The goal of this clinical study is to learn about the short-term physiological effects of low-dose atropine in healthy volunteers. The study seeks to examine three questions related to low-dose topically applied ophthalmic atropine:

1. Does applying two drops of 0.01% atropine sulfate solution cause the same clinical effects as one drop of 0.02% atropine?
2. How quickly do the pupil responses and accommodative amplitudes recover following a dose of 0.01% atropine, 0.02% atropine, and 0.05% atropine?
3. Does applying a single drop of 0.02% atropine sulfate solution cause the same clinical effects in participants with light vs. dark iris colors? Participants will have their pupil size and accommodative status measured at appropriate intervals to answer the questions above.

Inclusion Criteria:

1. Subjects may be male or female, of any race, and between 18-40 years old at the time of screening.
2. Patients must have best spectacle corrected visual acuity of at least 0.10 logMAR (20/25) in each eye.
3. Subjects must be willing and able to apply eye drops to their non-dominant eye and to return for all scheduled follow-up visits.

Exclusion Criteria:

1. Subjects with any contraindication to atropine use (as listed on package insert). At the time of this submission, the only contraindication listed is: "Hypersensitivity or allergic reaction to any ingredient in formulation"
2. Subjects using monamine oxidase inhibitors (MAOIs). These are: Isocarboxazid (Marplan), Phenelzine (Nardil), Selegiline (Emsam), and Tranylcypromine (Parnate).
3. Subjects with a history of any of the following medical conditions: collagen vascular disease, autoimmune disease, immunodeficiency diseases, ocular herpes zoster or simplex, endocrine disorders (including, but not limited to active thyroid disorders and diabetes), lupus, and rheumatoid arthritis.
4. Subjects with a history of intraocular or corneal surgery (including cataract extraction), active ophthalmic disease or abnormality (including but not limited to, blepharitis, recurrent corneal erosion, dry eye syndrome, neovascularization >1mm from limbus), clinically significant lens opacity, clinical evidence of trauma (including scarring). This includes any patient with open-angle glaucoma, regardless of medication regimen or control. Additionally, any patient with an intra-ocular pressure (IOP) greater than 21 mm Hg at baseline is specifically excluded from eligibility. Subjects with narrow angles (less than Van Herick angle of 3) will also be excluded.
5. Subjects who are pregnant, planning to become pregnant or breastfeeding during the course of the study.

All IPD variables, including data dictionaries, will be available to other researchers upon request to the principal investigator and completion of a signed data sharing agreement.

As this study is being registered retroactively (and the study is complete), all data can be made available upon request at this time (March 2026).

IPD can be accessed by emailing the PI who will make arrangements with appropriate UC Berkeley personnel to manage sharing.