Aspects of optic nerve head evaluation in POAG.And nerve fibre layer analysis

1. Optic nerve Head &Optic nerve Head &
retinal nerve fiberretinal nerve fiber
EvaluationEvaluation
Dr Milind M SabnisDr Milind M Sabnis
Date: 2 Sept 2018Date: 2 Sept 2018

2. IntroductionIntroduction
 The glaucomatous changes are in theThe glaucomatous changes are in the intra-intra-
papillary & para-papillarypapillary & para-papillary region of the opticregion of the optic
nerve head & retinal nerve fiber layer.nerve head & retinal nerve fiber layer.
 Intra-papillary changes –Intra-papillary changes –
-disc size-disc size
-disc shape-disc shape
-rim size & cup size-rim size & cup size
-rim shape(Vessel signs)-rim shape(Vessel signs)

3.  Parapapillary characteristicsParapapillary characteristics ––
-retinal nerve fiber layer(RNFL)-retinal nerve fiber layer(RNFL)
-haemorrhages-haemorrhages
-vessel diameter-vessel diameter
-para-papillary atrophy( alpha & beta)-para-papillary atrophy( alpha & beta)

4. Retinal nerve fibersRetinal nerve fibers
 There are 1.2 million RNFs which formThere are 1.2 million RNFs which form
the optic nerve head(optic disc)the optic nerve head(optic disc)
 Within the retina -Within the retina -

5.  Within the optic nerve head –Within the optic nerve head –

6. Optic nerve headOptic nerve head

7. Glaucomatous damageGlaucomatous damage
 Glaucomatous damage results in characteristicGlaucomatous damage results in characteristic
signs in retinal nerve fiber layer,parapapillarysigns in retinal nerve fiber layer,parapapillary
area & the optic nerve head.area & the optic nerve head.

8.  Retinal nerve fiber layerRetinal nerve fiber layer :-:-
-defects may be local or diffuse.-defects may be local or diffuse.
-early localised damage is characterised by slit-early localised damage is characterised by slit
defects in the retinal nerve fiber layer.defects in the retinal nerve fiber layer.

9.  As glaucoma damage progresses,theAs glaucoma damage progresses,the
defects become larger.defects become larger.
 The atrophic area becomes darker,due toThe atrophic area becomes darker,due to
enhanced visualisation of the RPE.enhanced visualisation of the RPE.

10.  Parapapillary changesParapapillary changes :-:-
-chorioretinal atrophy surrounding the optic-chorioretinal atrophy surrounding the optic
disc,consists of 2 zonesdisc,consists of 2 zones
-an inner ‘beta’ zone,bordering the optic disc &-an inner ‘beta’ zone,bordering the optic disc &
surrounded by ‘alpha’ zone.surrounded by ‘alpha’ zone.

11.  The beta zone –The beta zone –
-chorioretinal atrophy with visibility of sclera &-chorioretinal atrophy with visibility of sclera &
large choroidal blood vessels.large choroidal blood vessels.
 The alpha zoneThe alpha zone ––
-displays irregular hyper & hypo-pigmenttation-displays irregular hyper & hypo-pigmenttation
of the retinal pigment epitheliumof the retinal pigment epithelium..

12. The Optic DiscThe Optic Disc
 The optic disc is slightly oval.The optic disc is slightly oval.
 Myopics have large optic disc as compared toMyopics have large optic disc as compared to
hyperopics.hyperopics.
 An abnormal shape correlates with an increasedAn abnormal shape correlates with an increased
incidence of corneal astigmatism & amblyopia.incidence of corneal astigmatism & amblyopia.

13. Normal /Abnormal…..?Normal /Abnormal…..?

14.  In normal eyes, the optic disc is verticallyIn normal eyes, the optic disc is vertically
oval & the optic cup is horizontally oval.oval & the optic cup is horizontally oval.

15. ‘‘ISNT’ ruleISNT’ rule
 The neuro-retinal rim is widest in theThe neuro-retinal rim is widest in the
InferiorInferior disc regiondisc region SuperiorSuperior discdisc
regionregion NasalNasal disc areadisc area TemporalTemporal
disc areadisc area

16.  In glaucoma,the neuro-retinal rim is lost in allIn glaucoma,the neuro-retinal rim is lost in all
sections of the of the optic disc, depending uponsections of the of the optic disc, depending upon
the stage of the disease.....the stage of the disease.....
Infero-temporalInfero-temporal Supero-temporalSupero-temporal 
Temporal horizontalTemporal horizontal Infero-nasalInfero-nasal 
Supero-nasalSupero-nasal

17. Disc haemorrhageDisc haemorrhage
 Disc hemorrhage is a common sign of OpticDisc hemorrhage is a common sign of Optic
nerve damage.nerve damage.
 Present in 4-7 % of glaucomatous patients.Present in 4-7 % of glaucomatous patients.

18.  In early glaucoma,they are usually present inIn early glaucoma,they are usually present in
infero-temporal & supero-temporal tegion.infero-temporal & supero-temporal tegion.
 They are suggestive ofThey are suggestive of glaucoma progressionglaucoma progression..
 They can also present in conditions like bloodThey can also present in conditions like blood
dyscrasias,DM,hypertension.dyscrasias,DM,hypertension.

19. Glaucomatous optic nerve damageGlaucomatous optic nerve damage
 Shape of the neuro-retinal rim –Shape of the neuro-retinal rim –
-NRR thinning-NRR thinning
-peripapillary atrophy-peripapillary atrophy
 Size of optic cup in relation to optic disc :-Size of optic cup in relation to optic disc :-
-glaucomatous cupping ( CD > 0.3)-glaucomatous cupping ( CD > 0.3)
-asymmtery in CD in fellow eyes( difference > 0.2)-asymmtery in CD in fellow eyes( difference > 0.2)

20.  Occurrence of retinal nerve fiber layer defects &Occurrence of retinal nerve fiber layer defects &
hemorrhages.hemorrhages.
 Decreased diameter of the retinal arteriolesDecreased diameter of the retinal arterioles
including the presence of focal arteriolarincluding the presence of focal arteriolar
narrowing.narrowing.
 Enlargement of optic cup & loss of neuro-Enlargement of optic cup & loss of neuro-
retinal rim may also be found in arteritic antretinal rim may also be found in arteritic ant
ischaemic optic neuropathy & in pts withischaemic optic neuropathy & in pts with
intrasellar tumours.intrasellar tumours.

21. Subtypes of glaucomatous damageSubtypes of glaucomatous damage
 Type I – focal ischaemicType I – focal ischaemic
 Type II – myopic glaucomatousType II – myopic glaucomatous
 Type III – senile scleroticType III – senile sclerotic
 Type IV – concentrically enlargingType IV – concentrically enlarging
 Type V – mixedType V – mixed

22. Newer imaging techniquesNewer imaging techniques
 These newer techniques focus on early diagnosisThese newer techniques focus on early diagnosis
of glaucoma.of glaucoma.
 These are –These are –
-stereo-photogrammetry-stereo-photogrammetry
-raster photography-raster photography
-OCT-OCT

23. Stereo-photogrammetryStereo-photogrammetry
 Utilises the basic principle of stereopsisUtilises the basic principle of stereopsis
 Disparity between corresponding points ofDisparity between corresponding points of
stereo pair images are used to generate contourstereo pair images are used to generate contour
lines & 3D contour maps.lines & 3D contour maps.

24. Confocal laser scanningConfocal laser scanning
 It is a technique for obtaining high resolutionIt is a technique for obtaining high resolution
images by using a focused laser beam to scanimages by using a focused laser beam to scan
over the area of the fundus.over the area of the fundus.
 Instruments :-Instruments :-
-HRT-HRT
-Rodenstoc 101 confocal scanning laser-Rodenstoc 101 confocal scanning laser
ophthalmoscopeophthalmoscope
-Nerve fiber layer analyser.-Nerve fiber layer analyser.

25. Heidelberge retinal tomographHeidelberge retinal tomograph
 It is a confocal scanning laserIt is a confocal scanning laser
ophthalmoscope system which providesophthalmoscope system which provides
3D image & quantitative assesment of3D image & quantitative assesment of
optic nerve head.optic nerve head.
 In printout 2 types of images areIn printout 2 types of images are
provided,topography image & reflectanceprovided,topography image & reflectance
image of the fundus.image of the fundus.

28.  Contour lineContour line :-:-
-this line limits the optic disc or represents the-this line limits the optic disc or represents the
optic disc margin.optic disc margin.
-it is represented from 0-it is represented from 000
to 360to 36000
-0-000
being the horizontal temporal point & runsbeing the horizontal temporal point & runs
clowckwise in rt eye & anticlockwise in the leftclowckwise in rt eye & anticlockwise in the left
eye.eye.
-therefore 90-therefore 9000
is superior,180is superior,18000
is nasal,270is nasal,27000
isis
inferior & 360inferior & 36000
is temporal.is temporal.

29.  Standard reference plane :-Standard reference plane :-
-it is defined as the plane situated 50u deeper to-it is defined as the plane situated 50u deeper to
the avg height of the 6the avg height of the 600
segment of the contoursegment of the contour
lineline between 350between 35000
to 356to 35600
-this segment is supposed to represent the-this segment is supposed to represent the
papillomacular bundle which is expected topapillomacular bundle which is expected to
remain stable during course of glaucoma.remain stable during course of glaucoma.
-all the structures above SRP within the contour-all the structures above SRP within the contour
line is considered as NRR & below SRP is opticline is considered as NRR & below SRP is optic
cup.cup.

30. Various parts of the HRTVarious parts of the HRT
 General information :-General information :-
-patients name,age,ID no-patients name,age,ID no
-dioptric power used to focus the image-dioptric power used to focus the image
-scan depth-scan depth
-IOP-IOP

31.  Topography image :-part ITopography image :-part I
-this is 2D representation of the 3D image in-this is 2D representation of the 3D image in
colour coded map.colour coded map.
-the darker colour represents more elevated-the darker colour represents more elevated
surface & lighter colour represents depressedsurface & lighter colour represents depressed
surface.surface.
-the area within the contour line represents the-the area within the contour line represents the
optic disc,where as red area is cup.optic disc,where as red area is cup.
-the green(uniform height) & blue(sloping)-the green(uniform height) & blue(sloping)
represents the NRR.represents the NRR.

33.  Horizontal height profile graph – part IIIHorizontal height profile graph – part III
-Y axis denotes the cup depth & Z-axis denotes-Y axis denotes the cup depth & Z-axis denotes
the rim thickness.the rim thickness.
- Red horizontal line represents the SRP.- Red horizontal line represents the SRP.
- Vertical height profile graph –part IV- Vertical height profile graph –part IV
-two black represents the disc margin & vertical-two black represents the disc margin & vertical
line shows the SRP.line shows the SRP.

34.  Reflectance image :- VReflectance image :- V
-The image is used to draw the contour line.-The image is used to draw the contour line.
-the optic disc is divided into 6 sectors –-the optic disc is divided into 6 sectors –
temporal,sup temporal,sup nasal,nasal inftemporal,sup temporal,sup nasal,nasal inf
nasal,& inf temporal.nasal,& inf temporal.
--MarksMarks :- the green mark – within normal limits:- the green mark – within normal limits
- yellow mark- borderline- yellow mark- borderline
-red mark – outside normal limit.-red mark – outside normal limit.

35.  Mean height contour graphMean height contour graph :-part VI:-part VI
-located below the reflectance image.-located below the reflectance image.
-the black line represents the mean peripapillary-the black line represents the mean peripapillary
retinal surface ht.retinal surface ht.
-red horizontal line represents the SRP.-red horizontal line represents the SRP.

36.  Moorfields regression analysis :- part VIIMoorfields regression analysis :- part VII
-in the form of 7 vertical bars.-in the form of 7 vertical bars.
-the 1-the 1stst
bar represents the global(total optic disc)bar represents the global(total optic disc)
analysis & the remaining 6 represents theanalysis & the remaining 6 represents the
analysis of the 6 sectors.analysis of the 6 sectors.
-each bar has green segment-each bar has green segment % of NRR area.% of NRR area.
-red segment-red segment  cup area.cup area.
-each column has 4 horizontal lines-each column has 4 horizontal lines
-the upper line represents the 50-the upper line represents the 50thth
percentile pointpercentile point
of normal.of normal.

37.  Three horizontal lines are clustered belowThree horizontal lines are clustered below
-the uppermost as 95%,middle as 99% & lower is-the uppermost as 95%,middle as 99% & lower is
99.9% representing the 9599.9% representing the 95thth
,99,99thth
,99.9,99.9thth
persentilepersentile
points respectively.points respectively.

38.  Stereometric parametersStereometric parameters :-part VIII:-part VIII
-here the values of various stereometric parameters-here the values of various stereometric parameters
are in the graph.are in the graph.

39. Ocular coherence tomographyOcular coherence tomography
 It produces cross sectional image of retina &It produces cross sectional image of retina &
optic nerve with a resolution of 10u.optic nerve with a resolution of 10u.
 It requires clear media & pupillary dilatation forIt requires clear media & pupillary dilatation for
good images.good images.
 In glaucoma the retinal nerve fiber layer(RNFL)In glaucoma the retinal nerve fiber layer(RNFL)
thickness in peripapillary area,optic disc analysisthickness in peripapillary area,optic disc analysis
& RNFL thickness in macular area to be studied.& RNFL thickness in macular area to be studied.

42.  The OCT signal from a tissue layer is aThe OCT signal from a tissue layer is a
combination of its reflectivity & absorption &combination of its reflectivity & absorption &
scattering properties of the overlying layers.scattering properties of the overlying layers.
 The maximal reflection & back scattering isThe maximal reflection & back scattering is
represented by red-yellow colours.represented by red-yellow colours.
 The minimal signals are represented by blue-The minimal signals are represented by blue-
black colours.black colours.

43. OCT in glaucomaOCT in glaucoma
 RNFL thinning is the 1RNFL thinning is the 1stst
sign of early glaucoma.sign of early glaucoma.
 The main uses areThe main uses are ––
-to evaluate the RNFL for early glaucoma(pre--to evaluate the RNFL for early glaucoma(pre-
perimetric)perimetric)
-to detect,follow,study the macular changes in-to detect,follow,study the macular changes in
hypotony induced maculopathy after glaucomahypotony induced maculopathy after glaucoma
Sx.Sx.
-to evaluate CME after combined-to evaluate CME after combined
cataract/glaucoma Sx.cataract/glaucoma Sx.
-to evaluate optic nerve head tomography in-to evaluate optic nerve head tomography in
glaucoma patientsglaucoma patients