What causes conjunctival injection and erythema (redness) when a patient is in a lateral decubitus position?

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From the Guidelines

To alleviate bloodshot and red eyes when lying in a lateral position, it is crucial to reduce pressure on the eyes and ensure proper lubrication, as evidenced by studies on corneal injuries and eye protection during anesthesia 1. When lying on your side, the eye in contact with the pillow or surface may experience increased pressure, leading to temporary blood vessel dilation and redness. To address this issue, consider the following measures:

  • Change your sleeping position to your back to minimize pressure on your eyes.
  • Use a softer pillow or elevate your head slightly to reduce pressure on your eyes.
  • Utilize artificial tears like Refresh or Systane to help if dryness is contributing to the redness; use 1-2 drops in each eye before bed and upon waking.
  • If you must sleep on your side, consider a contoured pillow that reduces eye pressure. Studies such as those by Grover et al. 1 have shown that patient position can affect the incidence of corneal injuries, with the lateral decubitus position being associated with a higher incidence of corneal injury compared to the dorsal decubitus position. It is essential to note that while this condition is typically harmless, if it persists or is accompanied by pain, vision changes, or discharge, consulting an eye doctor is necessary as it could indicate an underlying condition like glaucoma or dry eye syndrome 1. The redness occurs because blood vessels in the conjunctiva (the clear membrane covering the eye) dilate when compressed, becoming more visible against the white sclera, as observed in studies on corneal injuries and eye protection during anesthesia 1.

From the Research

Possible Causes of Bloodshot Eyes in Lateral Position

  • Red eye, also known as conjunctival injection, can be caused by various factors such as dryness, allergy, visual fatigue, contact lens overwear, and local infections 2.
  • In patients with open-angle glaucoma, lying in a lateral decubitus posture can increase intraocular pressure (IOP) in the dependent eye, which may lead to bloodshot eyes 3.
  • Systemic diseases can also cause red eye, and it is essential to inspect the external eye and check for warning signs such as pain, loss of corneal transparency, and reduced visual acuity 4.

Effects of Lateral Position on Intraocular Pressure

  • Studies have shown that IOP is higher in the dependent eye than in the nondependent eye in lateral decubitus posture, regardless of head position 3.
  • Lower head position can increase IOP in the dependent eye, and adjusting the height of a pillow may help mitigate IOP elevations in glaucoma patients 3.

Treatment and Management

  • Artificial tears can help relieve symptoms of dry eye and improve automated visual field testing in patients with glaucoma and dry eye syndrome 5.
  • Oral antihistamines such as diphenhydramine can decrease tear volume, while loratadine has minimal effects on tear volume, tear stability, and intraocular pressure 6.

References

Guideline

Guideline Directed Topic Overview

Dr.Oracle Medical Advisory Board & Editors, 2025

Research

Ocular Emergencies: Red Eye.

The Medical clinics of North America, 2017

Research

The red eye.

European journal of ophthalmology, 2021

Research

Effect of artificial tears on automated visual field testing in patients with glaucoma and dry eye.

Canadian journal of ophthalmology. Journal canadien d'ophtalmologie, 2013

Professional Medical Disclaimer

This information is intended for healthcare professionals. Any medical decision-making should rely on clinical judgment and independently verified information. The content provided herein does not replace professional discretion and should be considered supplementary to established clinical guidelines. Healthcare providers should verify all information against primary literature and current practice standards before application in patient care. Dr.Oracle assumes no liability for clinical decisions based on this content.

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