An enhanced model for environmental dry eye: Exploring pathological features and underlying factors

This study aimed to develop an enhanced environmental dry eye (EDE) model that accurately reproduces the etiology of prolonged visual fatigue and investigates the underlying pathological features. A total of 40 adult SPF-grade Wistar rats were randomly assigned to control (n = 20) and model (n = 20) groups. Rats in the control group were maintained under normal conditions, while rats in the model group were exposed to a controlled frontal airflow of 2-4 m/s from a fan for 7.5 h daily while placed on a suspended cylindrical wire mesh frame. Various assessments were performed at different time points during the 14-day experiment, including blink frequency, tear secretion (phenol red thread test), tear film breakup time (BUT), fluorescein staining (FL), corneal epithelial status (light microscopy), ultrastructure of corneal epithelial cells (electron microscopy), and expression levels of inflammatory cytokines (IL-1β, TNF-α) in tears (enzyme-linked immunosorbent assay). Additionally, mRNA and protein expression levels of MMP-9, IL1β, IL6, TNF-α, IFN-γ, and caspase-3 in corneal tissues were quantified (real-time quantitative PCR and Western blotting). Compared to the control group, the model group rats exhibited significant decreases in blink frequency (P < 0.001), tear secretion (Schirmer I test) values (P < 0.001), and tear film breakup time levels (P < 0.001). There was also a significant increase in fluorescein staining scores (P < 0.001) in the model group. Histological examination revealed distinct differences of the corneal epithelium between groups. The corneal epithelium of the model group appeared thicker, with disorganized cell arrangement in the superficial and basal layers, partial defects or detachment of superficial epithelial cells, and a rough, uneven surface. Scanning electron microscopy observations showed a rough corneal epithelial surface with numerous cracks and scattered vesicular-like structures in the model group. Furthermore, the model group rats exhibited a significant increase in expression of IL-1β and TNF-α in tears (P < 0.001), and upregulated expression levels of MMP-9, TNF-α, IL-1β, caspase-3, IL-6, and IFN-γ at both the mRNA and protein levels in corneal tissues (P < 0.001). In conclusion, the modified "wire-meshing cylindrical board" model effectively overcomes the limitations of the traditional "jogging board " dry eye model and successfully simulates the etiology of prolonged visual fatigue. This innovative EDE model demonstrates a high degree of relevance to dry eye conditions resulting from prolonged visual tasks, with a high success rate of model induction. Moreover, it proves to be a simple, practical, and easily replicable model, making it highly suitable for further studies on prolonged visual fatigue and facilitating its widespread adoption in research and clinical applications.

Susceptibility to induced visual discomfort during the menstrual cycle while viewing a visual display unit

PURPOSE

Consistent variations in reports of visual discomfort during the female menstrual cycle are found when virtual reality headsets are used to display moving images. Because little is known about the influence of this cycle on susceptibility to visual discomfort in other situations, we performed a laboratory study using an intensive visual task.

METHODS

Twelve female participants, with normal-length menstrual cycles, completed the study. This required them to play a computer game for 30 minutes while viewing the screen through -2.00-D lenses. Questionnaires were used to record symptom changes; visual acuity and near points of accommodation (NPA) and convergence (NPC) were also recorded both before and after the game. The participants performed this task on designated days (5, 12, 19, and 26) of their menstrual cycle chosen because they fall in line with peaks and troughs of ovarian hormone levels. Cycle phase was confirmed by the measurement of salivary estradiol and progesterone levels.

RESULTS

The task performed produced clear changes in all metrics examined. Visual discomfort first increased, on average, after 6 minutes; VA declined on average by 0.02 logarithm of the minimum angle of resolution and NPC and NPA both receded by just over 1 cm. However, none of these changes differed significantly at any stage of the menstrual cycle.

CONCLUSIONS

We conclude that visual discomfort, generated by providing increased accommodative demand while viewing a visual display unit, does not vary significantly during the menstrual cycle.