The optic disc - NCBI

Brit. Y. Ophthal. (1976) 6o, 778

The optic disci: Classification

in glaucoma

R. A. HITCHINGSMoorfields Eye Hospital, City Road, LondonAND

G. L. SPAETHWills Eye Hospital, Spring Garden Street, Philadelphia I9I30, USA

The pale, cupped disc found in the final stages ofglaucomatous disease has been known from thetime of Von Graefe (I854). Since then manyobservers have described changes that occur at theoptic disc in chronic, simple glaucoma. There hasbeen particular interest in changes which mayoccur in the early stages of the disease.

Studies of the normal population have shownthat while there is a wide diversity in the appearanceof the normal optic disc, in a single subject (Armaly,I969; Fishman, I970; Kolker and Hetherington,1970; Portnoy, 1973) the two discs are remarkablysimilar (Witsiuk, I966; Kronfeld, 1970; Woodruff,1970; Portnoy, I973). In contrast, individuals withglaucomatous disease usually show manifest asym-metry of the two optic discs (Fishman, I970;Kolker and Hetherington, 1970).Many criteria have been used to describe the

glaucomatous optic disc. Important among these isthe ratio of the cup diameter to the diameter of theentire disc (Pickard, I923; Snydacker, I964;Hollows and McGuiness, I967; Armaly, i967, I968;Schwartz, I973; Tomlinson and Phillips, I974).This was initially measured horizontally, butrecently measurement of the vertical cup to disc(C/D) ratio has been stressed, after recognition thatchanges in the optic cup tend initially to affect thevertical diameter (Chandler and Grant, I965;Kronfeld, I967; Kirsch and Anderson, 1973;Weisman, Assif, Phelps, Podos, and Becker, 1973).

Stereoscopic examination of the optic disc in earlyglaucoma reveals signs which help to distinguishthe normal from the glaucomatous cup (Anderson,I975; Reed and Spaeth, I974). These signs areevidence for acquired tissue loss and account forthe asymmetry previously noted. Tissue loss mayappear in a variety of forms: thinning of the neuro-retinal rim, either localized or generalized; depres-sion or steepening of the walls of the cup (thetinted hollow (Reed and Spaeth, 1974) or saucer);

Address for reprints: R. A. Hitchings, FRCS, Moorfields EyeHospital, City Road, London ECIV 2PD

deepening of the cup exposing the lamina cribrosa(the 'laminar dots' sign (Reed and Spaeth, 1974));and change in the course of the retinal vessel whichis seen as a sharp change in direction ('kinking' orbayoneting (Reed and Spaeth, 1974)). In addition,the presence of localized regions of nerve fibre lossor 'gutters' has been demonstrated in some casesof early glaucoma by Hoyt, Frisen, and Neuman(1973).The aim of this paper was to assess systematically

glaucomatous discs and look for those features thatare commonly associated. As a result, five differenttypes of optic disc appearance are described.

In this paper the term glaucoma has been usedfor all cases in which the intraocular pressureexceeded 22 mmHg and glaucomatous cuppingwas visible on stereoscopic examination of the disc.This has meant including cases in which the opticdisc appeared normal by uniocular ophthalmoscopy,and even cases in which glaucomatous cupping wasvisible without detectable field loss.

Material and methodsThis study was based on analysis of stereoscopic discphotographs of 252 patients from the files of theGlaucoma Clinic at Wills Eye Hospital. The patientswere mostly cases of known or suspect glaucomaattending the Glaucoma Service. In addition, 25 normalpatients on the files of the Glaucoma Service wereincluded. The diagnosis was unknown at the time ofanalysis of the stereophotographs.Most photographs were taken within an I8-month

period using a Zeiss fundus flash II camera with a X 2-0adaptor. Stereoscopic photographs were obtained aftermaximal pupillary dilatation by photographing the clearoptic disc images obtained at each end of a horizontaltraverse of the camera body. This traverse was usually3 to 4 mm.

Slides were examined with a stereoscopic viewer.The stereo pairs of the two eyes were directly compared.Special note was made of identifying characteristicssuggestive of tissue loss.The following criteria were analysed:

The optic disc in glaucoma 779

THE VERTICAL CUP/DISC (C/D) RATIO

The 'cup' was defined in terms of configuration; itsextent was determined by drawing a hypothetical linevertically on the anterior surface of the disc from themost superior to the most inferior aspect of the discmargin; the segment of the line not in contact with thedisc surface was considered to be 'the cup'. The ratio(expressed in tenths) of that segment to the length ofthe entire line was the 'cup/disc ratio' (C/D). Pallor ofthe optic disc played no part in the assessment of theC/D ratio (Schwartz, 1973).

THE WALLS OF THE OPTIC CUP

The specific points checked were: degree of inclinationin the walls, variation in the slope of the walls of anyone cup, and difference between cups of the two eyesin each patient. The presence of a more steeply-sidedcup despite identical C/D ratios was considered sus-picious of enlargement of the cup.

THE DEPTH OF THE OPTIC CUP

The depth of the optic cup was described as 'normal','deep', or 'bean-pot'. 'Normal' depth referred to anoptic cup which did not show evidence of actual posteriorbowing of the lamina cribrosa itself; the cup, however,could extend as far posteriorly as the 'laminar dots'(taken to represent the lamina cribrosa) described byReed and Spaeth (I974). In a 'deep' cup the laminacribrosa appeared posteriorly bowed. A 'bean-pot' cup,so called because of its likeness to a spherical clay pot,was diagnosed when posterior displacement of thelamina cribrosa coexisted with undermining of theneuroretinal rim; in transverse section the walls andbase of the cup formed the major part of a circle. Therewas usually little difficulty distinguishing between aflat or a posteriorly-bowed lamina cribrosa. Similarly,although there was clearly a spectrum of changes,differentiation between the 'deep' and the 'bean-pot'cup was usually fairly straightforward. In those fewcases where differentiation between two descriptivetypes was not easy, the shallower type of cup depth waschosen.

THE NEURORETINAL RIM

The pallor and the width of the neuroretinal rims were

graded. The colour achieved with transparencies was

not an exact match with the colours seen on stereoscopicexamination, and pallor of the rim could not always bedifferentiated from the normal pinkish colour. As a

result, comments on colour were restricted to recordingwhether the neuroretinal rim was pale or pink. Thinningof the neuroretinal rim was far more easily quantitated,and ranged from being just noticeable to a completeabsence of rim tissue with extension of the cup to theouter disc margin. The size of the arc involved inthinning ranged from a localized segment (producing a

'notch') to circumferential thinning of the entireneuroretinal rim.

DISPLACEMENT OF THE RETINAL VESSELS

Distinction was made between a gradual curve of a

retinal vessel as it passed over the surface of the opticdisc and a sharp 'kinking' or change in the vessel'sdirection either in the same plane as the disc surface orat an angle to it. The gradual curve was considerednormal; the kink was thought to be an acquired changethat occurred secondary to enlargement of the optic cup.Kinking resulted in nasal displacement of the vessels,and was of most significance when it occurred at theouter margin of the disc.

PIGMENT CLUMPING

The presence or absence of pigment clumping aroundthe margin of the optic disc was noted.

NERVE FIBRE LAYER

The nature of the nerve fibre layer was observed as faras possible within the limits of the examination tech-nique. Where refractile lines taking the known patternof the nerve fibre layer (NFL) were visible the NFL wasthought to be present. If none of the gutters or groovesdescribed by Hoyt and others (1973) was visible theNFL was called 'intact'. If such a gutter was observedit was listed as a nerve fibre bundle defect (NFBD). Ifno NFL could be seen at all it was called 'invisible'.

Results

Stereoscopic photographs from 504 eyes of 252patients were analysed. The optic discs weredivided into two groups, normal and pathological,this second being subdivided into five types ofglaucomatous cupping (overpass, cupping withoutpallor of the neuroretinal rim, cupping with pallorof the neuroretinal rim, focal notching of theneuroretinal rim, and bean-pot cupping), whosecharacteristics will be described. The overallnumbers and characterizing features are seen inthe Table. Stereophotographs illustrating each ofthese examples may be seen in Figs 1-5.

CHARACTERISTICS OF DISC SUBTYPES

Normal discA disc was considered 'normal' in appearance ifthe neuroretinal rim was pinkish and of equalthickness throughout, or with its thinnest portionat the temporal margin on the horizontal meridianof the disc. There were no sharp deviations of anyretinal vessel where it traversed the disc surface.This type of disc usually had a C/D ratio of lessthan o 5, an optic cup of 'normal' depth (as definedabove), and a visibly intact nerve fibre layer. Whenthe two optic discs from any patient were highlysymmetrical, they were considered 'normal'; thislatter definition allowed optic discs with a C/Dratio greater than o 5, a sharply deviating retinalvessel, or a poorly visualized nerve fibre layer to beincluded in this normal group. The optic discs of

780 British Yournal of Ophthalnmology

Table Clinical features of glaucomatous discs

Tvpe No. Percentageof total

Vertical CID Cup depth-______ - IncidenceRange Mean Normal Deep Bean- of

pot overpassNo.)

I. Normal 231 46 o-o-6 0-3 223

2. Overpass vessels 44 9

3. Cupping withoutpallor of rim 124 25

4 Cupping withpallor of rim

5. Focal notching

6. Bean-pot

68 12

23 5

0-2-0-9 o-6 42

0-3-0-9 0-7 44

0-7-0-9 o-85 II

04-03 0-7 23

RimNotch pallor(No.) (No.)

6 - 27 0 0

Vesseldisplace- Pigment Nerve fibrement clumping bundle defect(Bayon- (No.)eting) (No.) (Per cent)(No.)

6 27 (I I) 222 Intact

2 44 3 3 1 3 21 (65)

76 4

57 -

FIG. I Overpass cupping; retinal vessels (dark arrows) pursuing a relatively undeviated course over the optic cup

(hollow arrows)

For satisfactory viewing these stereo pairs should be examined using a suitable convex sphere. With higher powers of sphere, fusion maybe obtained by decentring the spheres. To do this, increase the distance between them

all 25 patients. clinically considered normal fell into

this category.

Overpass cupping (Kronfeld, i967; Spaeth and

Hitchings, I975)

Where tissue loss within the optic nerve papillawas visible on stereoscopic examination, but without

gross enlargement of the optic cup, the phrase'overpass cupping' was used. This type of intra-papillary tissue loss occurred to a minor degree insome discs classed as 'normal'. More frequently, itinvolved the disc extensively, and the two discsasymmetrically, being the major anatomic abnor-mality visible on stereoscopic examination. In thesecases the retinal vessels could be seen pursuing a

12 0 0 I22 74 (6I)

I0 20 68 68 58 (82)

25 21 21 21 (91)

0 0 13 14 13 (92)14 3 0-9 -9 - - 14

g Invisible

24 Intact17 Invisible3 NFBD

82 Intact30 InvisibleI2 NFBD

6o Invisible8 NFBD

I Intact3 lnvis'ble

I9 NFBDI 3 lnvisibleI Intact

The optic disc in glaucoma 78I

FIG. 2 Cupping without pallor of the neuroretinal rim; glaucomatous cupping is suggested by localized (inferior)thinning of neuroretinal rim, steeply-sided walls to cup, an angulated course followed by infero-temporal vein aroundrim of cup, and, in this case, a splinter haemorrhage (arrow)

FIG. 3 Cupping with pallor of the neuroretinal rim; glaucomatous cupping associated with pallor of all or part ofneuroretinal rim. In this example neuroretinal rim (black arrows) has to be differentiated from adjacent peripapillaryatrophy. Pallor of neuroretinal rim may be seen in one segment (hollow arrows)

relatively undeviated course across the disc surface, displacement of retinal vessels. The true size ofapparently unsupported by disc tissue (this the optic cup was only apparent on stereoscopiccharacteristic of retinal vessels 'bridging' an optic examination. This type of tissue loss (overpasscup resembles the 'flyovers', or overpasses at road cupping) was considered as a separate class.junctions, hence the name). On direct ophthalmo-scopic examination, the optic cup with overpasscupping did not appear particularly enlarged as a Cupping without pallor of the nenroretinal rimmajor uniocular clue to the size of the optic cup is An optic disc with a pinkish neuroretinal rim but

782 British yournal of Ophthalmology

FIG. 4 Focal notching of the neuroretinal rim; neuroretinal rim is very thin in one localized segment. This is associatedwith localized enlargement of optic cup (arrowed). There is no evidence elsewhere on optic disc of enlargement of optic cup

FIG. 5 Bean-pot cupping; enormous size of optic cup, together with posterior bowing of laminar cribrosa andundermining of the neuroretinal rim resembles a 'bean pot' or gourd. Undermining of neuroretinal rim is emphasized bythe retinal vessels 'disappearing' behind the rim for part of their course (arrows)

with apparent enlargement of the optic cup wasconsidered to have cupping without pallor of theneuroretinal rim. The pertinent clues were markedthinning of the neuroretinal rim together withsteeply-sided walls to the optic cup and sharplyangulated vessels, resulting in an oval cup out ofproportion to that expected from the shape of theoptic disc (Portnoy, 1973). This appearance was in

some cases considered distinctive enough toindicate acquired glaucomatous cupping. In othercases the changes were less marked, evidence forglaucomatous cupping being obtained by compari-son of the two optic discs from one subject. Herethe following were taken as evidence for enlarge-ment: asymmetry of the surface area of the cup (adifference of 0>o2 in the C/D ratio was considered

The optic disc in glau0coma 783

significant); the steepness of the slope of the wallsof the cup, or the depth of the cup. These signs,taken to indicate an acquired change, were mostfrequently noted at the infero-temporal part of thecup. The supero-temporal area was the next mostfrequently affected, while enlargement in otherdirections occurred less often.Many of these optic discs could have been

considered normal if examined individually withoutevaluation of the fellow disc. It was only bycomparing the two discs that asymmetry becameapparent.

Cupping with pallor of the neuroretinal rim

In certain optic discs, cupping was combinedwith pallor of the neuroretinal rim-that is reducedvascularity of the neuroretinal rim which affectedpart or all of its extent. Also present were thosesigns described that suggested enlargement of theoptic cup and thinning of the neuroretinal rimsecondary to raised intraocular pressure. The nervefibre bundle layer was usually invisible.

Focal notching of the neuroretinal rim

In some eyes localized enlargement of the opticcup with thinning of the neuroretinal rim waspresent (notching), but without apparent cupenlargement elsewhere. This appearance wassufficiently distinctive to justify a separate category.In this series, the notch was usually in the infero-temporal quadrant. These eyes had the highestincidence of visible nerve fibre bundle defects.

Bean-pot cupping

Bean-pot cupping referred to the extreme enlarge-ment of the optic cup already described. Thisoccurred with or without pallor of the neuroretinalrim.There was a general tendency for the two optic

discs of any one patient to exhibit the same opticdisc type. This was especially true for those caseswith localized, or focal, notching and those with'bean-pot' cupping. When the same optic disctypes were not found, the following combinationsoccurred: normal + cupping with or withoutneuroretinal rim pallor; overpass + cupping withor without neuroretinal rim pallor.

DiscussionThe proportional representation of each type inthis series does not necessarily reflect the overallincidence in a glaucoma population. In the firstplace the population was highly selected becauseof the referral nature of the practice of one of us

(GLS). Furthermore, only those patients withtechnically excellent photographs were chosen foranalysis.There appear to be distinct morphological disc

types occurring in glaucomatous disease. Althoughclearly there was a definite overlap between groups,and some features were found common to morethan one type it was still possible to classify the discsinto five distinct morphological types. It was thepredominant feature (overpass, bean-pot, etc.)which decided placement. Different optic disc typescould have similar degrees of visual field loss andtherefore be at the same stage of glaucomatousdisease from the functional point of view (Hitchingsand Spaeth, in preparation).

It is always slightly suspect to state that anindividual optic cup has enlarged without docu-mentation in a longitudinal study. The inferencethat such enlargement does occur is based onprevious studies which reveal striking symmetrybetween the two discs in any one person (Fishman,I970; Portnoy, I973). Furthermore, there isevidence that the normal cup is horizontally ovalor circular (Kirsch and Anderson, I973; Weismanand others, I973). Vertical ovality of the cup whichexceeds that which could be explained on the basisof the vertical ovality of the disc itself suggests anacquired change (Kirsch and Anderson, I973;Portnoy, 1973; Weisman and others, 1973).An alternative explanation for an acquired

enlargement of the optic cup is that it is agerelated. It seems likely that the optic cup mayenlarge with age. Pickard (I948) noted this from alongitudinal study, while Schwartz, Reuling, andGarrison (I975) demonstrated an increase in thehorizontal C/D ratio with age by examiningstereophotographs of the optic disc. This is atvariance with the earlier work of Armaly (i967) whofelt, on the basis of uniocular ophthalmoscopy, thatthe optic cup did not increase with age. AlthoughSchwartz and others (I975) did not specificallymeasure it, it seems possible that the vertical C/Dratio does not enlarge more than the horizontalC/D ratio.The existence and extent of peripapillary pigment

clumping was noted (Primrose, I 972), but thePresent study shows that it is not pathognomic forglaucoma as it was found in 27 cases (i I per cent)of normal discs and in nine of these it occurred ineyes that were considered clinically normal.However, in agreement with the finding of Wilenskyand Kolker (I976) the incidence of pigmentaryclumping rose considerably with glaucomatousdisease, occurring in over 90 per cent of eyes withnotching of the optic cup and bean-pot cupping.In addition, in cases with bilateral glaucomatousdisease, the eye with the more advanced changes

784 British Jouirnal of Ophthalmology

tended to show a greater amount of pigmentaryclumping.

In those cases where it was possible to re-examinethe patients with red-free light (Hoyt and others,I973), we found that examination of stereophoto-graphs for defects with nerve fibre layer appearedto be just as accurate. Care was taken to differentiatetrue from pseudo 'gutters'. All cases in this serieswith nerve fibre bundle defects had glaucomatouscupping. The nerve fibre layer could not bevisualized at all in many patients with glaucoma,notwithstanding the presence of normal fields (onkinetic Goldmann field testing). Visibility was notimproved with red-free light. There would appearto be a non-specific depression of light reflexesarising from this layer which is associated with, andpossibly related to, raised intraocular pressure, and/or age.The highest incidence of nerve fibre bundle

defects was seen in cases with localized notching ofthe neuroretinal rim. There was always a corres-ponding 'dense' field defect on Goldmann perimetry,in marked distinction from discs in other groupswhere it could be difficult to state whether a fielddefect was present at all. In the group of eyes withcupping without neuroretinal rim pallor, it waspossible to detect changes in the appearance of theoptic nerve that suggested glaucoma, before nervefibre bundle defects could be seen. It appearedthat visualization of the nerve fibre layer was avaluable guide when present. That it could not beseen in many cases, despite full fields, suggests itsvalue in diagnosis is limited.The variable appearance of the optic nerve in

glaucoma suggests a different response of the nerveto differing disease processes. This may reflectanatomical differences between optic nerves, varia-tion in the duration of the height of the raisedintraocular pressure and coexistence of cardio-

vascular and haematological disease. These factorsmay act singly or in varying combinations. This isborne out to some extent by our knowledge of thenatural course of glaucomatous disease. Childrenand young adults are known to develop glauco-matous cupping and visual field loss after acomparatively short time. The flame-shapedhaemorrhage may indicate sudden visual field loss(Drance and Begg, 1970). Conversely some nervesappear capable of withstanding many years ofincreased intraocular pressure without damage.The appearance of the glaucomatous disc may beaffected by many factors. Recognition of differingmorphological types may be a step towards recog-nizing the predominating factors in each case.

Summary

Five different descriptive types of glaucomatousoptic discs are described, based on the examinationof X 2 magnification stereophotographs of 252patients from the files of the Glaucoma Service atWills Eye Hospital. The method of analysis isdescribed in detail. These types include: overpasscupping, cupping without pallor of the neuroretinalrim, cupping with pallor of the neuroretinal rim,focal notching of the neuroretinal rim, and bean-potcupping.These morphological types may be caused by

variations in factors contributing to the pathogenesisof glaucomatous eyes. Recognition of these differingtypes may help in determining the factors in eachcase.

We thank Mr R. J. Smith, and Professor J. Gloster fortheir advice.The investigation was supported by National Institute

of Health Research Grant No. EYoo67704 from theNational Eye Institute.

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The optic disc in glaucoma 785

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