Background
A decrease in ocular surface temperature (OST) can cause a perceived sensation of dryness and promote the basal secretion of tear fluid. Therefore, OST is an important physiological parameter for maintaining ocular surface homeostasis and has also been used as an indicator of dry eye, a condition where dryness is the main complaint.
Tear film instability tends to decrease OST, while inflammation tends to increase it owing to the increased friction between the ocular surface and the eyelid. The most common method for clinically assessing inflammation is to evaluate hyperaemia qualitatively by grade; however, recently, a method has been developed to assess red blood cell movement as blood flow.
When wearing a soft contact lens (SCL), the tear film is divided into pre- and post-lens tear films. This can lead to an instable pre-lens tear film because the tear film thickness is thin. The dryness sensation experienced by SCL wearers is thought to be caused by an unstable tear film and friction between the SCL and the ocular surface. However, the relationship between OST, conjunctival blood flow (CBF) and dryness is unknown.
What was the aim of your study?
This study aimed to investigate the association between dryness, OST, and CBF after wearing two types of SCLs following airflow stimulation, which increases the dryness sensation. Additionally, the study compared OST and CBF between the two types of contact lenses.
What do the results of the study show and why might they be relevant to eye care practitioners?
A total of 21 SCL wearers were recruited, the participants used two different types of SCLs. Measurements were taken over four days. Excluding the first day, on three of the four days, OST, CBF, tear meniscus height (TMH), non-invasive tear film stability (NIBUT), and visual analog scale (VAS) scores were recorded after airflow stimulation.
The measurements were conducted without SCLs on the first and second days and with different SCLs on the third and fourth days. Results indicated that, when wearing SCLs, dryness was significantly but weakly correlated with OST (r = -0.375, p < 0.05) and CBF (r = 0.339, p < 0.05) (figures 1 and 2).
This study demonstrated that SCL wearers who perceive dryness sensation when wearing SCL exhibit decreased OST, suggesting unstable tear film stability and increased CBF, indicating subclinical inflammation.
Additionally, we found that by changing the type of contact lens used, the dryness was reduced and OST and CBF were altered. Therefore, if an SCL wearer experiences dryness, they should change to an SCL with improved wettability properties.
What are the limitations of the work?
This study has some limitations. First, while we added airflow stimulation to better evaluate the dryness sensation, we did not evaluate OST and CBF prior to this stimulation.
Second, although we found a correlation between dryness sensation, OST and CBF, we did not recruit SCL wearers with severe dryness sensations. This was because these subjects could have potentially experienced severe inflammation. Thus, the association we found could have changed if we had recruited SCL wearers with a severe degree of dryness.
What further work still needs to be undertaken in this field?
Future studies should determine the differences in these parameters before and after airflow stimulation to better understand the effects of airflow. Moreover, it is essential to investigate the association between dryness sensation, OST and CBF in patients with dry eyes or SCL wearers with severe contact lens discomfort.
Conclusion
Dryness experienced when wearing SCLs after airflow stimulation correlated with OST and CBF, indicating that when dryness was high, OST was low and CBF was high. These results suggest that OST and CBF assessments can be used to evaluate dryness sensation.
- Takashi Itokawa is a certified orthoptist at Toho University and focuses on ophthalmic examination tasks. He obtained his Ph.D. from Toho University and has published over 20 papers to date. His main research fields include dry eyes and contact lenses, with a particular focus on the stability of the tear film and the temperature and blood flow of the ocular surface.
- Full findings were published in: Itokawa T, Okajima Y, Iwashita H, Koji K, Tashiro S, Suzuki T, Hori Y. Association between dryness sensation and ocular surface temperature and conjunctival blood flow in soft contact lens wearers. Cont Lens Anterior Eye. 2024 Jun;47(3):102166. doi: 10.1016/j.clae.2024.102166. Epub 2024 Apr 11