydrase inhibitor e.g. brizonolamide (azopt)  Decrease aqueous production  18% IOP reduction 4. Alpha 2 agonist e.g. brimonidine tartrate (alphagan)  Decrease production & increase outflow  25% IOP reduction

Question 44

PACG drugs

Answer 44

 Pilocarpine (cholinergic agonist) qds o Increases trabecular outflow o Side effect of long-term use = severe headaches  Systemic acetazolamide (carbonic anhydrase inhibitor) o Reduces aqueous production  YAG iridotomy if narrow/closed angles

Question 45

Other options for treating glaucoma:

Answer 45

 Selective laser trabeculoplasty – likely 1st choice if hypotensives don’t work  MIGS – minimally invasive glaucoma surgery i.e. iStent o Bypass the trabecular meshwork to drain aqueous  Trabeculectomy – surgical procedure  Ahmed vale