Reply to: Mallett unit or fully fusionable images for prisms against asthenopia?

Evans, Bruce J. W.; Parmar, Ketan R.; Dickinson, Christine

doi:10.1016/j.optom.2021.09.006

Cited by 2 publications

(3 citation statements)

References 10 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…There is evidence that prescribing prism based on the aligning prism measured with the Mallett unit can improve visual performance and symptoms. [104][105][106] Mallett suggested that the smallest prism needed to neutralize the fixation disparity with the Mallett unit should be prescribed, whereas Sheedy proposed that the prism to be prescribed could be taken as the smallest amount of prism associated with the flat portion of a patient's fixation disparity curve 28,29 To generate the fixation disparity curve necessary to apply this latter criterion, Sheedy originally proposed that the Sheedy disparometer could be used. The fusion lock of the Sheedy disparometer is peripheral to the Nonius lines, and it has been argued that this could lead to results that are less diagnostic than those of a device in which the fusion lock is central.…”

Section: Relationship Of Fixation Disparity To Binocular Symptomsmentioning

confidence: 99%

“…The association between fixation disparity measures and the management of patients with decompensated phoria will only be discussed briefly here (see Evans 27 for a detailed description of decompensated phoria management). There is evidence that prescribing prism based on the aligning prism measured with the Mallett unit can improve visual performance and symptoms 104–106 . Mallett suggested that the smallest prism needed to neutralize the fixation disparity with the Mallett unit should be prescribed, whereas Sheedy proposed that the prism to be prescribed could be taken as the smallest amount of prism associated with the flat portion of a patient's fixation disparity curve 28,29 To generate the fixation disparity curve necessary to apply this latter criterion, Sheedy originally proposed that the Sheedy disparometer could be used.…”

Section: Relationship Of Fixation Disparity To Binocular Symptomsmentioning

confidence: 99%

See 1 more Smart Citation

Topical Review: Methodological Variables in Clinical and Laboratory Measurements of Fixation Disparity

Fogt

2023

Optom Vis Sci

View full text Add to dashboard Cite

Significance Fixation disparity is a small vergence error that does not disrupt fusion. Fixation disparity measures correlate with binocular symptoms. This paper covers methodological differences between clinical fixation disparity measurement devices, findings when objective and subjective fixation disparities are compared, and the potential impact of binocular capture on fixation disparity measurements. Fixation disparity is a small vergence error that occurs in non-strabismic individuals and does not disrupt fusion. This paper reviews clinical fixation disparity variables and their clinical diagnostic value. Clinical devices that are used to measure these variables are described as are studies in which the output from these devices have been compared. Methodological differences between the devices such as the location of the fusional stimulus, the rate at which judgments of dichoptic alignment are made, and the strength of the accommodative stimulus are all considered. In addition, the paper covers theories of the neural origins of fixation disparity and control systems models incorporating fixation disparity. Studies in which objective fixation disparities (oculomotor portion of fixation disparity assessed with an eye tracker) and subjective fixation disparities (sensory portion of fixation disparity assessed psychophysically with dichoptic Nonius lines) have been compared are also examined, and consideration is given to why some investigators find differences in these measures while other investigators do not. The conclusion thus far is that there are likely complex interactions between vergence adaptation, accommodation, and the location of the fusional stimulus that lead to differences in objective and subjective fixation disparity measures. Finally, capture of the visual direction of monocular stimuli by adjacent fusional stimuli and the implications for fixation disparity measures are considered.

show abstract

Section: Relationship Of Fixation Disparity To Binocular Symptomsmentioning

confidence: 99%

Section: Relationship Of Fixation Disparity To Binocular Symptomsmentioning

confidence: 99%

Topical Review: Methodological Variables in Clinical and Laboratory Measurements of Fixation Disparity

Fogt

2023

Optom Vis Sci

View full text Add to dashboard Cite

show abstract

“…For measuring fixation disparity or the aligning prism, clinicians may use the Mallett Unit with stationary presented dichoptic nonius lines. 1 Two recent Letters to the Editor 2 , 3 referred to the practical question whether dichoptic targets may perhaps distort the measurement. 4 In this debate, earlier research on sensory and motor aspects of fixation disparity may be helpful.…”

mentioning

confidence: 99%