Related Experiment Video
Updated: Jan 28, 2026

How to Study Placebo Responses in Motion Sickness with a Rotation Chair Paradigm in Healthy Participants
Published on: December 14, 2014
Ascorbic acid versus placebo in postoperative lid edema postphotorefractive keratectomy: A double-masked, randomized,
Aliagha Alishiri1, Seyed Aliasghar Mosavi2,3
1Department of Ophthalmology, Hormozgan University of Medical Sciences, Bandar Abbas, Iran.
Introduction:
Photorefractive keratectomy (PRK) is a proper type of refractive surgery used to remodel corneal stroma to compensate refractive errors. Corneal haze was reported as one of the side effects in several studies. This study was conducted for investigation of the effect of preventive effect of Vitamin C on eyelid edema, corneal haze, corneal epithelial healing, mitigation of pain, and epiphora.
Materials And Methods:
This study has been performed as a double-blind clinical trial on 51 patients who underwent PRK surgery. The patients were randomly divided into two groups as follows: case group who received oral ascorbic acid 250 mg once daily for 7 days and control group that took placebo 3 days before and 4 days after the surgical operation. The patients underwent a surgical operation on day 0. Then, the following factors were evaluated as the main outcome: postoperative lid edema, pain, corneal haze, and corneal reepithelialization.
Results:
The mean age of the patients was 28.52 ± 8.05 years. There was no statistically significant difference in the primary outcome of the subjective pain scores along with corneal haze and corneal reepithelialization between the treatment and placebo groups at any point during the postoperative period; however, there was a statistically significant difference and trend for lower lid edema in the ascorbic acids group on postoperative day 1 (P < 0.05).
Conclusion:
This study demonstrates that ascorbic acid may provide an alternative or add-on option for lid edema relief after PRK.
Related Concept Videos
The Placebo Effect
Polyprotic Acids
Bioequivalence Experimental Study Designs: Completely Randomized and Randomized Block Designs
Masking and Demasking Agents
There are many masking agents, such as cyanide, fluoride, triethanolamine, thiourea, and 2,3-bis(sulfanyl)propan-1-ol (formerly 2,3-dimercapto-1-propanol), with the masking agent chosen based on...
Administering Oxygen by Mask
Administering oxygen by mask is a common nursing intervention that provides supplemental oxygen to patients with respiratory distress or chronic lung conditions. This procedure involves delivering oxygen at a specified rate through a face mask connected to an oxygen source.
Equipment
The equipment necessary for this procedure includes:
Random Error

