Module 12 Section 2
 

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Module 12:

 Visual Field Testing
 

Section 2:

 The Outer Limits
     
     
 

The Limits of the Visual Field

 

The Confrontation Visual Field Test
     
   
 

 

The Limits of the Visual Field

 

When a patient comes into the office with that too familiar driver’s license vision form, what do you put down for the normal limits of the patient’s visual field? I suspect that the vast majority of us check the limits by the confrontation method. So what is the width in degrees of a normal monocular visual field: 90?, 100?, 120?, 140? How about the degree width of a normal binocular field: 140?, 160?, 180?!

 

Of course, by their very nature, confrontation fields lack precision. How could we more precisely measure the outer limits of a visual field? The tangent screen only measures the central 30 degrees. Automated machines like the Humphrey usually are not set up to measure the limits (see Module 15 for more information on using the HVA to test peripheral vision). The Goldmann field machine does do a good job at measure field limits. Of course the limits measured will depend upon the target size used, but I think that an automobile approaching from the periphery represents a fairly large target size.

 

The figure below  is representative of limits of a normal visual field of the right eye as measured with the Goldmann perimeter using a 3mm white target.  Each concentric circle on the graph represents 10 degrees.
   
 
   
  The Ophthalmic Assistant describes the limits as being 60 degrees upward, 75 degrees downward, 60 degrees inward (nasally), and 95 degrees outward (temporally). It goes on to say that if a larger target is used (perhaps such as a finger, or an automobile), then the temporal limit is pushed to 110 degrees. Other books also describe the temporal limit as being 90 degrees plus. The limits of the normal field are often depicted as shown in the diagram below of the left eye Goldmann visual field, illustrating how the nose limits the "nasal" field to about 60 degrees.
   
 
   
  Look what happens when we overlap the fields of the left eye and the right eye (pictured below).  The circle in the middle, the visual field common to both eyes, represents the area of binocular vision.  It is roughly 120 degrees wide.
   
 
   
 

Consider the temporal field limits.

   
 
 

It the temporal field does indeed extend to 90 degrees or beyond, doesn't that mean that light would have to be "going around a corner"?

 

Some argue that it is impossible for the temporal limit to be 90 degrees or greater. When performing Goldmann perimetry some people do respond to a stimulus presentation at the 90 degree angle and beyond.  Apparently the cornea does bend the light around the corner.

 
  In practical terms I would argue that it is safe to assume that the "normal" width for monocular visual field is 150 degrees (90 plus 60).
 
  The normal width for a binocular visual field is 180 degrees (90 plus 90).
 
 

The way the question about the visual field is worded tends to vary from state to state. Here in the Kansas City metro area we get driver's license forms from both Kansas and Missouri.

 

The Kansas form asks what the field width is to the right of fixation (90 degrees normally), to the left of fixation (90 degrees normally), and what the total field width is (180 degrees normally).
 
 

The Missouri form asks what the field width for each individual eye is (150 degrees normally), and what the total field width is (180 degrees normally).
 
 

If the patient is monocular, the normal field to the right of fixation, for the right eye for example, would be 90 degrees. The normal field to the left of fixation would be 60 degrees, for a total field width of 150 degrees.

 

 

The Confrontation VF Test

 

The confrontation visual field test is a fast screening field test that will give you fairly accurate limits of the visual field and will detect large field defects.  It should be part of every routine eye exam.

 

The conventional method

 

Most manuals teach that the confrontation field test should be a comparison of the patient's visual field to your own visual field.  Instructions are as follows:

  • The patient sits facing you, about one meter away, without glasses.

  • The patient is instructed to look at your nose and to cover her left eye (the field of the right eye is being tested).

  • You cover your right eye so that your visual fields will correspond.

  • You hold up fingers in each of the visual field quadrants for the patient to count.
 
 
  • If the patient cannot see one or more fingers in any quadrant, then the defect can be explored by placing a small object, such as a cotton tipped applicator, in the non-seeing area and moving it until the object can be seen by the patient.
  • The same procedure is repeated for the left eye.

A problem with the procedure as described above is that the limits of the visual field are not tested.  The normal horizontal limits of our patient's visual field are depicted by the green line.
 
  If we are able to stretch to test the limits of the patient's field, then we are no longer comparing the patient's visual field to our visual field.
 
 

 

A better method for confrontation field testing

 

Why not use our knowledge of the extent of the normal visual field to more efficiently perform the confrontation field test.  When testing the right eye:

  • Have the patient occlude the left eye and look at a fixation target straight ahead with the right eye.  Instruct the patient to maintain fixation and to let you know when your target is first seen.

  • Sit to the patient's right.  You will need to watch the patient's eye to make sure that fixation is being maintained. Using your knowledge of where the limits of the field should be,  move a target from behind the patient (non-seeing) toward the horizontal limit of the field.  The patient tells you when it comes into view and you make a mental note of where it was seen within the context of where the boundaries of a normal field should be.
 

 

  • Do the same for the superior, superior/temporal, inferior, and inferior/temporal limits of the field.  Remember that the the superior field will be about 60 degrees, limited by the eyebrow.  The inferior field will be about 75 degrees down, limited by the cheek.

  • The space within the normal field boundaries can be explored with a small test object.  The patient simply tells you when it is visible and when it is not.  The finger counting technique can also be used.
 

 

  • The limit of the nasal side of the visual field is tested by moving to the other side of the patient, and again moving from non-seeing to seeing, until the patients indicates that the target is seen.  The limits of the superior/nasal and inferior/nasal fields are also tested from this side.
 

 

  • The visual field of the left eye is tested in a similar fashion, beginning with you on the patient's left, which is where you ended up when testing the right eye.
 

A defect found using the confrontation method can be easily and effectively drawn by use of a simple diagram. 
 

 

Remember that the fields should be drawn as the patient sees, so the diagram of the right visual field is on the right.  The confrontation field of a bitemporal hemianopsia would look like this:
 

 

Simply scribble in the area that cannot be seen by the patient.  (And you thought kindergarten was a waste of time.)

 

When performing the confrontation field test on a patient with a bitemporal hemianopsia, the patient would only see in the area shaded by green, as pictured below.  The top picture shows the right eye being tested, and the bottom pictures shows the left eye being tested.
 

 

 
 

 

 
 

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