Soaking hay helped my horse last spring with swollen lids and goopy eyes.  Either because it lowered his insulin and reduced his sensitivity to allergens, or because it prevented the dust in his hay from getting in to his eyes when eating from hay nets.  You could try wetting the hay to see if its dust.

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Kirsten and Shaku (IR) - 2019
Kitimat, BC, Canada
ECIR Group Moderator
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