Corneal mechanical sensitivity in people with chronic pain
This article has been reviewed by Brandon Baksh, BA, and Anat Galor, MD, MSPH
Chronic pain is a common and often debilitating condition. Chronic pain syndromes can be localized to the head and face and involve the trigeminal system, for example in migraine and trigeminal neuralgia, explained Brandon Baksh, BA.
He went on to say that chronic pain syndromes can also be prevalent, such as in fibromyalgia, or localized outside of the head and face, such as back pain, and that nerve abnormalities have been linked to the syndromes. chronic pain.
“As eye care providers,” he said, “we can assess this link between nerve abnormalities and chronic pain.”
He pointed out that corneal sensitivity can be measured in the office.
Goal of the study
Corneal sensitivity is impaired in several eye conditions. However, its relationship to chronic pain conditions outside the eye is unclear.
To learn more about the impact of chronic pain outside the eye on corneal sensitivity, the authors investigated whether people with chronic trigeminal pain had differences in corneal sensitivity compared to people with pain. chronic non-localized in the trigeminal system.
Their hypothesis was that patients with chronic trigeminal pain have differences in corneal mechanical detection threshold compared to those with chronic pain that is not localized in the trigeminal system.
A cross-sectional study was conducted with South Florida veterans with chronic pain (duration> 3 months) seen in an eye clinic.
The main independent variables were the diagnoses and locations of pain, as recorded by participants in a survey.
The main dependent variable was the mechanical detection threshold of the cornea, which was assessed using a modified Belmonte esthesiometer.
To assess confounding variables, data were collected on demographics, dry eye symptoms and signs, mental health indices, systemic comorbidities, and quality of life indices.
Individuals were divided into two groups based on their pain diagnosis:
· Group 1 (trigeminal pain) – chronic painful conditions involving the trigeminal system
- Burning mouth syndrome
- Trigeminal neuralgia
- Trigemino-mandibular disorder (TMD)
· Group 2 (Other pain) – chronic painful conditions that do not localize in the trigeminal system
Corneal mechanical threshold assessment
The corneal mechanical threshold was assessed with a modified Belmonte esthesiometer:
- Pulses of air at room temperature were used on the right eye.
- Started at 10ml / min and waited 15 seconds between pulses
- Increase by 10 ml / min, until the patient can feel the pulse
- This was repeated a 2nd time and the average was used
- If the difference between the 2 trials was> 20, a 3rd reading was taken
Baksh noted that a lower detection limit using the Belmonte Esthesiometer meant higher corneal sensitivity.
Continuous variables were assessed using the independent t test. Correlations were assessed using Pearson’s r coefficient and categorical variables were assessed using the Chi-square test.
All reported p-values are two-tailed and p
This study included 568 people with one or more chronic painful conditions. The mean age was 61 ± 10.5 years. 89% were male, 44% identified as white, and 25% identified as Hispanic.
The mean corneal mechanical detection threshold was 81 ± 38 ml / min, with a range of 10 to 240 ml / min.
The authors found that the Trigeminal Pain group (n = 122) had a lower mean corneal mechanical detection threshold (i.e., higher sensitivity) (73 +/- 31) compared to the Other Pain group ( n = 446, mean threshold 84 +/- 40). This was statistically significant.
The authors also evaluated continuous variables. Variables that were found to be significantly correlated with a lower corneal mechanical detection threshold (higher sensitivity) included a high depression score, a high PTSD score, more severe dry eye symptoms, more severe eye pain, as well as ‘poorer quality of life, lower age, lower cholesterol and triglyceride levels.
A lower corneal mechanical detection threshold (higher sensitivity) may be associated with pain phenotypes such as the presence of chronic pain involving the trigeminal system, 5 or more pain conditions, and the presence of arthritis.
Beyond pain phenotypes, other factors that may play a role include a higher depression score, black race, dyslipidemia, and use of CPAP.
Brandon Baksh, BA
This article is based on Baksh’s presentation at the ARVO 2021 Virtual Annual Meeting. Baksh has no financial disclosure.