The purpose of this Phase 2a study is to assess changes in tear volume by the non-invasive techniques Ultra High Resolution Optical Coherence Tomography (UHR-OCT) following the administration of P-321 Ophthalmic Solution or Placebo in subjects with tear deficient dry eye disease.

This is a single-center, randomized, cross-over placebo controlled study to evaluate the changes in tear volume by P-321 Ophthalmic Solution and Placebo. The study will enroll subjects with tear deficient dry eye disease to receive sequentially one of two treatment sequences: P-321 Ophthalmic Solution then Placebo or Placebo then P-321. The study will consist of two Phases: In each Phase, subjects will be treated with P-321 Ophthalmic Solution under the same study design.

Approximately twenty-four eligible subjects will complete the study with approximately 8 subjects participating in Phase 1 and the remainder of the 24 subjects participating in the phase 2. Decisions on the dose to be used in Phase 2 will be made based on Phase 1 data.

The study will consist of three study visits: a Screening Visit (Visit 1), and two treatment visits (Visit 2 and Visit 3). The primary and secondary outcome measures will be assessed at each treatment visit. Safety assessments include adverse events (AEs).

Inclusion Criteria:

1. Provide written informed consent

2. Male or female subjects aged 18 to 80 years

3. Have a history of predominantly tear-deficient dry eye of mild to moderate severity, supported by a previous clinical diagnosis

4. Have normal lid anatomy

5. Subjects must:

   1. Remain on current medications for the duration of the study and have been on the current medication regimen at least during the past 28 days

Exclusion Criteria:

1. Have undergone refractive eye surgery in either eye during the past 12 months
2. Have undergone uncomplicated cataract surgery in either eye during the past 3 months
3. Have undergone previous eyelid surgery in either eye (External blepharoplasty, not resulting in exposure or abnormal blinking is allowed)
4. Have undergone botulinum toxin (BotoxTh1 or equivalent) injection in the periocular area within 3 months prior to Visit 1
5. Subjects that have a systemic, multi-organ disease requiring active medical or surgical treatment are excluded with the exception of subjects with SS or GVHD
6. Have punctal plugs, punctal occlusion, history of nasolacrimal duct obstruction or wear scleral lens.
7. Past or present exposure keratopathy, neurotrophic keratopathy, lagophthalmos, or trichiasis

Only one patient was enrolled in the study, the patient was randomized into the Group of P-321 Ophthalmic Solution Then Placebo Comparator. No patients participated in the Group of Placebo Comparator Then P-321 Ophthalmic Solution

Subjects were to receive 2 treatments (P-321 Ophthalmic Solution and Placebo) during this study; first treatment on Visit 2 (3 to 9 days after screening) and second treatment on Visit 3 (7 to 14 days after the first treatment).

An AE was defined as any untoward medical occurrence in a subject or clinical investigation subject administered a pharmaceutical product, which did not necessarily have to have a causal relationship with this treatment. A treatment-emergent AE (TEAE) was an AE that either commenced following initiation of study treatment or was present prior to study treatment but increased in frequency or severity following initiation of study treatment.