The objectives of this study are:

• To assess the effect of ophthalmic phentolamine mesylate in mesopic conditions on the four endpoints:

  1. Contrast sensitivity
  2. Low contrast visual acuity
  3. Wavefront aberrometry
  4. Subjective questionnaire

• To assess the safety of ophthalmic phentolamine mesylate

Double-masked, placebo-controlled, single-dose Phase 2 study in 24 patients experiencing severe night vision difficulties to evaluate ocular and systemic safety and efficacy following administration of one drop of phentolamine mesylate 1.0% QD in each eye for 1 day.

Inclusion Criteria:

1. Male or female patients ≥ 18 years of age
2. Currently experiencing severe night vision difficulty as reported subjectively
3. At least two patches below the normal range at any two frequencies in Contrast Sensitivity done under mesopic conditions with glare
4. Improvement in low contrast visual acuity (LCVA) in dim light during illumination of contralateral eye
5. Good general health
6. Written informed consent to participate in this trial
7. Ability to comply with all protocol mandated procedures and to attend all scheduled office visits

Exclusion Criteria:

1. Patients with untreated cataracts grades 1-4
2. Patients who wear contact lenses
3. Less than 5 weeks post-refractive surgery (LASIK or PRK)
4. Less than 5 weeks post intraocular lens insertion
5. Low blood pressure (systolic <120 mm Hg or diastolic <80 mm Hg)
6. A history of heart rate abnormalities
7. Administration of any investigational drug within 30 days of study initiation
8. Use of any eye drops with a pharmacologic effect on the pupil within 7 days of Visit 1
9. Use of any systemic alpha adrenergic antagonists (Appendix 1)
10. Known local or systemic hypersensitivity to adrenergic antagonists
11. For women of childbearing potential: currently pregnant or lactating, or unwilling to use birth control during the study