Glaucomas represent a diverse group of diseases that have in common characteristic changes in the optic nerve neuroretinal rim tissue.
An American Academy of Ophthalmology (AAO) ophthalmic technology assessment reported that serial stereophotography of the optic nerve head is considered the reference standard of care for patients with glaucoma.
A more recent assessment of the value of glaucoma tests emphasized that optic nerve examination as performed by a clinical exam or via stereo-disc photographs remains the foundation of glaucoma diagnosis.
Other fundamental factors critical to diagnosis and management include integrating history, examination, as well as other structural and functional assessments.
As the number of patients who have glaucoma grows, having an efficient testing system becomes crucial to appropriately care for them. An efficient testing system is one in which technicians are able to quickly and accurately acquire the data of both functional and structural testing to relate to the doctor.
Here, we review the common glaucoma tests as well as tips for each and links for more resources.
Measuring intraocular pressure (IOP), or tonometry, is essential in assisting in the detection of undiagnosed glaucoma and in identifying disease progression. The Goldmann tonometer is the most commonly used.
Other tonometers include the Icare rebound tonometer, the digital dynamic contour tonometer, and several lightweight handheld tonometers, such as the Tono-Pen (Reichert) and AccuPen (Keeler). A new prism, the CATS Tonometer Reusable Prism, was designed to improve IOP accuracy.
The CATS prism integrates easily with current tonometer equipment.
In terms of functional measurements, visual field testing is the major player. Defects, or blind spots, are the major sign of the disease and a method by which to monitor progression of the disease.
This is done via perimetry, and, most commonly, the Humphrey field analyzer.
OCT aids in diagnosing glaucoma in evaluating both the optic disk and retinal nerve fiber layer (RNFL).
Specifically, images captured can provide an objective evaluation of the optic nerve. Identifying areas of thinning in the RNFL can aid in early detection of the disease as it may be apparent before visual field defects become evident.
Optical pachymeters aid the technician in providing corneal thickness measurement and assessment. Thin corneas, common in those who have undergone laser refractive surgery, can affect tonometry readings. Specifically, it can cause the pressure reading to be lower than the eye’s actual pressure. Correction tables can be helpful to ascertain true IOPs in these patients. A thin cornea itself may also be a risk factor for glaucoma.
Acquired via Ocular Response Analyzer (Reichert), CH measures the cornea’s ability to absorb and dissipate energy. Studies have shown that lower CH values correlate to faster rates of visual field loss.
To obtain optimum visual field test results the technician should remember the following:
When placing multiple lenses in the lens holder, the spherical lens is placed closest to the patient’s eye. Confirm that the axis of the cylinder lens is lined up properly. Also, make sure the lens is close to the eye but not touching. If the lens is too far from the eye, it will induce a rim artifact.
3.The biggest deal breaker in these tests is patient positioning and comfort. For positioning, this requires proper eye alignment with the center and the height of the machine.
Also make sure the chin and forehead stay in contact with the machine. For comfort, if the patient is not comfortable, he will focus on his discomfort instead of the test. As such, once you line up the eye in monitor, ask the patient if he wants the height adjusted for comfort.
Patients must know to fixate at the center target and not move the eye to search for lights, as the test is measuring peripheral vision. Also, patients should be encouraged to blink so the eye does not dry out.
A lot of times there is movement at the beginning of the test, and, if the blind spot measured incorrectly, it will lead to high fixation losses. Finally, encourage the patient throughout the test as positive reinforcement to contribute to good test results.
If this should happen, re-establish understanding and instruct them to only click when lights present and that there are times when no lights are presented. False negatives occur when the patient fails to see a significantly brighter light at a location where the patient was already tested and had responded.
If there are a high number of false negatives, either the patient is not alert/ paying attention or there is pathology in this area.