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of this issues content relates to tonometry and intraocular pressure
(IOP), a topic we once thought we understood. Yes, a test and its outcome
we long took for granted is now being questioned. Thinking about Goldmann
tonometry and its changing perception led me to reflect back on my Optometry
school days. I went to the New England College of Optometry in Boston
where the general clinic was located in a restored building in Kenmore
Square. The building was long and narrow with examination rooms found
at the ends of the building, connected by corridors. It may seem strange
now but at the time, not all the slit lamps had Goldmann tonometers.
Thus the student would have to move their patient during the examination
to the corridor where a slit lamp with a Goldmann tonometer as well
as a noncontact tonometer was available. The student could choose which
test to perform but the Goldmann tonometer was almost always utilized.
The noncontact tonometers measurements were perceived as estimates
while the Goldmann tonometer was seen as a precise Swiss instrument.
The sentiment was that if the mires were sized appropriately and the
rings adjusted properly, IOP measured by Goldmann reflected the pressure
within the eye.
I first became aware of concerns regarding the accuracy of Goldmann
readings just after refractive surgery became commonplace. Reports surfaced
that IOP reduction was being seen after the procedure, questioning some
basic tenets around which the procedure was based. We now recognize
that several corneal biomechanical factors such as thickness, rigidity,
curvature and hydration may affect IOP measurements. In this issue several
authors report on these topics and describe some of the newer tonometric
instrumentation. After approximately 50 years with little improvement
in the equipment used to measure IOP, we are now seeing major changes.
The outcomes should lead to improvements in how we take care of patients
with glaucoma, though it will take years before we become comfortable
in using the new set of measurements.
Murray Fingeret, OD
President, Optometric Glaucoma Society
Changing Role of Intraocular Pressure in Glaucoma
It is with pleasure I write this editorial in Pauls absence. Given
this is the final issue of this journal for this year, let me begin by
wishing you all a very festive holiday season from the editorial board.
There was a time when glaucoma was defined as an IOP >21 mmHg. So what
is the role of IOP within the context of the modern glaucoma clinic?
First of all, can IOP be measured reliably given that corneal curvature
and thickness can influence the forces required for applanation? It would
appear that although these issues are being addressed by considerable
research, which attempts to quantify the relationship between IOP, corneal
curvature and thickness, a consensus on this relationship and the potential
impact of other biomechanical factors, has yet to be reached. This begs
the question: how important is IOP to glaucoma? More specifically, is
there any evidence to support the dogma that glaucoma is a disease caused
by an IOP imbalance which damages axons by some, as yet, unknown mechanism?
Right now we need to differentiate the role that IOP has as a diagnostic
indicator from the benefit of lowering IOP in glaucoma management. Lowering
IOP is well recognised as an effective treatment to slow loss of vision
in glaucoma suspects (OHTS), cases of early glaucoma (EMGT) and cases
of advanced disease (AGIS). The problem of "treating" IOP is
that we can run into the danger of becoming transfixed by the number
(target pressure) and not by its significance to the patient. It is the
balance between IOP and blood pressure (ocular perfusion pressure) that
is important in sustaining the optic nerve.
IOP can vary diurnally as does blood pressure. The unfortunate thing is
that in some patients, as IOP peaks in the early morning, blood pressure
reaches its trough, reducing ocular perfusion pressure. It is these variations
that are often unseen by the clinician who measures IOP (and/or BP) during
office hours. More importantly, do we know how blood pressure medications
taken by the patient impact on this relationship, or the effect that short-term
transient perfusion pressure troughs (IOP spikes and/or blood pressure
dips) have in compromising the optic nerve? In this edition some of these
issues will be canvassed to give a modern slant to the IOP story.
Algis J. Vingrys, BScOptom, PhD
IDEAS AND PAPERS
Does an IOP spike affect
Despite the well-known association between IOP and glaucoma little is
known about how short duration changes in IOP ("spikes") affect
retinal integrity. Recent research from our laboratory (1) has considered
this problem in rats (n=6-7 per group) by cannulating the anterior chamber
and elevating IOP to 50 or 70 mmHg for periods of 15-60 minutes. Retinal
integrity was quantified by measuring the retinal response to full-field
flashes of light (i.e. the electroretinogram, ERG) and quantified in
terms of specific ERG components known to reflect function of outer
retinal (photoreceptor, P3), middle retinal (ON-bipolar cell, P2) and
ganglion cell (scotopic threshold response, STR) layers. We assessed
both the loss of function and how quickly function recovered from a
given IOP challenge.
We found that 50 mmHg spikes (35 mmHg above baseline for 42 minutes)
particularly compromised ganglion cell responses (STR 80 +/- 7%
reduction), leaving outer retinal responses largely unaffected (P2,
33 +/- 11% and P3, 6 +/- 6% reduction). Not only was ganglion
cell function more compromised during the insult, but it also took longer
to recover after IOP normalisation, requiring 22 minutes to return to
50% of the original amplitude (versus 2-5 minutes for P2 and P3).
Our work has shown that both duration and peak IOP influence the function
of retinal neurons. IOP spikes having a common integral (pressure x
duration) did not result in the same level of dysfunction. In fact higher
pressures produced greater ganglion cell functional loss (70 mmHg 100
+/- 1% vs 50 mmHg 80 +/- 7% reduction) and slower recovery.
Thus, for insults having the same IOP integral, the peak IOP is the
principal determinant of functional loss and recovery. This suggests
that IOP fluctuations should be minimised in patients.
We also found that as the duration of insult was prolonged for a given
IOP (70 mmHg), ganglion cell function took progressively longer to recover.
In fact this relationship was linear. Taken together, these results
suggest that treatment aimed at retaining ganglion cell integrity should
not only attempt to reduce the "mean" IOP level, but also
to limit IOP fluctuation.
Bang V Bui, Zheng He and Algis J Vingrys,
Department of Optometry & Vision Sciences
University of Melbourne, Victoria, 3010, Australia
1. Zheng He, Bang V Bui, Algis J Vingrys (2006). The rate of functional
recovery from acute IOP recovery. Invest Ophthalmol Vis Sci.;47:4872-4880.
How should we best measure and react to spikes: IOP and the number
of papers written about CCT
As interest swells over the effect that central corneal thickness (CCT)
may have on the relative risk of glaucoma progression, much related
research activity appears to be focused on the specific influence that
CCT may have on the apparent intraocular pressure (IOP) measured by
one tonometer or another. The fundamental problem here is that the current
"gold-standard" method of tonometry, namely Goldmann Applanation
Tonometry (GAT), is based on an inherent assumption that CCT is 520
microns, yet there is a wide variation in CCT across the population,
which introduces qualitatively predictable error in the relationship
between the measured (GAT) and the true IOP (i.e. manometrically measured).
This problem has driven efforts to develop alternative methods of tonometry,
such as Dynamic Contour Tonometry discussed elsewhere in this issue.
One such method, generally known as "rebound" or "impact"
tonometry, has been further developed into a new commercially available
device called the ICare "induction-based" impact tonometer
(Tiolat Oy, Helsinki, Finland). In a recent study , Brusini and colleagues
proposed "to compare the IOP readings taken with the new ICare
tonometer and with the GAT and to evaluate the influence of central
corneal thickness (CCT) on the IOP measurements." They concluded
that "a CCT change of 10 mum resulted in an ICare reading deviation
of 0.7 mm Hg" and further, that "[ICare] measurements
seemed to be influenced by CCT variations, and thus pachymetry should
always be taken into consideration." It is crucial to point
out that the authors are referring to the "deviation" from
what they assume to be the true IOP, the GAT value "corrected"
by the measured CCT according to a published formula . Notwithstanding
the circular logic of using CCT to calculate this "deviation"
and then attempting to "evaluate the influence of central corneal
thickness (CCT)", one of the most interesting findings from
this study (which the reader will not see addressed in the Discussion
section) is that the ICare tonometer appears to have an even larger
error than GAT for corneas that are progressively thinner or thicker
than average! For example, if one removes the CCT correction, and recalculates
the "deviation" (of ICare IOP from measured GAT IOP),
the linear function still has a positive slope of 0.2 mm Hg per 10 microns
of CCT difference. Thus, if GAT underestimates IOP by 2 mm Hg in an
eye with a relatively thin CCT of 495 microns , ICare further underestimates
IOP by an additional 1.5 mm Hg! The essential conclusions of this paper
are worthy of consideration, however, they are valid only if the true
IOP can be estimated from GAT using a simple linear correction factor
based on CCT. As we are learning, this is highly improbable.
Perhaps even more important than deriving an estimate for IOP "correction"
is the need to develop better methods of 24-hour IOP monitoring. Firstly,
glaucoma diagnosis should depend more on evaluation of optic disc structure,
retinal nerve fiber layer integrity, and visual function anyway, rather
than on IOP per se. Secondly, corneal biomechanical properties
(and their effect on IOP estimates) are unlikely to change substantially
throughout most patients lives, and we can use a consistent method
of tonometry to assess the reduction of IOP over time brought about
by therapy. The more important challenge may well be that significant
IOP elevation commonly occurs outside of typical office hours, and we
do not currently have any satisfactory way to monitor this. A recent
study by Barkana et al  adds further evidence, and eloquent
argument, to support this important point. They report on 32 patients
that had been admitted to the hospital for 24-hour IOP monitoring. Four
important findings were 1) the 24-hour peak IOP was 2 mm Hg higher,
on average, than the "office IOP peak" (obtained between 7
am and 4:30 pm); 2) the difference between the 24-hour peak and the
office IOP peak was at least 2 mm Hg in over 40% of eyes, and over
4 mm Hg in 19% of eyes; 3) the peak IOP was recorded outside
of office hours in 69% of patients; 4) IOP fluctuation (peak minus
trough) was 3 mm Hg larger over the 24-hour period than during office
Unlikely to be stated more clearly in paraphrase, their concluding argument
is quoted here in full: "...our data suggest that in glaucoma patients
with advanced disease or with progression that is disproportionate to
known IOP measurements, 24-hour IOP monitoring can reveal higher peaks
and wider fluctuation of IOP than those found during typical office
hours, measured either in multiple office visits or repeatedly during
a single day. In these patients, 24-hour IOP monitoring may suggest
a greater role for IOP-related risk for glaucoma progression than previously
suspected and thus may justify a more aggressive IOP-lowering treatment
strategy. Until accurate self-tonometry devices become widely available,
or until a method is found to accurately predict the 24-hour peak and
range of IOP in individual patients, we suggest that clinicians consider
obtaining 24-hour IOP measurements for selected patients."
Brad Fortune, OD, PhD
1. Brusini P, Salvetat ML, Zeppieri M, Tosoni C, Parisi L. Comparison
of ICare tonometer with Goldmann applanation tonometer in glaucoma patients.
J Glaucoma. 2006;15:213-217.
2. Doughty MJ, Zaman ML. Human corneal thickness and its impact on intraocular
pressure measures: a review and meta-analysis approach. Surv Ophthalmol.
3. Barkana Y, Anis S, Liebmann J, Tello C, Ritch R. Clinical utility
of intraocular pressure monitoring outside of normal office hours in
patients with glaucoma. Arch Ophthalmol. 2006 Jun;124(6):793-7.
PASCAL®, Dynamic contour tonometer (DCT) is a novel measuring device
using the principle of contour matching instead of applanation to eliminate
the systematic errors inherent in previous tonometers. These factors include
the influence of corneal thickness, rigidity, curvature, and elastic properties.
In Vivo Cannulation
Study (A. Weber, A.G. Boehm, E. Spoerl, L.E. Pillunat)
The yellow curve is the manometric reference line (true IOP).
The blue curve is the reported IOP from the PASCAL®. When
the PASCAL is on the cornea, the two curves are almost identical.
Although this device is similar in appearance to a Goldmann, it does not
work like Goldmann applanation tonometry (GAT): it neither applies a variable
force nor applanates the cornea. The device developed by Hartmut Kanngiesser
PhD, a Swiss research engineer was approved by the FDA in November 2003.
PASCAL DCT uses a miniature piezoelectric pressure sensor embedded within
the tonometer tip that is contour-matched to the shape of the cornea.
The tonometer tip rests on the cornea with a constant appositional force
of one gram. This is an important difference from all forms of applanation
tonometry in which the probe force is variable. When the sensor is subjected
to a change in pressure, the electrical resistance is altered and the
PASCAL's computer calculates a pressure change in concordance with the
change in resistance. The contour matched tip has a concave surface of
radius 10.5 mm, which approximates the corneas shape when the pressure
on both sides of it are equal. This is the key to the PASCALs ability
to neutralize the effect of intra-individual variation in corneal properties.
process of scientific validation thus far has been three pronged; the
initial task was to explain the inherent weaknesses of applanation and
the second to demonstrate the DCTs adherence to true manometric IOP. The
third, and perhaps most daunting, was to demonstrate how relevant these
differences are to the practicing clinician in the day-to-day diagnosis
and management of glaucoma.
At The University
of Dresden, Germany, Andreas Boehm, MD performs PASCAL IOP measurement
while a cannula is in the anterior chamber for pressure control
and reference measurement.
Initial studies with in vitro cannulation and manometric comparison (1)
and pre and post operative LASIK comparisons (2) established a foundation,
but left open the ultimate question of in-vivo validation. Meanwhile,
approximately 3 dozen papers and posters (GAT - DCT comparisons) have
been presented which corroborate that the PASCAL accurately determines
IOP without being influenced by individual variation in corneal properties.
The conclusion drawn from these investigations has been that central corneal
thickness (CCT) has little influence on DCT outcomes. Comparing DCT IOP
measurements to different IOP corrective algorithms such as the Ehlers
formula varies widely, raising the question which is most accurate, the
DCT or GAT with "correction"?
Boehm et al, at The University of Dresden performed in vivo cannulation
on 49 eyes with the PASCAL DCT and demonstrated its ability to closely
adhere to true manometric IOP independent of intra-individual variation
in corneal properties. Their results were presented at ARVO 2006. Also
presented at the 2006 ARVO meeting were the results from the Los Angeles
Latino Eye Study (LALES) (Varma et al) which found that DCT IOP
was relatively uninfluenced by CCT in approximately 4000 eyes. Perhaps
of greater interest was the observation that DCT was as much as 6mm Hg
higher than Goldmann in approximately 2.5% of eyes, suggesting that,
given the assumption that DCT is closest to manometric IOP, these individuals
might be prone to delayed glaucoma diagnosis with Goldmann tonometry.
A comprehensive list of published literature (peer reviewed and otherwise)
can be found at the Zeimer website: www.pascal-tonometer.com.
Elliot M. Kirstein, OD, FAAO
1. Kniestedt C, Nee M, Stamper RL (2004). Dynamic contour tonometry:
a comparative study on human cadaver eyes. Arch Ophthalmol. 2004; 122(9):
2. Kaufmann C, Bachmann LM, Thiel MA (2003). Intraocular pressure
measurements using dynamic contour tonometry after laser in situ keratomileusis.
Invest Ophthalmol Vis Sci;4 4(9):3790-4.
Introduction to the Ocular Response Analyzer (ORA)
biomechanical properties influence the results of different ocular measurements
and procedures, affecting diagnosis and management of ocular diseases.
Until now, assessing in vivo biomechanical properties of corneal tissue
has not been possible. Corneal measurements have been confined solely
to geometry such as thickness and topography.
The Ocular Response Analyzer (Figure A) applies force to the cornea via
a collimated air pulse, with an electro-optical system used to monitor
corneal curvature. The cornea moves inwards with the air pulse going past
applanation before finally returning to normal curvature. The curvature
detection system records two pressure values at inward and outward applanation
events. Corneal viscous effects create damping that manifests itself as
a difference between the two pressures. Averaging these two pressures
provides a Goldmann-correlated IOP (IOPG). The difference between these
two pressure values defines corneal hysteresis (CH) (Figure B). CH is
the first in-vivo measurement of corneal biomechanical properties. It
is not strongly correlated with other known ocular measurements, including
IOP and central corneal thickness (CCT).
Clinical studies have shown that CH can be used to identify conditions
such as keratoconus and Fuchs dystrophy (1-3). Because CH measurements
decrease significantly after refractive surgery, low CH is considered
to be a contraindication for refractive surgery related to risk of developing
post-LASIK ectasia (1). As such, clinical applications of the ORA in corneal
and refractive disciplines are fairly obvious.
ORA and Glaucoma
Recent studies, including the Ocular Hypertension Treatment Study (OHTS),
have suggested that low CCT is an independent risk factor for development
of glaucoma. Some investigators have theorized that corneal properties
may reflect overall ocular tissue characteristics, and thereby provide
new information that will aid in diagnosis and management of glaucoma.
Studies utilizing the Ocular Response Analyzer have supported this hypothesis.
Compared to normals, glaucomatous subjects have a less than average CH
and a much wider range. A recent study has suggested that CH may also
be an indicator of glaucoma progression, independent of IOP, CCT, and
other factors (4).
Goldmann applanation tonometry (GAT) was designed to provide accurate
measurements in eyes with "average" corneas but corneas vary
more than previously thought. It is clear however, that corneal influence
on GAT cannot be accounted for solely by differences in CCT. In fact,
"correcting" IOP based on CCT can lead not only to improper
magnitude, but also to an incorrect direction sense of the adjustment.
Corneal models indicate that biomechanical factors are of substantially
greater significance than CCT (5).
ORA bi-directional applanation provides a basis for corneal-compensated
intraocular pressure (IOPcc), that takes into consideration biomechanical
properties. IOPcc appears significantly less affected by corneal properties
than GAT and other methods of tonometry. IOPcc has insignificant correlation
with CCT in normal eyes and stays relatively constant post-LASIK (6).
ORAs unique ability to provide a Goldmann-correlated IOP measurement
(IOPG) and IOPcc provides clinicians with an understanding of their difference.
This understanding, coupled with CH, provides a powerful combination of
tools to assist diagnosis and management of glaucoma.
David A. Luce, PhD
David A. Taylor,
Reichert Ophthalmic Instruments
1. Luce DA. Determining in vivo biomechanical properties of the
cornea with an ocular response analyzer. J Cataract Refract Surg 2005;31:156
2. Change in Axial Length Following Surgical Decompression. A Surrogate
for the Material Properties of the Eye Wall (2006). S.A. Tanimoto, L.A.S.
Mello, Jr., J.D. Brandt. ARVO abstract No 4423.
3. IOP and Corneal Biomechanical Metrics in Eyes With Keratoconus and
Fuchs' Dystrophy Compared to Pachymetry-Matched Controls (2006). J.P.
Sanderson, M.A. Qazi, C.J. Roberts, J.S. Pepose. ARVO abstract no 2267.
4. Congdon NG, Broman AT, Bandeen-Roche K, Grover D, Quigley HA (2006).
Central corneal thickness and corneal hysteresis are associated with glaucoma
damage. Am J Ophthalmol; 141(5): 868-75.
5. Liu J, Roberts CJ. Influence of corneal biomechanical properties on
intraocular pressure measurement: quantitative analysis. J Cataract Refract
6. Medeiros FA and Weinreb RN (2006). Evaluation of the Influence of Corneal
Biomechanical Properties on Intraocular Pressure Measurements Using the
Ocular Response Analyzer. J Glaucoma; 15: 364-370
A 75 year old white man
presented with a complaint of gradually worsening blurred vision in
his left eye first noticed 6 to 7 weeks prior to the examination. He
had not experienced ocular pain, haloes around lights or headache. He
had no history of ocular disease or trauma and was not taking any ocular
medications. He was on therapy for systemic hypertension, atrial fibrillation
and raised cholesterol (warfarin, simvastatin, digoxin and lisinopril.)
He did not report any known family history of glaucoma or blindness.
Visual acuities were OD 20/30 and OS 20/60, improving to 20/40 with
pinhole. For his initial field tests a 24-2 SITA-Fast test was performed.
This fast thresholding algorithm is less desirable than SITA Standard
which has the more desirable characteristics of both higher threshold
estimation validity and greater levels of reproducibility that are advantageous
for detection of defect progression. We use SITA-fast as a learning
test and preliminary result although in this case both eyes results
appeared reliable according to the indices. There was some evidence
of loss of corneal reflex on gaze tracking of the right eye, evidenced
by downward deflections of the plot, suggesting either drooping upper
eyelid or backward head movement. Losses of central fixation, represented
by upward deflections, were minimal. The right test (Figure 1a) shows
evidence of mild diffuse loss, indicated by a significantly reduced
mean deviation (MD) and widespread mild but significant reductions in
threshold sensitivity on the total deviation and its corresponding probability
plot. There was not definite focal loss, although a cluster of possible
shallow depressed locations were present in the superior paracentral
area, in addition to a likely temporal edge artefact. The result for
the left eye (Figure 1b) showed marked, significant diffuse depression
(MD -11.13dB). There was also significant focal losses present in the
inferior arcuate and paracentral areas visible on the pattern deviation.
PSD also highlighting irregularities of the field surface, consistent
with glaucomatous losses. The superior hemifield showed a probable nasal
Examination of the anterior segment revealed normal corneas with deep
quiet anterior chambers. Bluish-white translucent material was present
around both pupil margins although the pigmentary collarettes and other
areas of the irides appeared normal. There was no phacodonesis when
the patient was asked to make small lateral eye movements.
Intraocular pressure (IOP) was elevated bilaterally at OD 32 and OS
45mmHg by Goldmann applanation tonometry. Central corneal thickness
was OD 484 and OS 474µm. Gonioscopy revealed Shaffer grade 4 angles
OU through 360degrees, although there was variable degrees of trabecular
pigment present, greatest bilaterally in the inferior quadrants.
After pupil dilation, further bluish white material was visible on the
anterior surface of the crystalline lens, in a target-type pattern of
concentric circles (Figure 2). Crystalline lenses appeared centrally
positioned and had nuclear sclerotic lens opacities, OD trace level
and OS moderate.
Examination of the posterior segment demonstrated small vertical optic
nerve head diameters of 1.6mm in height OU, measured at the slit-lamp
beam. There was asymmetry in vertical cup-to-disc ratio OD 0.20 and
OS 0.50. Excavation was shallow, with the cups exhibiting a saucer-shaped
profile, making accurate identification of the cup edge difficult.
Figure 2. This
figure shows pseudoexfoliative material on the anterior capsule
surface, with arrows 1 and 2 showing the inner and outer boundaries
respectively of the region where this material has been rubbed
away by pupil movements.
The patient was diagnosed with secondary open angle glaucoma secondary
to pseudoexfoliation syndrome and left visually significant cataract.
The symptoms of substantial IOP elevations were explained and the patient
was instructed to contact their clinician immediately should they experience
these. This patient was commenced on topical treatment with travoprost
once daily OU and left cataract extraction was arranged. After 2 months,
IOP fell to 20 and 22 mmHg. In view of the low central corneal thickness,
target IOPs for this patient should be in the low or mid teens. IOPs
were therefore rechecked and found to be OD 18 and OS 17mmHg. An arrangement
was made to closely monitor this patient to ensure IOPs remain at, or
preferably below this level. Subsequent uncomplicated cataract extraction
improved left visual acuity to 20/30.
1. Signs of pseudoexfoliation can be subtle. Although some patients
have iris atrophy, often most obvious at the pupil margin, many individuals,
like this patient do not exhibit this. Pupil dilation therefore greatly
aids diagnosis. Although variable degrees of angle pigmentation are
common in this condition, pseudoexfoliative material is less easy to
2. Although PXF material may be visible unilaterally, it should be regarded
as a bilateral but asymmetric condition.
3. Irregular angle pigmentation should alert the examiner to the possibility
of pseudoexfoliation syndrome. Differential diagnoses include uveitis,
Fuchs heterochromic iridocyclitis, previous trauma, and pigment
4. IOP level in pseudoexfoliative glaucoma can be exceptionally high
for an open-angle state, and can be sufficient to cause corneal oedema
with symptoms usually associated with sub-acute angle closure episodes.
These variations are usually cyclic and so diurnal IOP measurement may
be beneficial. These IOP spikes, or otherwise poor intraocular pressure
control, can lead to progression at a rate much greater than that found
in primary open angle glaucoma.
5. Pseudoexfoliation is associated with zonular weakening that can increase
the chance of peroperative complications in cataract extraction. Care
should be taken to ensure surgeons are fully aware of the diagnosis.
6. Pseudoexfoliation syndrome is likely to be a systemic condition,
with involvement of other organs. Some reports describe associations
with cerebrovascular and cardiovascular disease, although no evidence
supports greater mortality rates amongst patients with pseudoexfoliative
Paul GD Spry, PhD, BSc, MCOptom, DipGlauc
FROM THE EXPERTS
avoid the need to leaf through a large record of a patient with chronic
glaucoma, it helps to have on the face sheet or problem list of the
patient's chart a statement like: "Discovered in 1998 to have moderate
cupping and field loss with IOP 25/22, confirmed 24/22 a week later
before treatment". One may also then record a target pressure,
remembering that it is tentative, or simply leave it implied by the
statement of the pre-treatment pressure. As time goes on, the highest
pressure ever recorded on or off treatment might also be recorded on
the face sheet of the chart. Of course, the initially stated target
is tentative, and after a few years, the course of events is a better
guide to whether the IOP control is adequate or needs to be more aggressive.
Remember that one doesn't always reach goals in life, and if something
close to the initially stated target is achieved, and if to get more
IOP lowering involves risk and side effects, one might accept a less
ambitious goal, depending on the severity of the disc and field damage.
Also, if progression occurs despite having reached the initial goal,
one is permitted to change the target to a lower IOP.
So while I like the idea that the chart has recorded on its front page
the pre-treatment pressure and the maximum pressure ever observed, it
also seems a good idea to record as a reminder about what you may have
expressed to the patient, that you are going to aim for a certain target
pressure if you can get it easily enough, and if it proves difficult
you will re-evaluate (and you can even write a range for target, "will
try for 15 but accept 17". But putting the number down reminds
you of what you told the patient, so you can say, "We have been
aiming for 16 mm Hg, but with topical PG, beta-blocker, and CAI we have
only achieved 17, and we have even tried laser. Before we contemplate
filtration surgery, let's see what happens over the next 12 months,
and if everything is stable we may put off being more aggressive".
We can't fool ourselves into thinking that when we set an initial target
pressure it is anything more than an educated guess, which for some
people may be more IOP-lowering than needed and for others an insufficient
I do not like the idea of NOT placing in the record something that helps
me take care of the patient. Some people advocate not placing a target
pressure in the record for the reason that there is risk of legal proceedings
if the target is not met and there is visual loss. In fact, if it helps
me care for my patients to have some number in mind and to write it
down (I'm certainly not going to remember the target for every patient),
then I take the stand that it compromises my first duty to my patients
if I fail to write it down. I think it is a defensible position to say
that the degree of IOP-lowering required is different for each individual,
that you set an initial goal, but continually evaluate whether that
goal is adequate and how necessary it is to reach that goal as you contemplate
using more aggressive therapy when initial therapy failed to reach the
Douglas R. Anderson, MD
Diurnal IOP Fluctuation Associated with Glaucoma?
The major randomised clinical trials (RCTs) published on glaucoma over
the past few years have provided strong and irrefutable evidence for
treatment by reduction of IOP. These trials were reviewed in the OGS
EJ volume 1 issue 2. Although each of these addresses a
specific question, there is little doubt that their consensus indicates
IOP lowering improves the glaucoma prognosis, in terms of both reducing
the risk of initial development in ocular hypertension, (1) and of progression
in those with an existing glaucoma diagnosis (2, 3, 4).
RCTs provide highest quality methodology for investigating the effects
of an exposure, such as IOP lowering, on an outcome, such as glaucoma
progression. The reasons for this are (a) they estimate the group effect
of the exposure on the outcome and (b) they minimize the potentially
devastating effects of bias and confounding effects that may inadvertently
produce spurious results in other study designs. However, interpretation
and generalisation of RCT results still requires caution. For example;
standard operating procedures necessary in multicentre RCTs are unlikely
to be representative of routine clinical practice; group effects may
not apply to all individuals; and the way in which data were collected
may not enable all aspects of a variable to be completely explored.
In the context of IOP, the well-known RCTs have not explored the impact
of diurnal IOP variations on glaucoma. It is reasonable to hypothesise,
given two individuals with the same mean IOP over a 24hour period, that
the individual with greater diurnal IOP variation may be at greater
risk of progressive glaucoma. Versions of this hypothesis have been
explored by a number of investigators. One prospective cohort study
recruited 64 glaucoma patients to perform baseline home-tonometry using
self-administered applanation tonometry five times per day (waking,
noon, mid-afternoon, evening and before bed) for 1 week. They then followed
this group over a 5 year period. This study found that individuals with
both greater diurnal IOP and larger IOP range over multiple days were
at higher risk of progressive visual field loss (5). Conversely, a prospective
study measuring IOP throughout office-hours amongst ocular hypertensive
patients found no independent association between diurnal IOP variation
and conversion to glaucoma (6). A recently published abstract of an
observational study measuring IOP 5 times over 24hrs concluded that
the apparent positive association between greater diurnal IOP amplitude
and progressive glaucoma may be the result of the close relationship
between diurnal range and mean IOP (7).
So, what is the true relationship between diurnal IOP variation and
glaucoma? Can it be teased out from these conflicting pieces of evidence?
Regrettably, at the present time, there appears to be no consensus.
In the meantime, the pragmatic approach to understanding these data
and assimilating them into clinical practice may be to remember that
office IOP measurements do not provide a complete picture of IOP control,
each measurement being a single sample, and to challenge the concept
of good IOP control when the degree of glaucoma or progression seem
disproportionate to the apparent IOP (8, 9).
It seems as if the ideal way to determine the relationship between diurnal
IOP variation and glaucoma requires a RCT using diurnal IOP variation
as an exposure variable.
Paul GD Spry, PhD, BSc, MCOptom, DipGlauc
1. Kass MA, Heuer DK, Higginbotham EJ, Johnson CA, Keltner JL, Miller
JP, Parrish RK 2nd, Wilson MR, Gordon MO (2002). The Ocular Hypertension
Treatment Study: a randomized trial determines that topical ocular hypotensive
medication delays or prevents the onset of primary open-angle glaucoma.
Arch Ophthalmol; 120(6):701-13.
2. Leske MC, Heijl A, Hussein M, Bengtsson B, Hyman L, Komaroff E (2003).
Early Manifest Glaucoma Trial Group. Factors for glaucoma progression
and the effect of treatment: the early manifest glaucoma trial. Arch
3, Lichter PR, Musch DC, Gillespie BW, Guire KE, Janz NK, Wren PA, Mills
RP (2001). CIGTS Study Group. Interim clinical outcomes in the Collaborative
Initial Glaucoma Treatment Study comparing initial treatment randomized
to medications or surgery. Ophthalmology; 108(11):1943-53
4. The AGIS Investigators (2000).The Advanced Glaucoma Intervention
Study (AGIS): 7. The relationship between control of intraocular pressure
and visual field deterioration. Am J Ophthalmol; 130(4):429-40.
5. Asrani S, Zeimer R, Wilensky J, Gieser D, Vitale S, Lindenmuth K
(2000). Large diurnal fluctuations in intraocular pressure are an independent
risk factor in patients with glaucoma. J Glaucoma; 9(2):134-42.
6. Bengtsson B, Heijl A (2005). Diurnal IOP fluctuation: not an independent
risk factor for glaucomatous visual field loss in high-risk ocular hypertension.
Graefes Arch Clin Exp Ophthalmol; 243(6):513-8.
7. Jonas JB, Budde WM, Stroux A, Oberacher-Velten IM, Junemann A (2006).
Diurnal intraocular pressure profiles and progression of chronic open-angle
glaucoma. Eye. Apr 7; [Epub ahead of print]
8. Hughes EH, Spry PGD, Diamond JP (2003). Phasing of intra-ocular pressure
in glaucoma management: three case reports and a retrospective review.
J Glaucoma; 12(3): 232-236.
9. Barkana Y, Anis S, Liebmann J, Tello C, Ritch R (2006). Clinical
utility of intraocular pressure monitoring outside of normal office
hours in patients with glaucoma. Arch Ophthalmol; 124(6):793-7.
QUESTIONS AND ANSWERS
What are the emerging protocols for integration of SLT into the treatment
Steven J. Gedde, MD answers:
Since its introduction by Wise and Witter in 1979 (1), laser trabeculoplasty
has been a valuable treatment for patients with open-angle glaucoma.
There has been considerable debate regarding the position of this procedure
in the treatment algorithm for glaucoma. Traditionally, laser trabeculoplasty
has been used as a supplement to maximum tolerated medical therapy or
in patients who are poorly compliant with medical therapy. However,
many clinicians have advocated use of laser trabeculoplasty as an initial
therapy for glaucoma because of its safety and efficacy. The Glaucoma
Laser Trial (GLT) enrolled 271 patients with newly diagnosed open-angle
glaucoma and randomized them to initial treatment with argon laser trabeculoplasty
(ALT) in one eye and a stepped medical regimen beginning with timolol
0.5% in the other eye. After two years of follow-up, significantly
more patients had controlled intraocular pressure (IOP) with ALT alone
(44%) than timolol alone (30%)(2) Despite the results of the
GLT, a survey of members of the American Glaucoma Society showed that
92.9% of responders never or rarely used ALT as initial therapy
The introduction of selective laser trabeculoplasty (SLT) has prompted
a reassessment of the role of laser trabeculoplasty in the treatment
of glaucoma patients. SLT uses a frequency-doubled Nd:YAG laser that
selectively targets pigmented trabecular meshwork cells without damaging
nonpigmented cells (4,5). Unlike ALT, SLT does not cause thermal damage
to the adjacent trabecular meshwork and may be a procedure that can
be performed multiple times. Although there is a strong theoretical
basis for the repeatability of SLT, supporting data is not yet available.
Randomized prospective studies comparing ALT and SLT have reported similar
IOP reduction with both procedures (6-8). A recent prospective, nonrandomized
study found SLT was equally efficacious as latanoprost in lowering IOP
in newly diagnosed open-angle glaucoma and ocular hypertension after
one year (9). An ongoing multicenter randomized clinical trial (SLT/MED
study) is comparing SLT with medical therapy as an initial treatment
for open-angle glaucoma. A patient group in which SLT may have an advantage
over ALT includes those who have had prior ALT. SLT was found to be
more effective than ALT in patients who received prior ALT in one study
(6), and another study reported that the pressure-lowering effect of
SLT was independent of previous ALT (10). Practice patterns appear to
be changing with respect to use of laser trabeculoplasty. An examination
of trends in Ontario, Canada showed there was a substantial reduction
in the number of laser trabeculoplasties performed between 1997 and
2001 coinciding with the introduction of new glaucoma medications, and
the number of laser trabeculoplasties significantly increased between
2002 and 2004 coinciding with the introduction of SLT (11).
Steven J. Gedde, MD, is Associate Professor of Ophthalmology and
Residency Program, Director at Bascom Palmer Eye Institute
1. Wise JB, Witter SL (1979). Argon laser trabeculoplasty for open-angle
glaucoma: A pilot study. Arch Ophthalmol; 97:319-322.
2. Glaucoma Laser Trial Research Group (1990). The Glaucoma Laser Trial
(GLT) 2. Results of argon laser trabeculoplasty versus topical medicines.
3. Schwartz A (1993). Argon laser trabeculoplasty in glaucoma: Whats
happening (survey results of American Glaucoma Society members). J Glaucoma;
4. Latina MA, Park C (1995). Selective targeting of trabecular meshwork
cells: In vitro studies of pulsed and CW laser interactions. Exp Eye
5. Kramer TR, Noecker RJ (2001). Comparison of the morphologic changes
after selective laser trabeculoplasty and argon laser trabeculoplasty
in human eye bank eyes. Ophthalmology; 108:773-779.
6. Damji KF, Shah KC, Rock WJ, et al (1999). Selective laser trabeculoplasty
vs argon laser trabeculoplasty: A prospective randomised clinical trial.
Br J Ophthalmol; 83:718-722.
7. Popiela G, Muzyka M, Szelepin L, et al (2000). Use of YAG-Selecta
laser and argon laser in the treatment of open angle glaucoma. Lin Oczna;
8. Martinez-de la Casa JM, Garcia-Feijoo J, Castillo A, et al (2004).
Selective vs argon laser trabeculoplasty: Hypotensive efficacy, anterior
chamber inflammation, and postoperative pain. Eye; 18:598-502.
9. McIlraith I, Strasfeld M, Colev G, Hutnik CML (2006). Selective laser
trabeculoplasty as initial and adjunctive treatment for open-angle glaucoma.
J Glaucoma; 15:124-130.
10. Chen E, Golchin S, Blomdahl S (2004). A comparison between 90 degrees
and 180 degrees selective laser trabeculoplasty. J Glaucoma; 13:62-65.
11. Rachmiel R, Trope GE, Chipman ML, et al (2006). Laser trabeculoplasty
trends with the introduction of new medical treatments and selective
laser trabeculoplasty. J Glaucoma;15:306-309.
There is a new tonometer available, Diaton, that takes intraocular pressure
through the eyelids. Are there any available studies to compare this
instrument with accepted tonometers on the market today? How accurate
are they with inexperienced versus experienced users (in other words,
is there a steep learning curve to adapt to the device)? I do a lot
of nursing home work and would appreciate a tonometer that doesn't need
a contortionist to use it with some of the residents that I see.
Algis J Vingrys, BScOptom PhD answers:
There are three methods for non-eye contact but through the eyelid tonometry
that I have uncovered: 1. digital palpation, 2. pressure phosphene tonometry
and 3. transcleral tonometry. The device that you refer to is in the
latest of these groups and is marketed in the USA as the Diaton tonometer.
Of the manufacturers claims, I found that measuring IOP in the
presence of: chronic conjunctivitis, corneal erosion, post corneal-surgery,
corneal edema or haze, perhaps the most compelling for its adoption.
As the IOP is measured through the lid it has also been shown to be
unaffected by corneal thickness. It can be used with uncooperative patients
or children and the maker claims that reliable IOP readings can be achieved
after practice on some 50 people.
How do these methods compare to Goldmann applanation tonometry? Herse
et al (1) compared the phosphene method in 107 people and found
poor reliability (+/-8 mmHg 95% limit of agreement). Poor reliability
has also been consistently reported by the many trials listed below
(1-6) for the transcleral method. Perhaps the most interesting trial
was that of Troost et al (2) where they compared both the transcleral
method and digital palpation with Goldmann applanation tonometry (GAT).
Transcleral methods gave readings within 3 mmHg of GAT IOP in 62%
of cases and palpation did likewise in 57%. My enquiry with a glaucoma
specialist familiar with pediatric exams, turned out that this clinician
uses digital palpation as a screening method in neonatal wards, most
of the time. For elderly patients who are unable to be examined using
a slit-lamp or other device that uses a fixed chin-rest, a portable
contact device, such as either the Tonopen, has been shown to exhibit
high measurement accuracy (7,8) and this instrument, or the Perkins
tonometer may remain preferable options.
Algis J Vingrys, BScOptom, PhD
1. Herse P, et al. (2005) The Proview Eye Pressure Monitor: influence
of clinical factors on accuracy and agreement with the Goldmann tonometer.
Ophthalmic Physiol Opt.; 25(5):416-20.
2. Troost A, et al (2005). Transpalpebral tonometry: reliability and
comparison with Goldmann applanation tonometry and palpation in healthy
volunteers. Brit J Ophthalmol ; 89: 280-283.
3. Lam et al. The validity of a digital eyelid tonometer (TGDc-01) and
its comparison with Goldmann applanation tonometry - a pilot study.
Ophthalmic Physiol Opt. 2005; 25(5):205-210.
4. Losch A, et al (2005). Transpalpebral measurement of intraocular
pressure using the TGDc-01 tonometer versus standard Goldmann applanation
tonometry. Graefes Arch Clin Exp Ophthalmol.; 243(4):313-6.
5. Sandner D, et al (2005) Measurement of the intraocular pressure with
the "transpalpebral tonometer" TGDc-01 in comparison with
applanation tonometry. Graefes Arch Clin Exp Ophthalmol; 243(6):563-9.
6. Troost A, et al (2005). Deviations between transpalpebral tonometry
using TGDc-01 and Goldmann applanation tonometry depending on the IOP
level. Graefes Arch Clin Exp Ophthalmol ;243(9):853-8.
7. van der Jagt LH, Jansonius NM (2005) Three portable tonometers, the
TGDc-01, the ICARE and the Tonopen XL, compared with each other and
with Goldmann applanation tonometry. Ophthalmic Physiol Opt; 25(5):429-35
8. Nakamura M, Darhad U, Tatsumi Y, Fujioka M, Kusuhara A, Maeda H,
Negi A (2006). Agreement of rebound tonometer in measuring intraocular
pressure with three types of applanation tonometers.Am J Ophthalmol;
OGS member presentations at the forthcoming
American Academy of Optometry Meeting in Denver.
Joseph Sowka, OD. Topographical analysis of the optic nerve in migraine
sufferers. Program no. 065065.
Elliot M. Kirstein, OD. Paradoxical IOP in Post RK Patient with Pigmentary
Glaucoma (Glaucoma grand round).
Leo P Semes, OD. Sleep apnea syndrome represents a risk for glaucoma
in a veterans affairs population. Program no. 065217.
Michael Sullivan-Mee, OD. Comparison of diurnal intraocular pressure
profiles between dynamic contour tonometry and Goldmann Applanation
tonometry. Program no. 060052.
David Sendrowski, OD. Acquired toxoplasmosis in an immunocompetent patient
from a petting zoo. Program no. 065324.
RESULTS FROM OGS EJ VOLUME 1, ISSUE 4
Our respondents are divided on the value of monocular
trials to assess effectiveness of initial therapy with anti-glaucoma
medications. Fifty-seven percent incorporated monocular trials into
their clinical practice prior to the debate featured in our last
issue, however 12% indicated they will not continue to do
this. Forty-two percent of respondents did not favor monocular trials
and had not incorporated these into practice.
While many tonometers were represented in our survey, the vast majority
(76%) reported normally using Goldmann-type applanation tonometers.
Non-contact tonometers are used by 15%. Approximately 10% used other
forms of tonometry, including the Tonopen, to assess their patients
The frequency of intraocular pressure measurement in stable glaucoma
patients may be difficult to quantify. It is likely clinicians consider,
among other things, the extent of damage and the amount of time the
patient has been stable. These issues speak to the need to individualize
management of our glaucoma patients. Our responses reflected this complexity
with 49% indicating three times a year; 34% less frequently, 17% more
frequently. Ninety-two percent agreed that checking the intraocular
pressure at least two times a year in stable glaucoma patients was the
practice they followed.
Thanks to all those who responded. We encourage all readers to participate.
Paul Spry PhD MCOptom
Brad Fortune, OD,
Shaban Demirel, BScOptom,
Algis Vingrys BScOptom,
Douglas Anderson MD
Paul Artes PhD MCOptom
Dick Bennett OD
Murray Fingeret, OD
Ron Harwerth, PhD
Chris Johnson, PhD
Tony Litwak, OD
John McSoley, OD
Ron Melton, OD
Bruce Onofrey, OD, RPh
Leo Semes, OD
Randall Thomas, OD
Thom Zimmerman, MD, PhD
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