The interaction between homatropine and optical blur on choroidal thickness

Area of Science:

• Ophthalmology
• Physiological Optics
• Pharmacology

Background:

• Choroidal thickness plays a role in emmetropization and myopia progression.
• Muscarinic antagonists like homatropine are used in managing refractive errors.
• Understanding the interplay between optical defocus and pharmacological agents is crucial for eye health.

Purpose of the Study:

• To investigate the short-term effects of myopic and hyperopic defocus, combined with homatropine, on choroidal thickness and ocular biometry.
• To determine if homatropine modulates the ocular response to different types of defocus.

Main Methods:

• Thirty young adults (myopes and emmetropes) underwent measurements of subfoveal choroidal thickness and ocular biometry.
• Participants were exposed to monocular optical blur (+3.00 D, -3.00 D, or 0.00 D) combined with either 2% homatropine or placebo.
• Measurements were taken at baseline, 30 minutes, and 60 minutes post-intervention, with conditions tested in a randomized order.

Main Results:

• Hyperopic defocus (-3.00 D) with placebo caused significant choroidal thinning.
• Homatropine prevented this thinning response to hyperopic defocus.
• Myopic defocus (+3.00 D) induced significant choroidal thickening with both placebo and homatropine; homatropine alone also increased choroidal thickness.
• Axial length changes were observed, generally opposite in direction to choroidal thickness changes.

Conclusions:

• Homatropine effectively blocks the choroidal thinning induced by hyperopic defocus.
• Homatropine did not enhance the choroidal thickening effect of myopic defocus.
• The differential effects suggest distinct ocular pathways for responding to myopic versus hyperopic blur, or a limit to the choroid's thickening capacity.