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Decreased fixation stability of the preferred retinal location in juvenile macular degeneration.

Bethlehem RA, Dumoulin SO, Dalmaijer ES, Smit M, Berendschot TT, Nijboer TC, Van der Stigchel S - PLoS ONE (2014)

Bottom Line: It is unclear however, whether the preferred retinal locus also develops properties typical for foveal vision.For this purpose, we used the fixation-offset paradigm and tracked eye-position using a high spatial and temporal resolution infrared eye-tracker.In addition, we performed a simulation with the same task in a group of five healthy controls.

View Article: PubMed Central - PubMed

Affiliation: Experimental Psychology, Helmholtz Institute, Utrecht University, Utrecht, The Netherlands; Autism Research Centre, Department of Psychiatry, University of Cambridge, Cambridge, United Kingdom.

ABSTRACT
Macular degeneration is the main cause for diminished visual acuity in the elderly. The juvenile form of macular degeneration has equally detrimental consequences on foveal vision. To compensate for loss of foveal vision most patients with macular degeneration adopt an eccentric preferred retinal location that takes over tasks normally performed by the healthy fovea. It is unclear however, whether the preferred retinal locus also develops properties typical for foveal vision. Here, we investigated whether the fixation characteristics of the preferred retinal locus resemble those of the healthy fovea. For this purpose, we used the fixation-offset paradigm and tracked eye-position using a high spatial and temporal resolution infrared eye-tracker. The fixation-offset paradigm measures release from fixation under different fixation conditions and has been shown useful to distinguish between foveal and non-foveal fixation. We measured eye-movements in nine healthy age-matched controls and five patients with juvenile macular degeneration. In addition, we performed a simulation with the same task in a group of five healthy controls. Our results show that the preferred retinal locus does not adopt a foveal type of fixation but instead drifts further away from its original fixation and has overall increased fixation instability. Furthermore, the fixation instability is most pronounced in low frequency eye-movements representing a slow drift from fixation. We argue that the increased fixation instability cannot be attributed to fixation under an unnatural angle. Instead, diminished visual acuity in the periphery causes reduced oculomotor control and results in increased fixation instability.

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Paradigm overview.Panel A shows a schematic overview of the fixation-offset paradigm as used by Machado & Rafal [32]. After drift correction participants are instructed to keep a steady fixation within the four anchors. As soon as a target appears they are instructed to make an eye-movement to that target as fast as possible. Presently, we focussed on the fixation phase (before target presentation) of this paradigm. Panel B shows the adaptation used in the PRL simulation version of this paradigm. Prior to the normal trial procedure (but after drift correction), participants had to align a gaze-controlled alternate eccentric fixation point over a central fixation cross. This led them to use their peripheral vision to fixate on the central fixation cross before the start of the trial. In panel B the “eyeball” symbol represent the true fixation, the ‘+’ sign represents the central fixation and the circled ‘+’ sign represents the eccentric fixation point that was controlled by the participants eye movement. There was no minimum fixation time during alignment of the eccentric fixation point that participants had to maintain for the trial to start. However, should participants make a saccade directing the eccentric fixation to the central fixation cross and then press the spacebar, the subsequent saccade parser would have detected a saccade at trial start and the trial would have been removed from subsequent analysis.
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pone-0100171-g002: Paradigm overview.Panel A shows a schematic overview of the fixation-offset paradigm as used by Machado & Rafal [32]. After drift correction participants are instructed to keep a steady fixation within the four anchors. As soon as a target appears they are instructed to make an eye-movement to that target as fast as possible. Presently, we focussed on the fixation phase (before target presentation) of this paradigm. Panel B shows the adaptation used in the PRL simulation version of this paradigm. Prior to the normal trial procedure (but after drift correction), participants had to align a gaze-controlled alternate eccentric fixation point over a central fixation cross. This led them to use their peripheral vision to fixate on the central fixation cross before the start of the trial. In panel B the “eyeball” symbol represent the true fixation, the ‘+’ sign represents the central fixation and the circled ‘+’ sign represents the eccentric fixation point that was controlled by the participants eye movement. There was no minimum fixation time during alignment of the eccentric fixation point that participants had to maintain for the trial to start. However, should participants make a saccade directing the eccentric fixation to the central fixation cross and then press the spacebar, the subsequent saccade parser would have detected a saccade at trial start and the trial would have been removed from subsequent analysis.

Mentions: To test fixation characteristics we used a fixation-offset paradigm [32]. All trials started with a drift check to ensure the calibration was still accurate. Participants were instructed to fixate on an unmarked centre containing four eccentric anchors surrounding the unmarked centre (background luminance of 32.07 cd/m2). The unmarked centre served as the fixation point and was located at the centre of the display. The eccentric fixation anchors consisted of four black crosses (0.64°×0.64°) and were presented on the corners of an unmarked square. The distance from the crosses to the centre of the screen was either 3° or 1°. After a pseudo-random interval (between 550 and 950 ms.), a black target circle appeared (diameter of 1.43°). See figure 2A for an overview. In the patient group the location of target dots was dependent of the scotomatous area (either left, right, above or below the eccentric fixation anchor) as target locations that fell within the scotoma, as assessed with a visual field test, were removed from the location possibilities. The eccentric anchors were the same as in the control group to minimize potentially biasing the fixation stability by using different fixation anchors. In the control group targets were presented in all four (left, right, above and below the fixation anchor) possible locations. Participants were instructed to fixate at the unmarked centre until the target dot appeared, and subsequently were to move their eyes as fast as possible to the target circle. The target display was presented for 1500 ms. Afterwards all objects were removed from the display. The experiment consisted of 240 experimental trials and 24 practice trials.


Decreased fixation stability of the preferred retinal location in juvenile macular degeneration.

Bethlehem RA, Dumoulin SO, Dalmaijer ES, Smit M, Berendschot TT, Nijboer TC, Van der Stigchel S - PLoS ONE (2014)

Paradigm overview.Panel A shows a schematic overview of the fixation-offset paradigm as used by Machado & Rafal [32]. After drift correction participants are instructed to keep a steady fixation within the four anchors. As soon as a target appears they are instructed to make an eye-movement to that target as fast as possible. Presently, we focussed on the fixation phase (before target presentation) of this paradigm. Panel B shows the adaptation used in the PRL simulation version of this paradigm. Prior to the normal trial procedure (but after drift correction), participants had to align a gaze-controlled alternate eccentric fixation point over a central fixation cross. This led them to use their peripheral vision to fixate on the central fixation cross before the start of the trial. In panel B the “eyeball” symbol represent the true fixation, the ‘+’ sign represents the central fixation and the circled ‘+’ sign represents the eccentric fixation point that was controlled by the participants eye movement. There was no minimum fixation time during alignment of the eccentric fixation point that participants had to maintain for the trial to start. However, should participants make a saccade directing the eccentric fixation to the central fixation cross and then press the spacebar, the subsequent saccade parser would have detected a saccade at trial start and the trial would have been removed from subsequent analysis.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4061130&req=5

pone-0100171-g002: Paradigm overview.Panel A shows a schematic overview of the fixation-offset paradigm as used by Machado & Rafal [32]. After drift correction participants are instructed to keep a steady fixation within the four anchors. As soon as a target appears they are instructed to make an eye-movement to that target as fast as possible. Presently, we focussed on the fixation phase (before target presentation) of this paradigm. Panel B shows the adaptation used in the PRL simulation version of this paradigm. Prior to the normal trial procedure (but after drift correction), participants had to align a gaze-controlled alternate eccentric fixation point over a central fixation cross. This led them to use their peripheral vision to fixate on the central fixation cross before the start of the trial. In panel B the “eyeball” symbol represent the true fixation, the ‘+’ sign represents the central fixation and the circled ‘+’ sign represents the eccentric fixation point that was controlled by the participants eye movement. There was no minimum fixation time during alignment of the eccentric fixation point that participants had to maintain for the trial to start. However, should participants make a saccade directing the eccentric fixation to the central fixation cross and then press the spacebar, the subsequent saccade parser would have detected a saccade at trial start and the trial would have been removed from subsequent analysis.
Mentions: To test fixation characteristics we used a fixation-offset paradigm [32]. All trials started with a drift check to ensure the calibration was still accurate. Participants were instructed to fixate on an unmarked centre containing four eccentric anchors surrounding the unmarked centre (background luminance of 32.07 cd/m2). The unmarked centre served as the fixation point and was located at the centre of the display. The eccentric fixation anchors consisted of four black crosses (0.64°×0.64°) and were presented on the corners of an unmarked square. The distance from the crosses to the centre of the screen was either 3° or 1°. After a pseudo-random interval (between 550 and 950 ms.), a black target circle appeared (diameter of 1.43°). See figure 2A for an overview. In the patient group the location of target dots was dependent of the scotomatous area (either left, right, above or below the eccentric fixation anchor) as target locations that fell within the scotoma, as assessed with a visual field test, were removed from the location possibilities. The eccentric anchors were the same as in the control group to minimize potentially biasing the fixation stability by using different fixation anchors. In the control group targets were presented in all four (left, right, above and below the fixation anchor) possible locations. Participants were instructed to fixate at the unmarked centre until the target dot appeared, and subsequently were to move their eyes as fast as possible to the target circle. The target display was presented for 1500 ms. Afterwards all objects were removed from the display. The experiment consisted of 240 experimental trials and 24 practice trials.

Bottom Line: It is unclear however, whether the preferred retinal locus also develops properties typical for foveal vision.For this purpose, we used the fixation-offset paradigm and tracked eye-position using a high spatial and temporal resolution infrared eye-tracker.In addition, we performed a simulation with the same task in a group of five healthy controls.

View Article: PubMed Central - PubMed

Affiliation: Experimental Psychology, Helmholtz Institute, Utrecht University, Utrecht, The Netherlands; Autism Research Centre, Department of Psychiatry, University of Cambridge, Cambridge, United Kingdom.

ABSTRACT
Macular degeneration is the main cause for diminished visual acuity in the elderly. The juvenile form of macular degeneration has equally detrimental consequences on foveal vision. To compensate for loss of foveal vision most patients with macular degeneration adopt an eccentric preferred retinal location that takes over tasks normally performed by the healthy fovea. It is unclear however, whether the preferred retinal locus also develops properties typical for foveal vision. Here, we investigated whether the fixation characteristics of the preferred retinal locus resemble those of the healthy fovea. For this purpose, we used the fixation-offset paradigm and tracked eye-position using a high spatial and temporal resolution infrared eye-tracker. The fixation-offset paradigm measures release from fixation under different fixation conditions and has been shown useful to distinguish between foveal and non-foveal fixation. We measured eye-movements in nine healthy age-matched controls and five patients with juvenile macular degeneration. In addition, we performed a simulation with the same task in a group of five healthy controls. Our results show that the preferred retinal locus does not adopt a foveal type of fixation but instead drifts further away from its original fixation and has overall increased fixation instability. Furthermore, the fixation instability is most pronounced in low frequency eye-movements representing a slow drift from fixation. We argue that the increased fixation instability cannot be attributed to fixation under an unnatural angle. Instead, diminished visual acuity in the periphery causes reduced oculomotor control and results in increased fixation instability.

Show MeSH
Related in: MedlinePlus