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G. T. Timberlake, S. A. Grose, J. H. Maino; Preferred Retinal Locus (PRL) - Hand Coordination in Fine Manual Tasks. Invest. Ophthalmol. Vis. Sci. 2007;48(13):3547.
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Individuals with central scotomas from macular degeneration have difficulties performing fine manual tasks, but the visuomotor basis of this impairment has not been investigated. Our goal is to characterize manual manipulation by measuring spatial-temporal relationships of the PRL, scotoma, and objects when subjects with central scotomas perform fine manual tasks requiring eye-hand coordination.Method. We developed a technique that enables a subject to see his hand and objects in a scanning laser ophthalmoscope (SLO) while he manipulates the objects. The resulting SLO images show a subject’s hand and objects on the retina while the subject inspects and manipulates them (inset image). Two visually normal subjects and one with a central scotoma (PRL 9.8° visually below foveal position, acuity 0.9 log MAR) performed three tasks: duplicating a model pattern of pegs (inset), tracing an ellipse with the index finger, and tapping target objects in sequence. Positions of the fingers, PRL (or fovea) and objects were measured from recorded SLO images.
The temporal pattern of PRL-finger movement was similar to fovea-finger movements, but the scotoma subject took longer to perform each task and made more errors. Peg pattern duplication took 68 sec for the scotoma subject compared to 14 sec for the normal subjects. Cross correlation analysis showed that finger position lagged PRL position 0.8 sec for the scotoma subject and foveal position 0.3 sec for normal subjects. Portions of the pegs, ellipses, and tapping targets were in scotomatous retina 80-94% of the time and the fingers 19-33% of the time. In terms of errors, the scotoma subject’s fingers were off the ellipse 87% of the time compared to 15% for normals and missed the tapping target 70% of the time compared to 11% for normals.
Our technique allows investigation of fine eye-hand manipulation without the need to calibrate eye tracking devices and coordinate them with hand position measurements. Preliminary measurements suggest that scotomas often obscure target objects and fingers, adversely affecting the ability to perform fine manual tasks.
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