Diagnosis of POAG
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Transcript of Diagnosis of POAG
Primary Open Angle Glaucoma
The comprehensive initial glaucoma evaluation (history and physical examination) includes all
components of the comprehensive adult eye evaluation (Preferred Practice Patterns Committee, 2005)
in the addition to and with special attention to those factors that specifically bear upon the diagnosis,
course, and treatment of primary open-angle glaucoma (POAG). Completion of the evaluation may
require more than one visit. For instance, an individual might be identified as having glaucoma on one
visit but may return for further evaluation, including additional intraocular pressure (IOP)
measurements, central corneal thickness determination, visual field assessment, and optic nerve head
evaluation and documentation.
History
The comprehensive initial glaucoma evaluation includes a review of ocular, family, and systemic
history. It also includes an assessment of the impact of visual function on daily living and activities;
review of pertinent records with particular reference to the status of the optic nerve, visual field, and
IOP; ocular surgery; the use of ocular and systemic medications; known local or systemic intolerance
to glaucoma medications; adherence to the treatment regimen and time of last use of glaucoma
medications; and severity and outcome of glaucoma in family members, including history of visual
loss from glaucoma.
Physical Examination
Visual acuity testing
Typically involves the Snellen chart; conducted in order to
quantitatively measure the ability of each eye to see standardized
letter or number sizes accurately
Pupil
The pupils are examined for reactivity and an afferent pupillary defect.
Anterior Segment
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A slit-lamp bimicroscopic examination of the anterior segment can provide evidence of physical
findings associated with narrow angles, corneal pathology, or a secondary mechanism for
elevated IOP such as pseudo-exfoliation, pigment dispersion, iris and angle neovascularization, or
inflammation.
o Cornea - Signs of microcystic edema (found only with acute elevation
of IOP); keratic precipitates, pigment on endothelium (Krukenberg
spindle); congenital anomalies
o Anterior chamber - Cell or flare, uveitis, hyphema, angle closure
o Iris - Transillumination defects, iris atrophy, synechiae, rubeosis,
ectropion uveae, iris bombe, difference in iris coloration bilaterally
(eg, Fuchs heterochromic iridocyclitis), (PXF) material
o Lens - Cataract progression (ie, signs of phacomorphic glaucoma,
pseudoexfoliation, phacolytic glaucoma with a Morgagnian cataract)
o Fundus - Other abnormalities that could account for any non-
glaucomatous visual field defects or vision loss present (eg, disc
drusen, optic pits, retinal disease), vitreous hemorrhage, or
proliferative retinopathy.
Intraocular Pressure (Tonometry)
Intraocular pressure is measured in each eye, preferably
using a contact applanation method (typically a Goldmann
tonometer) before gonioscopy or dilation of the pupil.
Time of day should be recorded because of diurnal
variation. The assessment may benefit from determining
diurnal IOP fluctuations, either on the same day or on
different days, which may be indicated when disc damage
exceeds the amount expected based on a single IOP
measurement.
The normal range of IOP is between 10 mm Hg and 21 mm
Hg, and is routinely evaluated by tonometry.
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o IOP varies from hour-to-hour in any individual. The circadian rhythm of IOP usually causes it
to rise most in the early hours of the morning; IOP also rises with a supine posture.
o When checking IOP, measurements for both eyes, the method used (Goldmann applanation
is the criterion standard), and the time of the measurement should all be recorded.
o Previous tonometry readings, if available, should be reviewed (eg, Is the reading
reproducible? What method was used to obtain the reading? What time of the day was it?
Where does it fall on the diurnal pressure curve? Do both eyes have similar
measurements?).
o In obese patients, the possibility of a Valsalva movement causing an
increased IOP should be considered when measured in the slit lamp
by Goldman applanation. Measurement should be tried via Tono-
Pen, Perkins, or pneumotonometer with the patient resting back in
the examination chair.
o A difference between the 2 eyes of 3 mm Hg or more indicates
greater suspicion of glaucoma. An average of 10% difference between individual
measurements should be expected. The measurements should be repeated on at least 2-3
occasions before deciding on a treatment plan. The measurement should be completed in
the morning and at night to check the diurnal variation, if possible. (A diurnal variation of
more than 5-6 mm Hg may be suggestive of increased risk for POAG.) Early POAG is
suspected strongly when a steadily increasing IOP is present.
Pachymetry affects applanation tonometry values and, therefore, should be checked on the initial
examination
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Visual field testing
Perform automated threshold testing to rule out any glaucomatous visual field defects. If the
patient is unable to perform automated testing, Goldmann testing may be substituted.
Caveats about visual field analysis
o New-onset glaucomatous defects are found most commonly as an early nasal step, temporal
wedge, or paracentral scotoma (more frequent superiorly); generalized depression related
to IOP level also can be found.
o Swedish interactive thresholding algorithm (SITA)-based software algorithms may decrease
testing time and boost reliability, especially in older patients.
o SWAP (short wavelength automated perimetry or blue-yellow perimetry) may provide a
more sensitive method of detecting visual field deficits, especially in those previously
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labeled as ocular hypertensive. If the Humphrey visual field testing results are normal, SWAP
should be considered to help detect visual field loss earlier. Recent studies suggest SWAP
may detect visual loss/progression up to 3-5 years earlier than conventional perimetry, as
well as in 12-42% of patients previously diagnosed with only OHT. Because the testing time
may be lengthened, it may be tiring for some patients. However, new SITA-SWAP algorithm
software may speed up the testing time and thus improve reliability.
o Frequency doubling perimetry (also called frequency doubling technology or FDT, which is
enhanced with MATRIX software) is a newer technology that projects an alternating pattern
of gridlines onto a screen and stimulates specific neurons that may be damaged early in OHT
or POAG. As in SWAP, this may also be able to help detect nerve fiber layer loss at an earlier
stage in the glaucomatous disease process, thereby screening out more people who are
currently misdiagnosed as having OHT instead of early POAG. Current sensitivities and
specificities are continually improving, but continued baseline data is needed to determine
in what setting this newer technology will prove to be most useful.
o Examination results must take into account that visual field defects may not be apparent
until over 40% loss of the nerve fiber layer has occurred. Therefore, the therapy should be
based on the overall clinical picture and not on visual field testing alone.
o The pupil size should be documented at each testing session, as constriction can reduce
retinal sensitivity and mimic progressive field loss.
o Risk factors, specifically for the development of glaucomatous field loss in OHT, have
recently been studied, and it was found that several presumed risk factors (ie, presence of
hypertension, diabetes, refractive error, race, family history of glaucoma, gender, smoking
or ethanol use, disc area) were not significant for prediction of eventual field loss.
o Significant positive predictive factors of field loss included higher IOP, older age, and
presence of a disc crescent, larger cup-to-disc ratio, smaller rim-disc area ratio, and cup
asymmetry. Consequently, the relationship of risk factors for OHT and POAG compared with
that of actual field loss development is much more complex than has been previously
presumed.
o The initial visual field baseline may need to be repeated at least twice on successive visits,
especially if initial testing shows low reliability indices. Newer glaucoma progression analysis
(GPA) software can help identify reliable perimetric baselines, and probability-based
analyses of subsequent fields can assist in determining if there is true progression over time
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versus artifact. In follow-up, if a low risk of onset of glaucomatous damage is present, then
repeat testing may be performed once a year. If a high risk of impending glaucomatous
damage is present, then testing may be adjusted (as frequent as every 2 mo).
Central Corneal Thickness (CCT)
Measurement of central corneal thickness (CCT) aids the
interpretation of IOP measurement results and
stratification of patient risk. Measurement methods include
ultrasonic and optical pachymetry.
Owing to the sensitivity of all methods of tonometry to
corneal thickness, methods such as Goldmann tonometry
should be augmented with pachymetry to measure central
corneal thickness (CCT).
A thicker-than-average cornea can result in a pressure
reading higher than the 'true' pressure, whereas a thinner-than-average cornea can produce a
pressure reading lower than the 'true' pressure.
Because pressure measurement error can be caused by more than just CCT (i.e, corneal
hydration, elastic properties, etc.), it is impossible to 'adjust' pressure measurements based only
on CCT measurements. The Frequency Doubling Illusion can also be used to detect glaucoma with
the use of a Frequency Doubling Technology (FDT) perimeter. Examination for glaucoma also
could be assessed with more attention given to sex, race, history of drugs use, refraction,
inheritance and family history.
Gonioscopy
Measurement of the angle between the cornea and the iris to assess whether the glaucoma is
open or closed angle. Initial assessment only (unless there is a change such as trauma).
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The diagnosis of POAG requires careful evaluation of the anterior-chamber angle to exclude angle
closure or secondary causes of IOP elevation, such as angle recession, pigment dispersion,
peripheral anterior synechiae, angle neovascularization, and trabecular precipitates.
Check the peripheral contour of the iris for plateau iris, and examine the trabecular meshwork for
peripheral anterior synechiae, as well as neovascular or inflammatory membranes.
The Schlemm canal may be seen with blood refluxing through the canal into the posterior
trabecular meshwork. This possibly could indicate elevated episcleral venous pressure, with such
conditions as carotid-cavernous fistula, Graves orbitopathy, or Sturge-Weber syndrome needing
to be ruled out.
Optic Nerve Head and Retinal Nerve Fiber Layer
There is evidence that glaucomatous changes detected with optic
disc and retinal nerve fiber layer analysis may precede changes
detected by standard automated perimetry.
examination of the optic nerve to look for any visible damage to
it, The extent of optic nerve involvement can be accurately assessed
via direct (with) or indirect (using specialized lenses) , which allows
the ophthalmologist to view glaucomatous changes such as cupping
or other signs of damage on the optic nerve such as optic nerve
hemorrhage or focal loss of nerve fiber layer.
Retinal nerve fiber analysis may aid in monitoring the progression of
glaucomatous optic neuropathy in at-risk individuals.
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The retinal nerve fiber layer can be assessed with imaging techniques such as optical coherence
tomography (OCT), scanning laser polarimetry (GDx), and/or scanning laser ophthalmoscopy also
known as Heidelberg Retina Tomography (HRT3).
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References
© http://www.sbu.se/en/Published/Yellow/Open-Angle-Glaucoma-Diagnosis-Follow-up-
and-Treatment/
© http://www.guideline.gov/summary/summary.aspx?ss=15&doc_id=8203
© https://www.merck.com/mmpe/sec09/ch103/ch103b.html
© http://www.patient.co.uk/doctor/Primary-Open-Angle-Glaucoma.htm
© http://www.sbu.se/en/Published/Yellow/Open-Angle-Glaucoma-Diagnosis-Follow-up-
and-Treatment/
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