Validity and Reliability of a Novel Ocular Pain Assessment Survey (OPAS) in Quantifying and Monitoring Corneal and Ocular Surface Pain

Abstract

Purpose: To validate the Ocular Pain Assessment Survey (OPAS), specifically designed to measure ocular pain and quality of life for use by eye care practitioners and researchers.

Design: A single-center cohort study was conducted among patients with and without corneal and ocular surface pain at initial and follow-up visits over a 6-month period. The content of the OPAS was guided by literature review, a body of experts, and incorporating conceptual frameworks from existing pain questionnaires. The Wong-Baker FACES Pain Rating Scale served as the gold standard for measuring the intensity of ocular pain.

Participants: A total of 102 patients aged 18 to 80 years completed the OPAS at the initial visit. A total of 21 patients were followed up after treatment.

Methods: Indices of validity and internal consistency (Spearman's rank-order, rs, or Pearson's correlation coefficients, rp), and coefficient of reliability (Cronbach's α) were determined in addition to equivalence testing, exploratory factor analysis (EFA), and diagnostic analysis.

Main outcome measures: Eye pain intensity was the primary outcome measure, and interference with quality of life (QoL), aggravating factors, associated factors, associated non-eye pain intensity, and self-reported symptomatic relief were the secondary outcome measures.

Results: The OPAS had criterion validity at both initial (rs = 0.71; n = 102; P < 0.01) and follow-up visits (rs = 0.97; n = 21; P < 0.01). Equivalence tests yielded OPAS and gold standard equivalence for both the initial and follow-up visits. The EFA supported 6 subscales (eye pain intensity at 24 hours and 2 weeks, non-eye pain intensity, QoL, aggravating factors, and associated factors) confirming multidimensionality. Cronbach's α >0.83 for all subscales established strong internal consistency, which correlated with the gold standard, including 24-hour eye pain intensity and QoL interference scores (rp = 0.81, 0.64, respectively P < 0.001). At follow-up, reduction in pain scores was accompanied by improvement in all dimensions of the OPAS. Percentage change in QoL correlated to percentage change in the gold standard (rp = 0.53; P < 0.05). The OPAS was sensitive (94%), specific (81%), and accurate (91%), with a diagnostic odds ratio >50.

Conclusions: The OPAS is a valid, reliable, and responsive tool with strong psychometric and diagnostic properties in the multidimensional quantification of corneal and ocular surface pain intensity, and QoL.

Conflict of interest statement

Financial interest: No conflicting relationship exists for any author.

Copyright © 2016 American Academy of Ophthalmology. Published by Elsevier Inc. All rights reserved.

Figures

Figure 1. Study design algorithm

Flow of the steps taken toward designing and validating the Ocular Pain Assessment Survey (OPAS). MEEI: Massachusetts Eye and Ear Infirmary, Boston, MA, USA.

Figure 2. Final design of the Ocular Pain Assessment Survey (OPAS) following factor analysis and validation studies

The boxed regions represent the gold standard method of quantifying pain intensity (Wong-Baker FACES Pain Rating Scale) against which the test numerical rating scales were validated, and the 6 factors (dimensions) of the OPAS comprising of test sub-scales that loaded onto each of the factors. Scores for each of the sub-scales were then followed as mean composite scores for each of the 6 factors, and monitored individually over time, generating both holistic and nuanced information. Symptomatic relief (Qs. 27 and 28) did not load onto any factors but was retained based on the physicians’ agreement that it formed an important question, which could be analyzed separately if needed.

Figure 3. Responsiveness of the OPAS

Dimension scores from the first follow-up visit post-treatment (n=21) were analyzed for determining responsiveness of the OPAS. Percent changes in mean scores showed that (A) there was reduction in eye pain intensity as measured by the gold standard (Gold Std) pain intensity scale (the Wong-Baker FACES® Pain Rating Scale) with improvement in all dimensions of the OPAS seen by concurrent reduction in mean dimension scores for eye pain intensity (past 24 hours), impact on quality of life (QoL), aggravating factors, associated symptoms and non-eye pain. (B) Detailed information was also retrieved by reviewing scores from individual test questions within each dimension. Within the dimensions of QoL and associated symptoms, sub-scale information regarding varying degrees of improvement in specific activities of daily life and eye-pain associated symptoms were also seen with reduction in eye pain intensity. Therefore, the OPAS in its entirety is responsive to changes across all dimensions.