How Does Resetting Intraocular Pressure Help Optic Nerve Function?

GEORGE L. SPAETH, MARY LUCY How does resetting MARQUES PEREIRA intraocular pressure help optic nerve function?

There are two quite separate parts of this article: presumed normal in whatever is being the first deals with fact, the second, theory. The considered: disc topography, electrical subject is whether a resetting of the level of responsiveness, visual field, etc. But it should be intraocular pressure (lOP) has a beneficial effect stressed that the relationship between the in glaucoma, and if so, how it causes a benefit. different measures is complex: the disc can Regarding fact, it has been known since 1869 'improve' topographically at the same time as that lowering lOP can benefit a person - such as the visual field is deteriorating, and the disc Katherina - with glaucoma, in whom may seem structurally unchanged despite disappearance of headache and improvement in improvement in the visual field. appearance of the optic nerve head were the consequence of lowering pressure.1 It is now Evidence that glaucoma improves when lOP is known that 'improvement' in disc topography lowered is a common occurrence following lowering of the IOp,l-12 and that improvement in visual Optic disc topography function also occurs.5,13-22 This is established An improvement in the appearance of the optic fact. Much, however, is not established: disc of humans, manifested by a decrease in the diameter of the cup, shallowing of the cup, • In whom will such improvement occur? decrease in cup volume, widening of the neural

• What predisposes to such improvement? rim, and a decrease in signs of venous stasis,

• What are the mechanisms that account for can occur consequential to lowering IOPS.2-12 the improvement? Such improvement is common, indeed routine,

Evidence of improvement is seen both in in infants with cupping caused by elevated individuals and in populations. The intraocular pressure,23,24 but it also occurs in 1,2). improvement caused by lowering lOP from adults, including the elderly (Figs. Factors 80 mmHg to 15 mmHg, in a person in whom associated with such an improvement suggest 3). lOP acutely went from 15 to 80 mmHg, is mechanisms to account for the change (Table obvious to all. But the matter to be considered The appearance of the disc varies25 and is here is whether lowering lOP is of benefit in related to its diameter (the circumference of the chronic glaucoma with lesser magnitudes of scleral ring), the anterior-posterior position of pressure elevation. Let us define our terms so the lamina, the curvature of the lamina, the we can communicate most clearly: number and size of the optic neurons, the amount and nature of other cellular material Glaucoma is ocular tissue damage at G.L. Spaeth Glaucoma (astroglia), the extracellular material and the M.L. Marques Pereira least partly related to pressure within the eye. vascularity (Table 2). William and Anna Goldberg This is an arbitrary definition, but if the Glaucoma Service The position of the anterior portion of the & pressure-related aspect is removed, every case Research Laboratories optic nerve is a function of the pressure within of an optic neuropathy becomes glaucoma. If Wills Eye Hospital the eye anterior to the lamina cribrosa, the Philadelphia loss of function must be present to have pressure posterior to the lamina cribrosa, and Pennsylvania, USA 'glaucoma' one eliminates the evolving stages of the compliance of the lamina cribrosa. The disc the disease, and considers only the late stages of G.L. Spaeth is a plastic structure, related to the presence of the condition, because topographical change Professor of Ophthalmology elastin in the lamina. With increasing age the Jefferson Medical College precedes functional change. amount of elastin decreases. Also, the nature of Philadelphia A careful distinction must be collagen changes with age and perhaps with PA 19107, USA Improvement the made between an improvement in a finding and presence of glaucoma?6-29 Changes in lOP, George L. Spaeth, MD � an improvement in function, cellular or then, either up or down, can be associated with Wills Eye Hospital personal. These are related, but different changes in the position of the lamina 900 Walnut Street measures. For example, the rim area of the disc cribrosa.30-33 In the enucleated eye, raising lOP Philadelphia 5 50 PA 19107, USA may become thicker or the cup shallower, but from to mmHg displaces the surface of the that does not prove that neurones function optic nerve head 36 fLm posteriorly.31 As the Tel: +1 (215) 928 3197 Fax: +1 (215) 928 0166 better or that the person sees better. By lamina moves anteriorly or posteriorly, it has e-mail: [email protected] 'improvement', here, we mean a return towards the capacity to traumatise neurones directly by

Concentric cupping becoming worse with [OP near 40 mmHg Fig. 1. (a, b), but becoming less post-operatively when [OP pressure was 18 mmHg (c, taken years after b). (c) 2

compression injury or traction on straight or kinked The size of the optic cup is related to the size of the neurones,34 or indirectly due to arterial ischaemia or optic nerve head.43 A decrease in the size of the scleral venous stasis.35-42 Lowering lOP, then, may presumably ring, with a consequent decrease in the diameter of the exert a beneficial effect if the anterior optic nerve has optic nerve head, can occur, especially in infants, been posteriorly displaced secondary to lOP. The following lowering of lOP?3 Thus, improvement in disc absolute level of lOP may be immaterial. The critical topography in infants following a decrease in lOP is a factors are the relationship between the level of lOP combination of anterior movement of the lamina and a anterior to and posterior to the lamina, and the ability of decrease in disc size. This mechanism has not been that lamina to be deformed due to its compliance extensively studied in adults, but is certainly less of a characteristics. Laminar deformation may also have factor than in infants. effects on the vessels that pass through the tissues, and a The width of the neural rim of the optic nerve is a restoration of the normal position of the lamina may be function of the size of the scleral ring and the number associated with improved haemodynamics, assuming and nature of the neurones. The scleral ring can be vascular changes are not permanent. affected by lOP, as already discussed.23 Most normal

(a) (b)

(a), (b) The optic disc of this 60-year-old man showed less cupping following reduction of [OP (b). Fig. 2.

477 Factors predisposing to improvement of optic disc topography Mechanisms for improvement in disc appearance, in Table 1. Table 3. association with lowering of intraocular pressure Young age Short duration of optic disc damage Anterior displacement of lamina cribrosa Marked fall in intraocular pressure Decrease in the diameter of the disc Less advanced optic disc damage Healing of damage neurones Concentric cupping without focal change of optic disc Increase in connective tissue (late) Oedema (early and transient) Oedema (chronic with hypotony) eyes have roughly the same number of optic neurones; Neogenesis of neurones this number decreases with age.44-47 The neural ring may become thinner in advancing age because of this been established that lowering lOP by, for example, apparently obligatory loss of neurones, although this 15 mmHg is more beneficial in a particular specific change, if real, is not marked.48 It is logical to assume that population or particular individual than lowering lOP by damaged neurones that recover when the damaging 5 mmHg. It is also not known whether considering the factors are relieved may regain their normal bulk, and, as lowering in terms of a percentage of absolute fall is more such, cause a thickening of the neural rim. relevant. However, improvement appears to be unlikely Astroglia comprise a portion of the optic nerve head when lOP falls by less than 30%.5 One study, which tissue.49 These cells are also damaged by factors that affect reviewed stereophotographs and visual fields, the neurones.50 As they recover, which they presumably demonstrated that of patients having at least a 30% do when damage is not fatal, they may cause a decrease in cupping. In patients with far-advanced damage such a reduction in lOP, 30% had improved disc appearance 5 change appears to occur occasionally, as demonstrated by and 40% had improved visual fields. In another study, a marked 'filling in' of the cup, usually unassociated with using computer analysis of optic disc stereophotographs, improvement in visual function (Fig. 3). improvement in all optic disc parameters was found in 8 6 Acute oedema may cause an immediate decrease in of 13 eyes having a mean lOP reduction of 48%. Using 'cupping' following a decrease in lOP (Fig. 4). While this the same technique another study detected increased tends to be more prominent in eyes with lesser degrees of neuroretinal rim area in 44% of patients undergoing disc change, it can occur in eyes with advanced optic glaucoma surgery? Raitta and colleagues6 showed, using nerve damage.51 the Heidelberg Retina Tomograph (HRT) to study Lastly, the possibility of neuronal neogenesis can no changes in optic disc topography after glaucoma surgery longer be dismissed, since several investigators have in 9 patients, a reduction in optic disc cup volume in all now established that central nervous systems neurones but one of the eyes that had at least a 30% lOP reduction. 5 53 can regenerate. 2, This, however, is not a likely The mean cup depth was reduced significantly for this explanation for the topographic improvement in adults. group after 3.7 months of follow-up. The cup:disc ratio Discs which deteriorate by concentric cupping (Fig. 1) was significantly reduced for a subgroup of patients after are more likely to show improvement than those with 12 months, and the surface height of the retinal nerve focal changes (Figs. 5, 6). Experimental glaucoma caused fibre layer was increased. However, no significant by elevating lOP usually causes concentric cupping, correlation between the amount of fall of lOP and the rather than focal loss. It may be, then, that concentric presence of a disc improvement, was found,14 in cupping represents a mechanical type of disc damage agreement with the results of Lesk and colleaguesll and and that elimination of the mechanical cause (elevated Irak and colleagues.9 Thus, there is an unclear lOP) therefore allows the plastic nerve head to recover. relationship between change in disc appearance and the With focal changes the pathology is presumably not just amount of pressure lowering. It appears clinically that pressure-elevation related, so that displacement of the lowering pressure below about 8 mmHg does not give lamina may play less of a role in these cases. The relation between the amount of lowering of lOP added benefit, but this is not established. Burgoyne has discussed the theoretical relationships and disc improvement is not clear. The greater the 3 5 decrease in lOP, the greater the likelihood that disc between lOP and cupping, 2, 2 reminding us that even topography will show an improvement. However, the 'normal' lOP constitutes a substantial force on the shape of the curve of this relationship has not been neurones and the connective tissue. defined for populations or individuals. Thus, it has not

Factors affecting the appearance of the optic disc Table 2. Diameter of the nerve head (circumference of the scleral ring) Nerve fibre layer Anterior-posterior position of the lamina The thickness of the retinal nerve fibre layer is related to Intraocular pressure the number of retinal ganglion cells.53 A change in Cerebrospinal fluid Number and size of neurones thickness, then, may reflect a change in the number of Other cellular components ganglion cells. Lowering lOP has been associated with Extracellular considerations increase in nerve fibre layer thickness,6,54,55 which may V asculari ty be a sign of an increased number of ganglion cells.

478 (a) (b)

(a), (b) There is an apparent improvement in the disc, with less cupping following lowering of the (b) in a woman in her seventies. The Fig. 3. rop filling-in' of the cup took years to develop, during which time the visual field worsened.

Visual field interpretation. Because of this variability the changes in the field must be great or the number of patients showing Many authors have noted improvement in the visual an improvement must be great for such changes to be field in association with lowering of IOp.5,14--20 This may considered real. Nevertheless studies such as the occur in response to acute changes, such as with single Glaucoma Laser Trial (GLIfl,22 strongly suggest that drop therapy13 or single doses of an oral carbonic chronic treatment can be associated with improvement in anhydrase inhibitor.14 Changes may also occur the visual fields in patients with moderate or early chronically. A relation between the amount of lowering primary open-angle glaucoma. In the GLI eyes were of lOP and the amount of visual field improvement has randomised to initial therapy with laser or medication. been shown.19 Whether these apparent improvements Both groups showed a reduction in lOP in response to are real is complicated by the normal variability of visual treatment, though the eyes initially treated with laser field testing results, the learning curve of the subject trabeculoplasty had a statistically greater reduction than being tested, psychic changes, and difficulties in eyes initially treated with medication.31 Both groups also

(a) (b)

(a)-(c) Transient oedema of the disc (b) may occur following Fig. 4. lowering of and needs to be distinguished from lasting change, as rop, (e) seen in (c).

479 (a) (b) (a), (b) Widening of the rim may occur in some patients with focal change. Fig. 5.

RE LE RE LE

Nome Nome AZ AZ Do'e 1-72 Do,e 11-14

t5 P\Ipi DID... .,.' � "' ...... _ --1.. c..._ � c....-� """" ---- V*M ______��o "- ...... 4 3 Z I 4 .l 2 , 0 ,

• •

y (a) (b)

{C) (d) (a-d) When focal cupping is marked, improvement in disc appearance may not be noted, even in the face of substantial improvement in the Fig. 6. visual field.

showed a statistically significant improvement in visual 'Resetting' intraocular pressure: 'stabilising' versus field, and this was significantly greater in the eyes with 'lowering'

the greater lowering of lOP. The two groups were in It is entirely reasonable to believe that stabilisation of lOP other ways comparable, suggesting that the greater may itself decrease the tendency of neurones to be improvement in visual field was a consequence of the damaged in glaucoma. Neuronal damage may not be

greater lowering of lOP?! Presumed mechanisms for Mechanisms for improvement in blood flow in association improvement in visual field are listed in Table 4. Table 5. with 'resetting' of intraocular pressure Increased perfusion pressure related to lower intraocular pressure Less direct compression of blood vessels Mechanisms for improvement in the visual field Table 4. Less compression of vessels due to less distortion of lamina Relief of direct compression of neurones Improved rheology (less clotting, lower viscosity, etc.) Relief of 'kinking' Less episodic stretch on vessels and less release of Restoration of normal blood flow vasoconstrictive agents Restoration of normal nutrition Decrease in vascular effects of pharmacological agents used in Removal of waste and toxins treatment due to decreased use of these agents

480 (a), (b) Fluorescein angiography demonstrated an improvement Fig. 7. in blood flow following lowering of lOP in these two adults. Note the more rapid and more complete filling of the optic disc vasculature when lOP pressure was lowered around 50% from the initial leve/. (Courtesy of the American Ophthalmological Society.)

(a)

(bi) (bii) solely a function of a pressure 'higher' than the neurones substances and consequent localised vasospasm. The can tolerate, but may theoretically be caused by vasospasm then becomes the damaging mechanism, but oscillating lOP. Motion of the anterior surface of the optic the cause of the vasospasm is the change in the position nerve, either anteriorly or posteriorly, may stretch the vessels, causing release of endothelial vasoactive of the blood vessels caused by the unstable lOP.

481 TOTlll OEYIATIIIM PAmRN DEVIATION

GHT: O1JTSID NORMAL L1ms 5.B 13 8112 M" APR FL 1m FN FP 81 13 2i1tl5 . . . .. � . 94 . .

......

, . :::: .. . PSD SF CPSD FOV MO ... M 7.19 ( B.5Y. 1.25 DB 7.B7 ( � M I.M DB P DB P &.5X

27 CHT: OUTSID NOR"AL L1ms S.8 "" 8121 FN 8111 8119 AP FL FP 2i1tl5 R 94 26 25 . . . . � (fl)3& ( n) 27 29 27 29 � • • 26 28 (27) 31 (27) ( ��J 31 (n) 18 •• •• 27 31 33 28 . . ------:::::::::::::::: , , , :: 32 23 ... 8 - ••• � • •• ' ' (])32 m)-26 ------=-=:...... :- 33 35 134 31 2 (35)34 34)33 32 28 34 3 (��) (BJ . 32 . . . . 31 · ...... : h ...... : :: : : (J!) 33 dl) ...... : . 32 28 ...... : . : 31 24 . : : :: :: : , : . : ' ' : (24) PSD PS FDV : :: :: 110 SF C D 08 :::: :: : :: ... 2.48 ( ( 38 : DB P II!'/, 6.22 DB P 8.57. e.97 DB S.13 DB P ( &.5X

CHT: OUTS! N A 5.& "M 28 ORM L LIM ITS JUt FL 8t2B FM 81IB FP 114 28115 .

.. 94 .

.. . � . �

� • • • • •

...... :: . . . .· ...... : :......

.. . PSD CPSD FOV . .:::::: 110 SF . ... P ( 4.58 ( 38 DB B.71 D8 4.76 DB IX 1.23 DB DB P 1.51.

LIMITS i.& CHT: OUTSID MORItA\. 5.8 "" FL 1128 FM 1/8 FP 817 28115

�

.. : ,i;,:: ,n"ll, . . � • • ' ,, � . :: . " . : :;: :� :: . .. .. -- -. • • • . ! �-f � . -----___:_------� . - : _ii__!"__:_:"_:',_: :_::_�_:._ � �-(:,il :�):�:)�) '�) :: 'U"l! --- .�- .-. - .--.- ...... - :�-::-:"-!: !: ' -- -:, �! ·- ...... : : : : :: ::: : :: . : . . ::::::: ::: . . :. . - -, ' •...... : : 32 32 31 32 33 33 3B 38 . . • • • . ) . . . . . : .: : : . : : :: (3 (33) . . . : : : . : 32 31 31 3B 29 3B ...... : (3 ) 3B (32) . : :: 38 33 28 ...... "0 PSD SF . . FOV . CPSD ...... ::::::::: P ( ( 08 P ( 37 DB ...... : ... 2.36 DB II'I. .. . 3.69 DB P 5X 1.49 DB 3.33 IX .. ..

8. For legend see 485. Fig. p.

Stabilising lOP may also eliminate a 'push ...pull' type optic nerve damage when lOPs range between 15 and

of compression injury of the neurones. It is entirely 25 mmHg, with a mean around 20 mmHg, and yet not possible, then, that an individual may have progressive have further deterioration following filtering surgery

482 5.8 FH 819 FP 811& HH 28115

24 2& 1 1 19 . . " � ,. ,. I) 27 " .. 25 29 2& 25 (I • .. •

(m l23H(I) ...... 24 J2 29 31 . 28 31 2& 18 • • 11 (291 34 31 (29128 lB) .. 29 32 25 7 (8 ,. •• � • •• CIS) 35 CIt-HI) 38 (8 33 �� 1�4 32 38 28 ( ) 4) (��) ...... :::: .. : . . . . 34 32 (��) 34 : 35 38 28 . . '...... :::::: ...... : : · . . . : ...... :: : . . . . �2 31 33 4 31 �2 . :: : . : : 3 :: :.:: . : : :: : . . . ( 8) 3 ( 8 ) :::::: . . : . . 8 32 29 38 :: :::: :: FOV : PSO :: MO SF CPSO 39 DB DB P &.B& 08 P ( 8.5Z DB P ( - 2.27 ( 18"1. 1.3B DB 6.78 8.SY. 15 HORHAL lIftITS GHT: OUTS ID FL 8128 8118 5.1 "" FH FP illS 28115 1 24 24 3 29 2 • • 27 ( �h(�I) 1 ( nllU 28 32 �I 32 33 (B) 28 (�I) " "

J 32 .. U �6 M U 32 " " D • � • � ,. (23tl29ll 19)------32 (I 35 134 35 32 32 J2 2 ( �s 7)4 3336) 32 32 3 (n) (J�) 34 ...... 2B 33 33 34 33 34 · ...... (321 33 2B (32) :: ... 32 34 FOV MO PSO SF CPSO 39 DB - ( 8.82 DB 4.84 DB P( 2Y. 1.57 DB 3.67 DB P 8.5Y.

"H II GHT: OUTSIO HORHAL L1ms 819 FP 816 5.8 FL 8119 FH APR 28115 28 2B 25 (U) 29 di) 31 29 (��) 24 38 31 31 2B 2B 38 38 <31)31 (31l !� 21 29 27 32 32 31 32 27 • � � • '" · · --.:..:.....::=--. 38 (a 31 3 3 134 33 32 (34)(W------·------34 (J5) 32l 32 J 32 38 : ...... : ( h 36 3 (n) . . : . . . . ::: 3 ...... 3 31 . :: ...... :::: ...... ( 3838) 3 33 32 (32)31 · ...... 32 34 31 38

SF CPSO FOV 110 PSO

- ( 2.7708 Pl 3S 08 1.85 DB 2.97 DB P lax 1.111 08 2Y.

85 GHT: OUTSIO NORMAL LIHITS 819 FP 8114 5.8 "" Fl 8119 FH HAY 28115 24 38 31 21 29 3l 38 29 2� 2B 32 (233 ) 32 33 (2 ) .. � . 38 � I 26 lB ,. (33) (1) (IB) .. 31 296 34 34 33 32 25 19 (8 • • ,. .. 33 (2938 ) lI3ll2) . :�� 32 (I 33 ) 38 32 ...... : :: >_:�:::.:: . . . . . : ...... :::. /;:: ...... : . : (I�) U . .:: . ::...... :::: ...... 32 . . 2 32 4 33 3 . :::: 3 (n) In) � 3� 33 33 34 33 2 (3 ) ( J 4) 32 32 31 38 PSO FOV "0 SF CPSO

- ( 2% ( 3B De 1.22 DB 4.47 De P 8.97 08 4.35 DB P 1.5Y.

8. (contd). For legend see 485. Fig. p. which has resulted in a mean lOP of 20 mmHg with Considerations related to blood flow (Table 5) virtually no diurnal variation. A clinical observation is Blood flow to the optic nerve can improve when lOP is 35 0 that patients may seem to improve following filtering lowered --4 (Fig. 7). When lOP is lowered, arterial flow will increase.35 This will occur regardless of the level of surgery performed because of progressive field loss due lOP because, whatever the baseline lOP before it was to glaucoma, despite no apparent change in the mean lowered, that baseline lOP was exerting some gradient of level of lOP following the surgery. pressure against which the blood entering the eye had to

483 26 5.1 MM OCT FP 115 21115 : :::::: :-0;:'0::" 28 31 25 25 .. 29 (��) 28 29 22 � 31 31 (n)31 31 12 \\l\UHi"\':lt:. 31 32 29 • • " .. (11) (31) (29) . . . . 33 21 32 34 31 38 21 21 23 ______. __,. _ __ _-;- __. _� • _ a -;- 32 33 35 34 32 32 (8 (I�) IU) 34 34 33 32 33 33 38 31 ...... : : :: : . . . : : :::: (31) ...... ::>�<>::::::::><>: . (33) . . .. : . :: . . ... : ...... : 31 31 32 31 . . . .. : . . . . : ...... : (J!) (It) ...... 3 34 31 8 ...... : : 2 3 . . CPSD FOV PSO SF ItO DB DB P 2r. DB • DB 3.24 DB P 5r. 35 8.66 ( 1.81 3.1lS (

23 CHT: OUTSIO NORMAL LIms 5.8 MM FL 1121 FN li9 FP 13 Al'R II 21115 : : 96 : : : : ::::::::: : : : ::: ::::::: :: :::::: 28 28 29 21

. . .. \�:.�:.::�:ll:l\ ll·\\····l�� (J� �: :it �� :�t: • ) ( l�) . . . . _ _ ...... ::::...... 31 25 32 34 33 32 21 25 11 _ ___ _ ··_· _· ______�_ . . �: �: _ _ :-- _ _ . _ :-- � ...... :.::: · ·.--01)(23) (21) ...... · 31 35 134 33 34 32 28 ::::::... . -.'.• ...... '...... :::::::: 2 33 (35) 34) - . : 2 33 3 : : : :: . : :: : ... '. . .. • ••••••... ::: 32 34 33 3 32 : :;. :-:-:- -:- . : : : ::::: : 4 - . : : :: - : (n ) : : : : 33 32 33 32 ' . : - : - : - :- : . : - : . . . . . (32)34 (��) (32) . . '. ' ...... 34 32 31 . . 38 CPSD FOV MD PSD Sf - ( 187. 1.45 DB 2.57 DB P < lX 38 08 8.1lS 08 3.88 DB P

5.1 11 CHT: BORDER IHE MM FL 18 FH liB FP liB II 21115 OCT ::. .: :::: 96 :: .: . :: : 26 24 29 21 :: �� >�:n��;r; :»::::.. 29 �1 28 29 33 28 �:�«� 32 32 31 32 • 32 (II) . "«« . _ . : l: . _ � :n: __ . _ _. . 32 34 31 38 ______. ______� (�§)� � ... .. ::.. :: ...... "':::::::::::"':"::; ) . -:' ' -: -:. :.: -:.:.:::::: 32 n 33 33 134 35 32 38 . 34 '· . ' : (I 34) .'- <.::: • . . . . . 3 · : : :';. . : ' : : :. : . :...... -: . . . 32 ( 345) 33 34 32 :- . .- . 32 3J (J�) - . :- - . : : ::::: : : . ) : : :. :. : : : : : : : 32 (J3 33 34 33 32 '.:.:-:-:.:.:.: ...... (32) (32) ...... 34 32 31 38 • ...... PSD SF CPSD FDV . ItO DB DB DB 1.89 DB P ( 34 DB :: + 8.36 2.48 1.58 187.

22 CHT: DUTSID HDRMAL LIM ITS 5.1 MM FL 1128 FH 1118 FP 1118 APR 21115 .. . . :: . 91 :: )::. :: :::- 24 24 29 . �h . :�\\\<;��;: � » �<� . ( ' 38 ( 16 ...... TYT�:...... :. .�� .:". (33)) (31) ,. • " " . . �: U . ' : (U) �� (n)�: .. :\yy«�: . . . : : : ':: :�: 32 31 28 (29) . : 29 ____ _ . . ______""_ . ___ . . : : : : �� ) 36 (�I) .E._ --,- _ _ • _ .,. • :::. : . :: . . . . : . . : . . : : : . . . . ' : : ...... :: .. :::: 38 (8 33 33 134 31 36 38 38 ...... : : . . . . .••...... : :: . . ..• : . : : . (32) (35) 3334) .- ::::: ::: :-:::: :::::::��;�::::::": 32 36 34 31 32 . : . (n) . · ...... • . ••. ..••.• ••. 33 � . . 33 32 (33�) 39 ...... '...... (31)32 (32) ...... ' ...... 32 34 31 38 FOV PSD SF CPSD ItO 31 - 1.45 08 3.29 DB P ( 5X DB 2.89 08 P D9 1.45 ( 2Z

8. (con/d). For legend see 485. Fig. p.

push. Thus, assuming that the blood pressure in the eye If any degree of insufficient nutrition to the neurones

in the arterioles entering the eye is X, and the lOP is Y, is present due to insufficient blood flow, then increasing the so-called perfusion pressure that will result in blood the perfusion pressure by decreasing lOP pressure will 5 7 56 entering the eye is X-y.3 ,3 , Regardless of the initial be theoretically of benefit to those neurones. Insufficient

level of Y, the lower Y becomes the greater the perfusion blood flow may be the result of disease within the blood pressure becomes. vessels, or inadequate nutrients within the blood itself.

484 : :

16 CHTI OUTSIO HORHAL LIHITS 5.8 HH FL li21 FH 1119 FP 11118 OCT 211115 97 ...... :::::::...... ::::::. .:::::::::...... :', 28 28 29 29 ...... : :::::: .: : ' , : : : : ::'.::', 33 29 313122 JI (33)(38) ::::::::: :::::: .::-::::: ..� .: .. (311 . .: 3 31 � . .. � . . . ::...... :�:::::: : :: :.:.:.:...... : ...... :.:�:�::::.:�::: :'. . 3831 258 (iI)34 3234 31 ( 32B )(�I)( nII ) 19 �. � - � ------: 23 .. -=.,.-- ...· -( ------:. : : : .:-:-:-:-:::-:::-:- 32 29) 35 134 33 (29)(7132 34 32 :-:-: - - - ' ' : "• :...... (B 33 ( 35 ) 34) ...... 32 32 (��) . 32 33 34 34 . . . . ( ) '.':'. :< .:.:. : . : : : . : : : . : . : : : 33 32 B35 : -: -: - : -: : : : : :: : ' : ' : ' ' : ' : ' : ' (��) 31 (��) . : . . : ...... ' . . • • • • • 32 32 33 34 � HD PSD SF FOV ; CPSD 36 08 ; + 8.B3 DB 4.82 08 ( 2r. 8.87 08 08 P ; P 3.91 ( 1.5Y. : 16 CHT:; [HE 5.8 HH : BORDER FP 2/12 APR FH 1110 : 211115 ...... : ::::" 98 28 :: ��: ��:;�:;.�� 26 29 2S :::: :: ::: : : :: . . 31 31 28 :: : ::: .:: . ::::::: : :: : : .: : : :: , 21 29 28 ::: :: :: :: : ' :::::: ::::' : . . . . (31) (29) 31 26 :.:.: .. :::::: . . . . :::::::::: : 38 32 31 34 31 31 . ..' . : , : : . . . :: . .. ::::::::::::"::" :" (29) (31) 25 21 . . . . . :. : : .: ...... '.: .'..::::: : .: :'.: :.. ::�::.::� 28 25 .. � . .. � . . . . . ' . 33 29 32 34 33 .. .. : . . . . 31 33 134 ) ...... ;;:;:::::: 33 (�� -3-8 -3-8 ------.,.------ .:. . . 16 33 (35) . . . . : 4) .. :: ...... ::::::: 3 : :::/.;:::::::. . 34 38 34 33 33 32 32 .. .: :: : ...... : ...... 33 ...... :...... (31) 32 (33)33 32 : : 32 33 33 : (32) (34) .. . 32 32 33 34 : : . PSO SF FOV : � HO CPSO DB + 8.16 08 DB ( 37 � 2.39 1.89 DB 2.118 08 P 18'1 � � . : CHTI � \: 5.1 HH " UmH" ORHAl L1ms 1119 FP 1118 ��;:��. : FL 211115 OCT ��::��::::. . �� 26 38 27 27 98 ...... : ...... �: :. 31 (�r) 28 27 (��) 38 :. 28 32 31 32 31 31 38 24

. . · · _ .. . ::::.. :: ...... · · ·:::::: :··: :·· :·· ) ) 34 27 25 21 ______. . _._. . ______. . _ : : : <_--{ n (�� (W 33 (U' ----, _ . .,.-- �_ . : ::;::.::::: :: :::::::::::;;��: 32 2 33 (��,% 33 32 38 38 ...... : : . : :'.' ...... 32 33 34 33 32 32 ...... 32 (33) 37 (33) • . 33 33 32 31 ...... 32 (3238 •••...... ) • . . . . . (34) FOV ...... 32 34 31 38 PSD SF CPSD HD 36 08 + 8.26 08 2.12 08 1.12 08 1.75 08

8. (contd). Repeated visual field examinations over a 5 year period documented a gradual, total disappearance of a dense defect in this woman Fig. with primary open-angle glaucoma, whose lOP was lowered by filtering surgery.

Blood flow may be inadequate due to inappropriate characteristic of some glaucomatous eyes, and a decrease regulation of vessel size and blood flow due to in this engorgement has been noted with a decrease in abnormalities of regulation, or local or systemic forces lOP. The cause for this may be direct compression of the O causing decrease in flOW.1 ,36 Several factors that may veins or distortion of the lamina causing compression of affect the adequacy of the vessel and consequently its the central retinal vein. autoregulation include: age, atherosclerosis, diabetes, What is the significance for patients of the fact that vascular diseases, systemic arterial hypertension or discs can improve in appearance and visual function hypotension, use of specific systemic medications, improve following 'resetting' lOP? Studies from different various cardiovascular diseases, and hormones.10,37,38,57 centres confirm the clinical impression of some Lowering lOP may or may not have a beneficial effect on practitioners that patients with glaucoma 6 --h6 the abnormality of regulation, but presumably could characteristically get worse. 3 But patients in whom an increase flow due to an increase in perfusion pressure. improvement is noted are more likely to do better - that Patients with venous-stasis-related lOP will is, remain stable or improve in function - regardless of 67 characteristically show a decrease in the venous stasis the amount of noted lowering of lOP. This suggests with lowering of lOP.58-62 Lowering lOP may possibly that using improvement as a measure of 'control' of improve the health of the neurones by decreasing the glaucoma may be more appropriate than using a concept resistance to the venous outflow of blood from the eye. such as target pressure.68,69 However, such a method of Engorgement of the veins in glaucoma is an established directing therapy demands use of methods that are

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