Reviewing ocular specialty testing
Familiarize yourself with anterior and posterior testing in your practice
The average adult eye axial length is 24 mm. Variance of that measurement can be seen in myopia, which results in a “longer” eye, and in hyperopia, which results in a “shorter” eye. During pre-operative testing for cataract surgery, an error of 0.33 mm can result in a dramatic post-surgical IOL power deviation of up to 1.00 D.
Posterior segment testing
B scan ultrasonography (brightness scan) is a two-dimensional, cross-sectional view of the eye and orbit. Ultrasound is useful for detecting retinal detachment, tumors, vitreous hemorrhaging, and inflammation and lesions of the eye and orbit.
The eye is anesthetized, and a probe is placed on the eye, and in some cases, the eyelid. The ultrasound echo reveals a black and white picture of the eye and its structures, with the black images being the absence of echo (or structure).
OCT (ocular coherence tomography) use light rays to show a cross-sectional picture of the retina, helping to diagnose a multitude of retinal concerns, such as macular hole, epiretinal membrane, macular edema, and more. Scans of the optic nerve can determine if there is optic nerve thinning, impactful in the diagnosis and treatment of glaucoma.
Visual field or perimetry comes in the form of static or kinetic method.
The static method of visual field testing utilizes lights that change in size and brightness. Most static testing is computerized, yet confrontational field testing is a form of static visual field testing. Computerized static visual field testing is highly patient dependent—proper instructions to patients and monitoring compliance is key for accuracy.
Kinetic testing utilizes moving lights of differing sizes and brightness. While computerized methods of kinetic testing exist, the most commonly used tester is the Goldmann bowl perimetry. Technician training is crucial for accurate and thorough Goldmann field testing.
While it is one of the most complained about types of testing, visual field perimetry can provide valuable information regarding glaucoma damage, stroke damage, or even the presence of a tumor. Understanding the anatomy behind the visual pathway and the visual manifestations of perimetry will give the technician guidance for testing and will also engage the technical staff during the procedure, which can be less than exciting.