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Glaucoma and the Optic Nerve Naida Jakirlic, OD, FAAO Western University of Health Sciences College of Optometry September 13, 2015
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Learning objectives
• Review the anatomy of the optic nerve
• Recognize the appearance of the healthy optic nerve
• Ascertain the critical components of optic nerve assessment
• Identify possible glaucomatous changes of the optic nerve,
peripapillary region, and RNFL
• Identify the cardinal features of glaucomatous optic neuropathy
• Analyze optic nerve images to solidify today’s discussion
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What is glaucoma?
A progressive optic nerve disease characterized by
retinal ganglion cell death and resultant axon loss seen
as excavation of the optic nerve head with consequent
defects in retinal sensitivity that can be measured with
visual field tests
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What is glaucoma?
• Optic neuropathy
• Axon loss
• Excavation of the optic nerve
• Resultant VF defects
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Glaucomatous damage may be due to
• Elevated IOP
• Poor perfusion pressure to the ONH
• Obstruction of axoplasmic flow within the ganglion cell axons
• Anatomic weakening of the lamina cribrosa
▫ Myopia
▫ Optic nerve pits
• Programmed cell death of the ganglion cell axons (apoptosis)
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Pre-perimetric glaucoma?
20-40% of ganglion cells are lost before VF defects
are detected on standard automated perimetry
So what?
Assessment of the ONH is critical for early
diagnosis and management to prevent VF defects
before they occur
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Optic Nerve Head (ONH) • Careful evaluation of the ONH has high specificity and good
precision for glaucoma diagnosis
• It is one of the most important aspects of glaucoma assessment
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Anatomy of the optic nerve • Ganglion cell axons make up 90% of
neuroretinal rim tissue of the optic disc
▫ 1-1.5 million axons leave via the ONH through the scleral canal
▫ Grouped into bundles by glial cells
• Remainder of neuroretinal rim is composed of capillaries and astrocytes
• Axons in superior and inferior poles have less structural support
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Anatomy of the ONH
• Four distinct layers of the ONH
▫ Surface layer
▫ Prelaminar ONH
▫ Laminar ONH
▫ Retrolaminar ONH
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Anatomy of the ONH • Surface layer
▫ Anterior limit of the ONH
▫ Point of contact with the vitreous
▫ Peripheral edge is defined by anterior limits of the scleral ring
▫ Posterior limit: axonal bundles have completed 90 degree turn from the plane of the retina and reached the level of the choroid
Surface ONH
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Anatomy of the ONH
• Prelaminar ONH
▫ Indistinct segment of axons surrounded by outer retina, choriocapillaris,
and choroid
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Anatomy of the ONH
• Laminar ONH
▫ Ganglion cell axon bundles wrapped in glial cells and confined in rigid
pores of the lamina cribrosa
Laminar ONH
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Anatomy of the ONH
• Retrolaminar ONH
▫ Posterior to lamina cribrosa
▫ ONH thickness is doubled by presence of myelinating oligodendrocytes
Retrolaminar ONH
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RNFL distribution
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Lamina cribrosa • Composed of several sheets of connective tissue
▫ Fenestrated to allow passage of nerve fiber bundles carrying
ganglion cell axons
• Variable number of pores: 200-600
▫ Larger pores at superior and inferior poles - may provide less
support than smaller fenestrations in nasal and temporal regions,
resulting in greater damage to RGC axons in these areas
• Laminar dots become more exposed and numerous with progressive
axon loss
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Lamina Cribrosa
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Changes in the lamina cribrosa
• Normally pores are obscured by nerve fibers
• As nerve fibers undergo atrophy, pores become more visible
▫ AKA laminar dot sign
▫ Can be present in healthy eyes
• Thinning and backward bowing of lamina cribrosa occurs with
deepening of cup
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Thinning and backward bowing of LC
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Laminar dot sign
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ONH Blood supply
• Superficial ONH ▫ Branches from CRA
• Pre-laminar ONH ▫ Short posterior ciliary
arteries (SPCA) • Laminar ONH ▫ Circle of Zinn-Haller:
anastomoses of adjacent SCPA’s
• Retro-laminar ONH ▫ SPCA ▫ Pial vascular plexus ▫ Axial vasculature from CRA
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Ocular perfusion pressure
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Venous drainage
• Via central retinal vein
• In chronic glaucoma, shunt vessels
may appear due to disturbed retinal
circulation
▫ AKA optociliary shunt vessels
▫ Pre-existing capillaries that become
more visible as they dilate to re-route
blood around an area of obstruction
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Optociliary shunt vessels • Differential diangoses ▫ CRVO ▫ Optic nerve sheath meningioma ▫ Chronic glaucoma ▫ Chronic papilledema
• Different from neovascularization of the disc ▫ Do not leak on FA
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Optic cup
• Central excavation in the ONH
• Devoid of axons and capillaries
▫ Pale due to visibility of collagenous lamina cribrosa
▫ Size is dependent on number of nerve fibers leaving the eye
and the size of the scleral canal
• Cup depth usually depends on cup size
▫ Small cup = shallow
▫ Large cup = deep
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Optic cup • High inter-individual variability
• Lies below the level of the neural rim
• Bottom is formed by the LC
• Border between cup and rim is determined by contour, not the color
▫ Point of deviation of vessels on the surface of the ONH
▫ Area of pallor of the cup usually corresponds to the borders of the cup
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Contour vs. color
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Contour < color
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Contour = color
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Contour vs. color
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Optic cup variants
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Optic cup variants
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Optic cup variants
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Changes in the optic cup
• Increased size
• Increased depth
• Visualization/increase in laminar dots
• Vertical enlargement
▫ Localized neuroretinal rim loss at superior and inferior poles
• Asymmetry between two eyes greater than 0.2
▫ In the absence of disc size asymmetry
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Optic pit • Localized weakening in the lamina cribrosa • Usually located infero-temporally • More prevalent in NTG • Will have a corresponding but stable VF defect
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Neuroretinal rim
• Point of exit of nerve fiber bundles
from the eye through the scleral
canal
• Healthy rim tissue should be pink
due to presence of pre-laminar
capillaries
• May be difficult to assess in high
myopes, patients with tilted discs,
and nerves with significant pallor
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Peripapillary area • Elschnig’s scleral ring ▫ Thin white ring outside of disc margin ▫ AKA scleral lip ▫ Anterior extension of sclera between the
choroid and the optic nerve – RPE and choroid stop short of the disc
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Peripapillary area • Choroidal crescent
▫ RPE stops short of the disc
▫ Underlying choroid visible
▫ Usually slate-gray in color
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Peripapillary area • Peripapillary RPE hypertrophy
▫ Darker than choroidal crescent
▫ Increased amount of peripapillary RPE pigment
▫ Normal variant
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Peripapillary area • Grey crescent: located within scleral lip on the neuroretinal rim
▫ Caution: may lead to false interpretation of neuroretinal rim – may be interpreted as thinner than it truly is
▫ May be pigmentation within the neural tissue cells – melanocytes, RPE cells, or free pigment granules
▫ Normal finding
vs.
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Peripapillary area • Zone alpha ▫ Found in normals
• Zone beta ▫ More common in glaucoma patients
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Peripapillary zones
• 1 = cup • 2 = neuroretinal rim • 3 = scleral crescent • 4 = zone beta • 5 = zone alpha
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Optic nerve variants
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Optic nerve variants
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Caution: myopic nerves
• Certain features of highly myopic discs interfere with interpretation
of the neuroretinal rim and amount of cupping
▫ Large disc area
▫ Oblique insertion of optic disc causing distorted view of the
temporal rim
▫ Tilt makes assessment of superior and inferior poles difficult
▫ Shallow cupping makes C/D ratio difficult to assess
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Caution: myopic nerves & oblique insertion
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Caution: myopic nerves • Wide temporal peripapillary crescent causes difficulty in assessing
temporal rim • In this case, look at asymmetry and the integrity of the nasal rim
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Myopic nerves: pearls and pitfalls
• Photodocumentation is vital to evaluate for change
▫ Serial imaging with OCT to monitor for change is extremely beneficial
▫ Caution: normative databases on imaging technologies do not apply
• Any change in VF status is suspicious
• May have higher risk of converting into glaucoma due to weakened
lamina cribrosa
• May be more vulnerable to even slight IOP increase due to longer
globe, thinner LC, and thinner scleral wall
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Optic disc evaluation in glaucoma
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Goals of optic disc evaluation
Diagnose: distinguish between normal and abnormal
Quantify: how much damage has occurred 20-40% of ganglion cell axons can be lost before reproducible VF
loss appears on automated perimetry Ganglion cells die at the level of the lamina cribrosa, with
retrograde atrophy back to their cell bodies in the retina
Monitor for change
Stable
Worsening
Quantify rate of change: slow vs. rapid
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Optic disc evaluation Slit lamp biomicroscopy: ideal Stereoscopic view Measuring optic disc size
Direct ophthalmoscopy Good magnification No stereo
Indirect ophthalmoscopy Poor magnification and detail
Optic disc photography Great for documentation and monitoring for progression Always taken at baseline, and usually every 2 years afterwards
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What to look for? Disc: size and shape
Neuroretinal rim: size, shape, color, localized defects (notching)
Cup: size and shape in relation to the optic disc size
0.7 C/D in a 1.8mm nerve – probably NOT ok
0.7 C/D in a 2.7mm nerve – probable NOT glaucoma
Optic disc hemorrhage: presence and location
Nerve fiber layer defect
Peripapillary atrophy
Retinal arterial attenuation
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Optic disc size
Critical in distinguishing between physiologic and pathologic
cupping
• Scleral foramen/canal: 1-3mm
▫ Large foramen = large disc = large cup
▫ Small foramen = small disc = small cup
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Optic disc size
Measurement of vertical disc diameter
Length of vertical beam of slit lamp light
Multiplied by correction factor of condensing lens
Volk 60D: x 1.0
Volk 78D: x 1.1
Vold 90D: x 1.3
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Optic disc size • Average vertical diameter: 1.8-2.0mm
• Small optic nerve vertical diameter: <1.5 mm
• Large optic nerve vertical diameter: >2.2mm
2.7 mm
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Disc vs. cup size • Larger discs = larger cups ▫ Due to the size of the scleral canal
• Always determine the size of the disc
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Large disc = large cup
3mm
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Small disc = small cup
1.5 mm
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Early and moderate glaucomatous
damage in small discs may be
missed due to initial low C/D ratios
3mm 1.5 mm
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C/D ratio
Optic disc elongation
Vertically oval optic disc
Horizontally oval optic cup
In normal eyes: horizontal C/D ratio > vertical C/D ratio
In glaucomatous eyes: vertical C/D ratio > horizontal C/D ratio
Documentation
Always include horizontal and vertical CD ratio
Stereophotographs of the ONH always beneficial
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Neuroretinal rim
• Reflects selective loss of tissue
• It is the primary location of pathologic changes
• C/D ratio is often a poor indicator of early glaucoma
• Pay attention to the width and the health of the neuroretinal rim
• Look at the donut, not at the hole!
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The neuroretinal rim
Size
Shape
The ISNT rule
Color
Glaucoma: cupping WITHOUT pallor
I>S>N>T
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The ISNT rule
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The ISNT rule
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The neuroretinal rim
Look for
Thinning
Notching: localized defect in the neuroretinal rim
Pallor: suspect a different or additional optic neuropathy
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The neuroretinal rim
Usual sequence of loss in glaucoma:
Inferotemporal/superotemporal
Temporal
Inferonasal/superonasal
In non-glaucomatous optic nerve damage, the rim is not always
affected, therefore its contour is maintained
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Patterns of cupping • Diffuse cupping
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Patterns of cupping • Focal atrophy: notching
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Patterns of cupping • Bean-pot cupping ▫ Extreme posterior displacement of lamina cribrosa
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Peripapillary chorioretinal atrophy
Irregular pigmentation around the optic nerve
Nonspecific finding
Seen in normals
Should raise suspicion for POAG and NTG
Associated with acquired damage to the optic nerves from glaucoma
Clinical appearance
Moth-eaten appearance of the RPE temporal to ONH
Adjacent to area of neuroretinal rim thinning
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Peripapillary atropy
• Zone Alpha ▫ Hypo and hyper pigmented areas
due to RPE irregularity ▫ Nasally bounded by zone beta ▫ Temporally bounded by normal
retina ▫ Present in normal eyes ▫ Present in glaucomatous eyes
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Peripapillary atropy • Zone Beta ▫ Atrophy of the RPE and
choriocapillaris ▫ May be due to poor perfusion to the
peripapillary area ▫ Large choroidal vessels become
visible ▫ More common in glaucomatous
eyes
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Peripapillary atrophy Helps differentiate between glaucomatous and non-glaucomatous
optic nerve damage Beta zone larger and more frequent in glaucoma Nasal PPA more frequent in glaucoma
• Width of beta zone inversely correlated with adjacent rim width ▫ Larger beta zone thinner neuroretinal rim
• Progression of beta zone associated with progression of glaucoma
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Zone β Zone α
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Vascular changes • Optic disc hemorrhages
• Baring of curcumlinear vessel
• Bayonetting of vessels
▫ Advanced cupping causes vessels to emerge from floor of the cup, disappear as they ascend up the excavated wall of the cup, and emerge again at the disc margin
• Nasalization of vessels: major vessels show nasal shift
• Optic nerve shunts/collaterals
• Retinal artery attenuation
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Optic disc hemorrhage Aka drance hemorrhage Splinter or flame shaped Located on the disc margin Hallmark of glaucomatous optic nerve damage 4-10% of eyes with glaucoma
Found in early and moderate stages, rare in advance stages Usually located on IT and ST disc margins
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Optic disc hemorrhage Can resolve within 6-10 weeks of onset Can take anywhere between 2-35 weeks
Associated with localized RNFL defects and rim notching Suggests progression Appearance may precede RNFL loss, notching, and VF
defect More common in NTG Can be seen in PVD, BRVO, HTN retinopathy, and NAION
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Baring of vessels
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Bayonetting of vessels
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Nasalization of vessels
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Optic nerve shunts/collaterals
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Retinal artery attenuation
Diffuse narrowing
Decreasing neuroretinal rim
Increased RNFL loss
Infreased VF defects
Focal attenuation
More common in NTG
Degree of narrowing increases with amount of damage
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Retinal nerve fiber layer (RNFL)
RNFL: retinal ganglion cell axons covered by astrocytes and
bundled by Muller cell processes
Seen as bright fine striations fanning off the disc
Best evaluated with red-free filter
Can be difficult to appreciate in the blond fundus
Most visible infero-temporally and supero-temporally
Obscures details of underlying peripapillary retinal vascular
walls
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Clinical assessment of RNFL
• Requires
▫ Bright light
▫ Red-free filter
Green light produced by filter is absorbed by the RPE and
choroid, creating a dark background
The RNFL reflects the green light and is contrasted against the
dark background
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Normal RNFL • Bright, linear, striated appearance • Coarse texture • Casts white haze over underlying retinal structures and obscures
smaller blood vessels • Normal pattern: bright-dim-bright ▫ Pattern should be symmetric between S/I bundles and between
the two eyes • Brightness depends on ▫ Integrity of RNFL bundles ▫ Amount of pigmentation in RPE and choroid – blonde fundi, dull
RNFL ▫ Media clarity
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RNFL defects in glaucoma
• Selective damage to superior and inferior arcuate bundles
• Relative sparing of papillomacular and nasal bundles
• Defects appear as darker zones in areas of expected brightness
• Retinal vessels appear redder and darker
• Small vessels become more visible
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RNFL defects
Diffuse
Most common and most difficult to detect
Compare S/I and R/L striations: raked appearance and loss
of brightness
Peripapillary vessels appear bare
Underlying choroidal vessels more clearly visible
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RNFL defects: diffuse loss • Mild (D1) ▫ Striations are less bright and less coarse ▫ Medium size vessels apparent ▫ Small vessels still obscured
• Moderate (D2) ▫ Striations even less prominent ▫ Medium and small vessels clear
• Severe (D3) ▫ Few striations visible ▫ Deep retinal layers have grainy appearance ▫ Pseudosheathing of blood vessels: collagen walls become more visible
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RNFL: diffuse loss
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RNFL: diffuse loss
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RNFL defects: focal loss
Slit or wedge
Easiest to identify
Less common
Usually associated with notch at disc or current/prior
drance hemorrhage
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RNFL: focal loss
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RNFL defects: focal loss • Slit: ▫ Larger than an arteriole in width ▫ Travels back to the ONH
• Wedge: ▫ Expanding focal damage ▫ Associated with notching and arcuate VF defect
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Take-home points • C/D ratio is NOT the only factor to consider when evaluating the ONH
• You MUST give due diligence to the neuroretinal rim
▫ Focal defects
▫ Generalized thinning
• You MUST evaluate any asymmetry in the superior and inferior poles of
the same eye
• You MUST evaluate any asymmetry between the two eyes
• Always remember, glaucoma is cupping WITHOUT pallor
• Use imaging technologies and perimetry to evaluate suspicious nerves and
high-risk patients
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Optic nerve evaluation checklist
Measure size and shape of the ONH Evaluate size and shape of the optic cup Determine the vertical and horizontal C/D ratio Compare the expected C/D ratio based on vertical disc diameter Neuroretinal rim integrity/thinning/notching/pallor Superior vs inferior OD vs OS
Vascular changes: disc hemorrhages, nasalization of vessels, arteriole narrowing, optociliary shunt vessels, baring of vessels
Peripapillary atrophy RNFL defects: diffuse/focal
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Let us look at some nerves!
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Thank you!