We have concerns about the report by Cavanaugh et al. [1]: Our major concern is that they
may not have separated the potential effects of training on improving attention along the
vertical meridian. [1] By learning to focus attention along the vertical meridian,
improvements could be explained at least in part.
In addition, the Humphrey device does not adequately capture small eye movements
(fixation shifts). How did the authors establish that they had one degree of precision
with this relatively low resolution eye tracker. Fixation shifts of up to 3-5 degrees are
common in perimetry. [2]
Too much is made of differences in dB values below about 15 dB. We have shown the
variability is so high below 15 dB that the most frequent value on retest is 0 dB. [2]
There is broad agreement that the retest variability below 15 dB has little predictive
value. [3]
The Idiopathic Intracranial Hypertension Treatment Trial did not conclude a change
of 0.7 dB mean deviation as clinically significant, only that the change was statistically
significant nor did the Tattersall et al. article cited by the authors. The mean deviation
change that is clinically significant has not been determined.
It does not appear that the authors accounted for the perimetric learning effect
that is greatest from session one to session two, but may persist for additional tests.
[4,5]
The spatial resolution of the HFA test used is six degrees. Therefore, a gain of
sensitivity in one test location (which may well result from a small spontaneous fixation
shift or one related to extra attention along the vertical) would result in a gain in area
by 36 degrees. [2] The reported effects in this study appear to be at least partially
explained by attention related fixation shifts resulting in responding to more test
locations. The inability to partition improvements due to a better ability to focus
attention along the vertical meridian and the other issues discussed confound
interpretation of the results in this study.
1. Cavanaugh MR, Huxlin KR. Visual discrimination training improves Humphrey
perimetry in chronic cortically induced blindness. Neurology 2017;88:1856-1864.
2. Demirel S, Vingrys AJ. Eye Movements During Perimetry and the Effect that
Fixational Instability Has on Perimetric Outcomes. J Glaucoma 1994;3:28-35.
3. Wall M, Woodward KR, Doyle CK, Zamba G. The effective dynamic ranges of
standard automated perimetry sizes III and V and motion and matrix perimetry. Arch
Ophthalmol 2010;128:570-576.
4. Gardiner SK, Swanson WH, Demirel S. The Effect of Limiting the Range of
Perimetric Sensitivities on Pointwise Assessment of Visual Field Progression in Glaucoma.
Invest Ophthalmol Vis Sci 2016;57:288-294.
5. Heijl A and Bengtsson B. The effect of perimetric experience in patients with
glaucoma. Arch Ophthalmol 1996;114:19-22.
For disclosures, please contact the editorial office at [email protected].
We have concerns about the report by Cavanaugh et al. [1]: Our major concern is that they may not have separated the potential effects of training on improving attention along the vertical meridian. [1] By learning to focus attention along the vertical meridian, improvements could be explained at least in part.
In addition, the Humphrey device does not adequately capture small eye movements (fixation shifts). How did the authors establish that they had one degree of precision with this relatively low resolution eye tracker. Fixation shifts of up to 3-5 degrees are common in perimetry. [2]
Too much is made of differences in dB values below about 15 dB. We have shown the variability is so high below 15 dB that the most frequent value on retest is 0 dB. [2] There is broad agreement that the retest variability below 15 dB has little predictive value. [3]
The Idiopathic Intracranial Hypertension Treatment Trial did not conclude a change of 0.7 dB mean deviation as clinically significant, only that the change was statistically significant nor did the Tattersall et al. article cited by the authors. The mean deviation change that is clinically significant has not been determined.
It does not appear that the authors accounted for the perimetric learning effect that is greatest from session one to session two, but may persist for additional tests. [4,5]
The spatial resolution of the HFA test used is six degrees. Therefore, a gain of sensitivity in one test location (which may well result from a small spontaneous fixation shift or one related to extra attention along the vertical) would result in a gain in area by 36 degrees. [2] The reported effects in this study appear to be at least partially explained by attention related fixation shifts resulting in responding to more test locations. The inability to partition improvements due to a better ability to focus attention along the vertical meridian and the other issues discussed confound interpretation of the results in this study.
1. Cavanaugh MR, Huxlin KR. Visual discrimination training improves Humphrey perimetry in chronic cortically induced blindness. Neurology 2017;88:1856-1864.
2. Demirel S, Vingrys AJ. Eye Movements During Perimetry and the Effect that Fixational Instability Has on Perimetric Outcomes. J Glaucoma 1994;3:28-35.
3. Wall M, Woodward KR, Doyle CK, Zamba G. The effective dynamic ranges of standard automated perimetry sizes III and V and motion and matrix perimetry. Arch Ophthalmol 2010;128:570-576.
4. Gardiner SK, Swanson WH, Demirel S. The Effect of Limiting the Range of Perimetric Sensitivities on Pointwise Assessment of Visual Field Progression in Glaucoma. Invest Ophthalmol Vis Sci 2016;57:288-294.
5. Heijl A and Bengtsson B. The effect of perimetric experience in patients with glaucoma. Arch Ophthalmol 1996;114:19-22.
For disclosures, please contact the editorial office at [email protected].