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									PRIMARY OPEN ANGLE
GLAUCOMA AND RELATED
CONDITIONS
PRIMARY OPEN ANGLE GLAUCOMA
As the name implies, it is a type of primary glaucoma,
where there is no obvious systemic or ocular cause
of rise in the intraocular pressure. It occurs in eyes
with open angle of the anterior chamber. Primary open
angle glaucoma (POAG) also known as chronic simple
glaucoma of adult onset and is typically characterised
by slowly progressive raised intraocular pressure
(>21 mmHg recorded on at least a few occasions)
associated with characteristic optic disc cupping and
specific visual field defects.
ETIOPATHOGENESIS
Etiopathogenesis of POAG is not known exactly.
Some of the known facts are as follows:
(A) Predisposing and risk factors. These include
the following:
1. Heredity. POAG has a polygenic inheritance. The
approximate risk of getting disease is 10% in the
siblings, and 4% in the offspring of patients with
POAG.
2. Age. The risk increases with increasing age. The
POAG is more commonly seen in elderly between
5th and 7th decades.
3. Race. POAG is significantly more common,
develops earlier and is more severe in black
people than in white.
4. Myopes are more predisposed than the normals.
5. Diabetics have a higher prevalence of POAG
than non-diabetics.
6. Cigarette smoking is also thought to increase its
risk.
7. High blood pressure is not the cause of rise in
IOP, however the prevalence of POAG is more in
hypertensives than the normotensives.
8. Thyrotoxicosis is also not the cause of rise in
IOP, but the prevalence of POAG is more in
patients suffering from Graves’ ophthalmic disease
than the normals.
(B) Pathogenesis of rise in IOP. It is certain that rise
in IOP occurs due to decrease in the aqueous outflow
facility due to increased resistance to aqueous
Fig. 9.7. Technique of trabeculotomy.
GLAUCOMA 215
outflow caused by age-related thickening and
sclerosis of the trabeculae and an absence of giant
vacuoles in the cells lining the canal of Schlemm.
However, the cause of these changes is uncertain.
(C) Corticosteroid responsiveness. Patients with
POAG and their offspring and sibilings are more likely
to respond to six weeks topical steroid therapy with a
significant rise of IOP.
INCIDENCE OF POAG
It varies in different populations. In general, it affects
about 1 in 100 of the general population (of either
sex) above the age of 40 years. It forms about onethird
cases of all glaucomas.
CLINICAL FEATURES
Symptoms
1. The disease is insidious and usually
asymptomatic, until it has caused a significant
loss of visual field. Therefore, periodic eye
examination is required after middle age.
2. Patients may experience mild headache and
eyeache.
3. Occasionally, an observant patient may notice a
defect in the visual field.
4. Reading and close work often present increasing
difficulties owing to accommodative failure due
to constant pressure on the ciliary muscle and its
nerve supply. Therefore, patients usually complain
of frequent changes in presbyopic glasses.
5. Patients develop delayed dark adaptation, a
disability which becomes increasingly disturbing
in the later stages.
Signs
I. Anterior segment signs. Ocular examination
including slit-lamp biomicroscopy may reveal normal
anterior segment. In late stages pupil reflex becomes
sluggish and cornea may show slight haze.
II. Intraocular pressure changes. In the initial stages
the IOP may not be raised permanently, but there is
an exaggeration of the normal diurnal variation.
Therefore, repeated observations of IOP (every 3-4
hour), for 24 hours is required during this stage
(Diurnal variation test). In most patients IOP falls
during the evening, contrary to what happens in
closed angle glaucoma. Patterns of diurnal variation
of IOP are shown in Fig. 9.8. A variation in IOP of
over 5 mm Hg (Schiotz) is suspicious and over 8 mm
of Hg is diagnostic of glaucoma. In later stages, IOP
is permanently raised above 21 mm of Hg and ranges
between 30 and 45 mm of Hg.
Fig. 9.8. Patterns of diurnal variations of IOP: A, normal
slight morning rise; B, morning rise seen in 20% cases of
POAG; C, afternoon rise seen in 25% cases of POAG;
D, biphasic variation seen in 55% cases of POAG.
216 Comprehensive OPHTHALMOLOGY
2. Thinning of neuroretinal rim which occurs in
advanced cases is seen as a crescentric shadow
adjacent to the disc margin.
3. Nasal shifting of retinal vessels which have the
appearance of being broken off at the margin is
an important sign (Bayonetting sign). When the
edges overhang, the course of the vessels as
they climb the sides of the cup is hidden.
4. Pulsations of the retinal arterioles may be seen
at the disc margin (a pathognomic sign of
glaucoma), when IOP is very high.
5. Lamellar dot sign the pores in the lamina cribrosa
are slit-shaped and are visible up to the margin
of the disc.
(c) Glaucomatous optic atrophy. As the damage
progresses, all the neural tissue of the disc is
destroyed and the optic nerve head appears white
and deeply excavated (Figs. 9.10 C&D).
Pathophysiology of disc changes. Both mechanical
and vascular factors play a role in the cupping of the
disc.
  Mechanical effect of raised IOP forces the lamina
cribrosa backwards and squeezes the nerve fibres
within its meshes to disturb axoplasmic flow.
  Vascular factors contribute in ischaemic atrophy
of the nerve fibres without corresponding increase
of supporting glial tissue. As a result, large
caverns or lacunae are formed (cavernous optic
atrophy).
IV. Visual field defects. Visual field defects usually
run parallel to the changes at the optic nerve head
and continue to progress if IOP is not controlled.
These can be described as early and late field defects.
Anatomical basis of field defects. For better
understanding of the actual field defects, it is
mandatory to have a knowledge of their anatomical
basis.
(A) Distribution of retinal nerve fibres (Fig. 9.11).
1. Fibres from nasal half of the retina come directly
to the optic disc as superior and inferior radiating
fibres (srf and irf).
2. Those from the macular area come horizontally as
papillomacular bundle (pmb).
3. Fibres from the temporal retina arch above and
below the macula and papillomacular bundle as
superior and inferior arcuate fibres with a
horizontal raphe in between (saf and iaf).
III. Optic disc changes. Optic disc changes, usually
observed on routine fundus examination, provide an
important clue for suspecting POAG. These are
typically progressive, asymmetric and present a
variety of characteristic clinical patterns. It is essential,
therefore, to record the appearance of the nerve head
in such a way that will accurately reveal subtle
glaucomatous changes over the course of follow-up
evaluation.
Examination techniques. Careful assessment of disc
changes can be made by direct ophthalmoscopy, slitlamp
biomicroscopy using a + 90D lens, Hruby lens
or Goldmann contact lens and indirect
ophthalmoscopy.
The recording and documentation techniques
include serial drawings, photography and
photogrammetry. Confocal scanning laser topography
(CSLT) i.e., Heidelberg retinal tomograph (HRT) is an
accurate and sensitive method for this purpose. Other
advanced imaging techniques include optical
coherence tomography (OCT) and scanning laser
polarimetry i.e., Nerve fibre analyser (NFA).
Glaucomatous changes in the optic disc can be
described as early changes, advanced changes and
glaucomatous optic atrophy. Figures 9.9A & B show
normal disc configuration.
(a) Early glaucomatous changes (Figs. 9.9C&D)
should be suspected to exist if fundus examination
reveals one or more of the following signs:
1. Vertically oval cup due to selective loss of
neural rim tissue in the inferior and superior
poles.
2. Asymmetry of the cups. A difference of more than
0.2 between two eyes is significant.
3. Large cup i.e., 0.6 or more (normal cup size is 0.3
to 0.4) may occur due to concentric expansion.
4. Splinter haemorrhages present on or near the
optic disc margin.
5. Pallor areas on the disc.
6. Atrophy of retinal nerve fibre layer which may
be seen with red free light.
(b) Advanced glaucomatous changes in the optic
disc (Figs. 9.10A&B):
1. Marked cupping (cup size 0.7 to 0.9), excavation
may even reach the disc margin, the sides are
steep and not shelving (c.f. deep physiological
cup).
GLAUCOMA 217
Fig. 9.9. Normal optic disc (A, Diagrammatic depiction; B, Fundus
photograph) and optic disc showing early glaucomatous
changes (C, Diagrammatic depiction; D, Fundus photograph).
B
A
D
C
(B) Arrangement of nerve fibres within optic nerve
head (Fig. 9.12): Those from the peripheral part of the
retina lie deep in the retina but occupy the most
peripheral (superficial) part of the optic disc. While
fibres originating closer to the nerve head lie
superficially in the retina and occupy a more central
(deep) portion of the disc.
The arcuate nerve fibres occupy the superior and
inferior temporal portions of optic nerve head and are
most sensitive to glaucomatous damage; accounting
for the early loss in the corresponding regions of the
visual field. Macular fibres are most resistant to the
glaucomatous damage and explain the retention of
the central vision till end.
218 Comprehensive OPHTHALMOLOGY
Fig. 9.10. Optic disc showing advanced glaucomatous changes (A,
diagramatic depiction; B, fundus photograph) and
glaucomotous optic atrophy (C, diagramatic depiction; D, fundus
photograph).
Progression of field defects. Visual field defects in
glaucoma are initially observed in Bjerrum’s area (10-
25 degree from fixation) and correlate with optic disc
changes. The natural history of the progressive
glaucomatous field loss, more or less, takes the
following sequence:
1. Isopter contraction. It refers to mild generalised
constriction of central as well as peripheral field.
It is the earliest visual field defect occurring in
A C
glaucoma. However, it is of limited diagnostic
value, as it may also occur in many other
conditions.
2. Baring of blind spot. It is also considered to be an
early glaucomatous change, but is very non-specific
and thus of limited diagnostic value. Baring of the
blind spot means exclusion of the blind spot from
the central field due to inward curve of the outer
boundary of 30° central field (Fig. 9.13A).
B D
GLAUCOMA 219
Fig. 9.11. Distribution of retinal nerve fibres.
Fig. 9.12. Arrangement of nerve fibres within
optic nerve head.
Fig. 9.13. Field defects in POAG: A, baring of blind spot; B,
superior paracentral scotoma; C, Seidel's scotoma; D,
Bjerru-m's scotoma; E, double arcuate scotoma and
Roenne's central nasal step.
3. Small wing-shaped paracentral scotoma (Fig.
9.13B). It is the earliest clinically significant field
defect. It may appear either below or above the
blind spot in Bjerrum's area (an arcuate area
extending above and below the blind spot to
between 10o and 20o of fixation point).
4. Seidel’s scotoma.With the passage of time
paracental scotoma joins the blind spot to form
a sickle shaped scotoma known as Seidel’s
scotoma (Fig. 9.13C).
5. Arcuate or Bjerrum’s scotoma. It is formed at a
later stage by the extension of Seidel’s scotoma
in an area either above or below the fixation point
to reach the horizontal line (Fig. 9.13D). Damage
to the adjacent fibres causes a peripheral
breakthrough.
6. Ring or double arcuate scotoma. It develops
when the two arcuate scotomas join together
(Fig. 9.13E).
7. Roenne's central nasal step. It is created when
the two arcuate scotomas run in different arcs
and meet to form a sharp right-angled defect at
the horizontal meridian (Fig. 9.13E).
220 Comprehensive OPHTHALMOLOGY
8. Peripheral field defects. These appear sometimes
at an early stage and sometimes only late in the
disease. The peripheral nasal step of Roenne's
results from unequal contraction of the peripheral
isopter.
9. Advanced glaucomatous field defects. The visual
field loss gradually spreads centrally as well as
peripherally, and eventually only a small island of
central vision (tubular vision) and an
accompanying temporal island are left. With the
continued damage, these islands of vision also
progressively diminish in size until the tiny central
island is totally extinguished. The temporal island
of the vision is more resistant and is lost in the
end leaving the patient with no light perception.
Diagnosis of glaucoma field defects on HFA single
field printout. Glaucomatous field defects should
always be interpreted in conjunction with clinical
features (IOP and optic disc changes). Further, before
final interpretation, the fields must be tested twice,
as there is often a significant improvement in the field
when plotted second time (because patients become
more familiar with the machine and test process).
Criteria to grade glaucomatous field defects. The
criteria to label early, moderate and severe
glaucomatous field defect from the HFA central 30-2
test, single printout is depicted in Table 9.2.
Note. For proper understanding of Table 9.2,
evaluation of the Humphrey single field printout
described on page 485 should be revised.
Ocular associations
POAG may sometimes be associated with high myopia,
Fuchs’ endothelial dystrophy, retinitis pigmentosa,
central retinal vein occlusion and primary retinal
detachment.
INVESTIGATIONS
1. Tonometry. Applanation tonometry should be
preferred over Schiotz tonometry (see page 479).
2. Diurnal variation test is especially useful in
detection of early cases (see page 215).
3. Gonioscopy. It reveals a wide open angle of
anterior chamber. Its primary importance in POAG
is to rule out other forms of glaucoma. For details
(see page 206 and 546).
4. Documentation of optic disc changes is of utmost
importance (see page 216).
5. Slit-lamp examination of anterior segment to
rule out causes of secondary open angle
glaucoma.
6. Perimetry to detect the visual field defects.
7. Nerve fibre layer analyzer (NFLA) is a recently
introduced device which helps in detecting the
Table 9.2: Criteria to diagnose early, moderate and severe glaucomatous
field defects from HFA: 30-2- test.
Sr. Parameter Criteria for glaucomatous field defects
no. Early defects Moderate defects Severe defects
1. Mean deviation (MD) <– 6 dB – 6dB – 12 dB > – 12dB
2. Corrected pattern Depressed to the p<5% Depressed to the p <5%
Depressed to the p<5%
standard deviation
(CPSD)
3. Pattern deviation plot
   Points depressed < 18 (25%) < 37 (50%) > 37 (>50%)
below the p < 5%
or
   Points depressed < 10 < 20 > 20
below the p < 1%
4. Glaucoma Hemifield Outside normal limits Outside normal limits Outside
normal limits
Test (GHT)
5. Sensitivity in central No point < 15dB One hemifield may have Both
hemifield have
5 degree point with sensitivity points with sensitivity
<15dB <15dB
No point has 0 dB Any point has 0 dB
GLAUCOMA 221
glaucomatous damage to the retinal nerve fibres
before the appearance of actual visual field
changes and/or optic disc changes.
8. Provocative tests are required in border-line cases.
The test commonly performed is water drinking
test. Other provocative tests not frequently
performed include combined water drinking and
tonography, bulbar pressure test, prescoline test
and caffeine test.
Water drinking test. It is based on the theory that
glaucomatous eyes have a greater response to water
drinking. In it after an 8 hours fast, baseline IOP is
noted and the patient is asked to drink one litre of
water, following which IOP is noted every 15 min. for
1 hour. The maximum rise in IOP occurs in 15-30 min.
and returns to baseline level after 60 minutes in both
normal and the glaucomatous eyes. A rise of 8 mm of
Hg or more is said to be diagnostic of POAG.
DIAGNOSIS
Depending upon the level of intraocular pressure
(IOP), glaucomatous cupping of the optic disc and
the visual field changes (Fig. 9.14) the patients are
assigned to one of the following diagnostic entities:
1. Primary open angle glaucoma (POAG).
Characterstically POAG is labelled when raised IOP
(>21 mm of Hg) is associated with definite
glaucomatous optic disc cupping and visual field
changes.
However, patients with raised IOP and either typical
field defects or disc changes are also labelled as
having POAG.
2. Ocular hypertension or glaucoma suspect. Either
of these terms is used when a patient has an IOP
constantly more than 21 mm of Hg but no optic disc
or visual field changes (for details see page 224).
3. Normal tension glaucoma (NTG) or low tension
glaucoma (LTG) is diagnosed when typical
glaucomatous disc cupping with or without visual
field changes is associated with an intraocular
pressure constantly below 21 mm of Hg (For details
see page 224).
MANAGEMENT
General considerations
Baseline evaluation and grading of severity of
glaucoma. The aim of treatment is to lower intraocular
pressure to a level where (further) visual loss does
not occur. The management thus requires careful and
regular periodic supervision by an ophthalmologist.
Therefore, it is important to perform a good baseline
examination with which future progress can be
compared. The initial data should include: visual
acuity, slit-lamp examination of anterior segment,
tonometry (preferably with applanation tonometer);
optic disc evaluation (preferably with fundus
photography), gonioscopy and visual field charting.
American Academy of Ophthalmology (AAO)
grades severity of glaucoma damage into mild,
moderate and severe (Table 9.3).
Table 9.3: Severity of glaucoma damage
Degree Description
Mild Characteristic optic-nerve abnormalities
are consistent with glaucoma but with
normal visual field.
Moderate Visual-field abnormalities in one hemi-field
and not within 5 degrees of fixation.
Severe Visual-field abnormalities in both
hemifields and within 5 degrees of fixation.
Source : AAO 2000a
Fig. 9.14. Triad of abnormalities in disc, field and
intraocular pressure (IOP) for the diagnosis of glaucoma.
222 Comprehensive OPHTHALMOLOGY
Therapeutic choices include:
  Medical therapy,
  Argon or diode laser trabeculoplasty, and
  Filteration surgery.
A. Medical therapy
The initial therapy of POAG is still medical, with
surgery as the last resort.
Antiglaucoma drugs available are described in detail
on pages 423-427.
Basic principles of medical therapy of POAG
1. Identification of target pressure. From the baseline
evaluation data a ‘target pressure’ (below which
glaucomatous damage is not likely to progress)
should be identified for each patient. The target
pressure is identified taking into account the
severity of existing damage, the level of IOP, age,
and general health of the patient. Although it is
not possible to predict the safe level of IOP,
however, progression is uncommon if IOP is
maintained at less than 16 to 18 mm of Hg in
patients having mild to maderate damage. Lower
target pressures (12-14 mmHg) are required in
patients with severe damage.
2. Single drug therapy. One topically instilled
antiglaucoma drug should be chosen after due
consideration to the patient’s personal and
medical factors. If the initial drug chosen is
ineffective or intolerable, it should be replaced by
the drug of second choice.
3. Combination therapy. If one drug is not sufficient
to control IOP then a combination therapy with
two or more drugs should be tried.
4. Monitoring of therapy by disc changes and field
changes and tonometry is most essential on
regular follow-up. In the event of progress of
glaucomatous damage the target pressure is reset
at a lower level.
Treatment regimes. There are no clear-cut
prescribed treatment regimens for medical therapy of
POAG. However, at present considerations are as
follows :
I. Single drug therapy
1. Topical beta-blockers are being recommended as
the first drug of choice for medical therapy of POAG
in poors and average income patients. These lower
IOP by reducing the aqueous secretion due to their
effect on beta - receptors in the ciliary processes.
Preparations. In terms of effectiveness, there is little
difference between various beta-blockers. However,
each offers a slight advantage over the other, which
may help in choosing the particular medication as
follows:
  Timolol maleate (0.25, 0.5% : 1-2 times/day) is
most popular as initial therapy. However, it should
not be used in patients having associated
bronchial asthma and/or heart blocks.
  Betaxolol (0.25% : 2 times/day). Being a selective
beta-1 blocker it is preferred as initial therapy in
patients with cardiopulmonary problems.
  Levobunolol (0.25, 0.5% : 1-2 times/day). Its action
lasts the longest and so is more reliable for once
a day use than timolol.
  Carteolol (1%: 1-2 times/day). It raises
triglycerides and lowers high density lipoproteins
the least. Therefore, it is the best choice in
patients with POAG having associated
hyperlipidemias or atherosclerotic cardiovascular
disease.
2. Pilocarpine (1, 2, 4%: 3-4 times/day). It is a very
effective drug and had remained as the sheet anchor
in the medical management of POAG for a long time.
However, presently it is not being preferred as the
first drug of choice or even as second choice. It is
because of the fact that in younger patients it causes
problems due to spasm of accommodation and miosis.
Most, but not all, older patients tolerate pilocarpine
very well; however, axial lenticular opacities when
present precludes its use in many such patients.
Therefore, presently pilocarpine is being considered
only as an adjunctive therapy where other
combinations fail and as second choice in poor
patients.
Mechanism of action. Pilocarpine contracts
longitudinal muscle of ciliary body and opens spaces
in trabecular meshwork, thereby mechanically
increasing aqueous outflow.
3. Latanoprost (0.005%: once daily). It is a
prostaglandin by nature and decreases the IOP by
increasing the uveo-scleral outflow of aqueous.
Presently, it is being considered the drug of first choice
for the treatment of POAG (provided patient can
afford to buy it). Therefore, it is a very good
GLAUCOMA 223
adjunctive drug to beta-blockers, dorzolamide and
even pilocarpine when additional therapy is indicated.
4. Dorzolamide (2%: 2-3 times/day). It is a recently
introduced topical carbonic anhydrase inhibitor which
lowers IOP by decreasing aqueous secretion. It has
replaced pilocarpine as the second line of drug and
even as an adjunct drug.
5. Adrenergic drugs. Role in POAG is as follows:
i. Epinephrine hydrochloride (0.5, 1, 2%: 1-2 times/
day) and dipivefrine hydrochloride (0.1%: 1-2
times/day). These drugs lower the IOP by
increasing aqueous outflow by stimulating beta
recepters in the aqueous outflow system. These
are characterized by a high allergic reaction rate.
Their long-term use has also been recognized as
a risk factor for failure of filtration glaucoma
surgery. For these reasons, epinephrine
compounds are no longer being used as first line
or second line drug. However, dipivefrine may be
combined with beta-blockers in patients where
other drugs are contraindi-cated.
ii. Brimonidine (0.2% : 2 times/day). It is a selective
alpha-2-adrenergic agonist and lowers IOP by
decreasing aqueous production. Because of
increased allergic reactions and tachyphylaxis
rates it is not considered the drug of first choice
in POAG. It is used as second drug of choice and
also for combination therapy with other drugs.
II. Combination topical therapy
If one drug is not effective, then a combination of
two drugs—one drug which decreases aqueous
production (timolol or other betablocker, or
brimonidine or dorzolamide) and other drug which
increase aqueous outflow (latanoprost or brimonidine
or pilocarpine) may be used.
III. Role of oral carbonic anhydrase inhibitors in
POAG
Acetazolamide and methazolamide are not
recommended for long-term use because of their sideeffects.
However, these may be added to control IOP
for short term.
B. Argon or diode laser trabeculoplasty (ALT or
DLT)
It should be considered in patients where IOP is
uncontrolled despite maximal tolerated medical
therapy. It can also be considered as primary therapy
where there is non-compliance to medical therapy.
Technique and role of ALT in POAG. It has an
additive effect to medical therapy. Its hypotensive
effect is caused by increasing outflow facility,
possibly by producing collagen shrinkage on the
inner aspect of the trabecular meshwork and opening
the intratrabecular spaces. It has been shown to lower
IOP by 8-10 mm of Hg in patients on medical therapy
and by 12-16 mm in patients who are not receiving
medical treatment.
The treatment regime usually employed consists
of 50 spots on the anterior half of the trabecular
meshwork over 180°.
Complications. These include transient acute rise of
IOP, which can be prevented by pretreatment with
pilocarpine and/or acetazolamide; and inflammation
which can be lessened by use of topical steroids for
3-4 days. Less commonly haemorrhage, uveitis,
peripheral anterior synechiae and reduced
accommodation may occur.
C. Surgical therapy
Indications
1. Uncontrolled glaucoma despite maximal medical
therapy and laser trabeculoplasty.
2. Non-compliance of medical therapy and nonavailability
of ALT.
3. Failure with medical therapy and unsuitable for
ALT either due to lack of cooperation or inability
to visualize the trabeculum.
4. Eyes with advanced disease i.e., having very
high IOP, advanced cupping and advanced field
loss should be treated with filtration surgery as
primary line of management.
5. Recently, some workers are even recommending
surgery as primary line of treatment in all cases.
Types of surgery
Surgical treatment of POAG primarily consists of a
fistulizing (filtration) surgery which provides a new
channel for aqueous outflow and successfully
controls the IOP (below 21 mm of Hg).
Trabeculectomy is the most frequently performed
filtration surgery now-a-days. The details of filtration
operations are described on page 237.

								
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