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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