Development and preliminary validation of a pain scale for ophthalmic pain in horses: The Equine Ophthalmic Pain Scale (EOPS).

This research aimed to create and test the validity of a new pain scale for assessing eye-related pain in horses. The new scale, called the Equine Ophthalmic Pain Scale (EOPS), scored behavioural, physiological, and eye-related indicators in horses with eye disorders and healthy horses. The scale was found to have high reliability and accuracy, but some items require improvement.

Development and Purpose of Equine Ophthalmic Pain Scale (EOPS)

• The researchers worked to develop a new pain scale to assess ocular, or eye-related, pain in horses, known as the Equine Ophthalmic Pain Scale (EOPS).
• The primary objective of this study was to create this scale and initially validate its effectiveness.
• Various indicators associated with ocular pain were selected, which were categorised as behavioural, physiological, or ocular expressions.

Methodology of the Research Study

• Eight horses with diagnosed eye or adnexa (supporting) diseases requiring medical or surgical treatment were part of the initial group (group P).
• The EOPS was applied to this group P at the start (T0) and 1 week later (T7).
• Also, 15 healthy horses were selected as a control group (group C), and the EOPS was applied to them twice, with a week gap.
• The assessments were recorded on video, which were later analysed by seven masked observers who scored the items falling under the behavioural and ocular expression categories of the EOPS.

Results and Findings

• The inter- and intra-observer reliability for most scored items was excellent, with intraclass correlation coefficients equal to or above 0.75.
• Cronbach’s alpha, a measure of internal consistency, for the EOPS was 0.76, suggesting a good internal consistency for EOPS.
• The total score (TS), which was a sum of all scores, differed significantly between the control and pathology group at T0, indicating the scale’s ability to distinguish between healthy and afflicted subjects.
• The score reduced after treatment in group P, indicating that the EOPS was responsive to changes in condition.
• The ‘area under the curve’ (AUC) was 0.918, within a 95% confidence interval of 0.815 – 1.000, illustrating high accuracy in distinguishing between healthy and pathological animals.
• The sensitivity and specificity of EOPS at the optimal cut-off (TS≥ 7) were found to be 81.3% and 100% respectively, indicating a high degree of accuracy in identifying horses with eye-related pathology.

Potential for Improvement

• Despite promising results, certain items like ‘overall behaviour’, ‘position inside the box’, ‘ear movements’ and ‘head position’ along with physiological parameters, didn’t demonstrate optimal reliability, internal consistency and correlation with total item score.
• This indicates potential for further refinement of this composite scale.