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Threshold Visual Field Testing

Help diagnose advanced vision problems early with a threshold Visual Field at Artisan Optics Boise Idaho

 

Threshold visual fields are a unique test that gives insight to the neurologic function of the eye and brain . A visual field can help detect abnormalities within the eye, within the optic nerve, at the optic chiasm (where the optic nerves cross), and lesions after the chiasm. Threshold visual fields can also help narrow down the location of a brain lesion.  

Test for visual defects with a threshold visual field at Artisan Optics Boise Idaho

 

During optometry school the neuro-optometry professors used to fondly refer to a threshold visual field as “a poor man's brain MRI” because of the precious information provided by this testing. Visual field testing may sometimes be the indicator to help direct further testing to find an ailment. In some cases, threshold visual fields can pick up pathology earlier than an MRI.

 

What is a threshold visual field? A threshold visual field is a measurement of threshold (lowest limit one can see) of the periphery and central vision. The majority of current visual field testing is performed on automated instrumentation that presents stimuli in a stair step fashion starting at non-visible targets and proceeding to visible targets then repeating the same point starting at visible targets and proceeding to non-visible targets. The end point of the threshold measurement is determined when a person is able to see 50% of the presentations at a certain level. While it seems tedious to check these points so many times it is the most accurate method to determine the actual level of cellular response. So each point on a visual field test is actually matched up to a corresponding point on the retina and therefore neurologic pathway.

 

For a quick and dirty explanation of the anatomy of the optic pathway. Obviously the eyes are in the front of the head and the occipital lobe (the visual cortex) is in the back of the head. One would think that the optic nerve runs straight from the eye to the occipital lobe but that is not the case. Once the optic nerve leaves the eye both nerves come together just behind the eyes and cross. The crossing is called the optic chiasm. When the nerves cross a portion of the nerve fibers cross to the opposite side of the brain and a portion of the nerves stay on the same side. These fibers can help correlate to the nasal and temporal portion of the eye's visual field. The nerves then continue through the temporal lobe, parietal lobe, lateral genigulate nucleus and finally to the occipital lobe on both sides of the brain. It has been said that the visual pathway takes up about 40% of the brain. Considering how much real estate the optic pathway travels through it is not a far stretch to imagine it!

 

Now, because the optic pathway splits and traverses the cortical countryside it lays out a map relating to where it has been and is demonstrated on a visual field. So while you may think that we are torturing you during the threshold visual field for minutes on end clicking a button, we are actually taking in information about your brain in a very non-invasive fashion. Remember I mentioned the anatomy explanation was quick and dirty!

 

So what are the types of visual field defects a person can have? Well it varies depending on the condition as well as confounding variables but in general here is a short list of what a visual field can find:

  • Central visual field defects

    • macular degeneration

    • toxic maculopathy (retinal changes associated with certain systemic medications)

    • retinal dystrophies

    • macular damage (macular holes)

    • retinal vascular occlusions

  • Peripheral visual field defects

    • glaucoma

    • retinal detachment

    • peripheral retinal changes

  • Hemianopia visual fields (changes in both visual fields on the same side)

 

Threshold visual fields are a valuable tool to help elicit more information about the integrity of the optic pathway and the health of the eye. It can also help catch pathology before there are symptoms. For some people that annoying “video game” can be a lifesaver.

 

Early detection can be achieved with a threshold visual field at Artisan Optics Boise Idaho

 

Posted by Artisan Optics at 6/28/2016 4:30:00 PM
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