Dry Eye Severity, Persistence Related to Neuropathic Pain
Dry Eye Severity, Persistence Related to Neuropathic Pain
The study population built on a cohort of male patients previously recruited from the Miami Veterans Affairs Medical Center for a study on the relationship between dry eye symptoms and systemic androgen levels. This cohort consisted of 263 patients with grossly normal eyelid, conjunctival and corneal anatomy. Exclusion criteria included age under 50 years, contact lens use, recent ocular surgery (<3 months), active anterior segment ocular disease other than dry eye (eg, keratitis) or a diagnosis of HIV, sarcoidosis, graft-versus host disease or any collagen vascular disease. Of the original 263 patients, we were able to recontact 102 members to re-evaluate their dry eye symptoms, as part of a quality improvement project. Of the 161 that were not recontacted, 13 had died, 14 had incorrect contact information, 109 could not be reached and 25 were not interested in participating. No differences in demographic information (age, race, ethnicity) were found between participants and non-participants. Miami VA Institution Review Board approval was obtained to perform a chart review and link patient data to the questionnaires. The study was conducted in accordance with the principles of the Declaration of Helsinki.
For each individual, we collected demographic information, pertinent history and medication information from the medical record. At the initial visit, all patients completed the DEQ5 and underwent an ocular surface examination. The ocular surface examination included measurement of tear osmolarity (TearLAB, San Diego, California, USA), tear break-up time, corneal staining (Oxford (Bron)), basal tear secretion test (Schirmer's strips with anaesthesia), and morphological and qualitative characterisation of the eyelid margin and meibomian glands. The DEQ5 was selected because its score combines patient responses regarding discomfort, dryness and tearing without considering visual function. The more commonly used Ocular Surface Disease Index, on the other hand, considers visual function and includes questions related to difficulty with reading, driving at night, working with a computer, and watching TV. Many of our patients seek eye care treatment for visual dysfunction, and on pilot testing, many had high Ocular Surface Disease Index scores for reasons other than dry eye.
The 102 patients that we could contact were again asked to complete the DEQ5 2–3 years later, along with the short-form McGill Pain Questionnaire (SF-MPQ) as it pertained to their ocular symptoms. The SF-MPQ is commonly used by pain specialists to characterise features of pain. The questionnaire consists of 15 words which include the sensory descriptors: throbbing, shooting, stabbing, sharp, cramping, gnawing, hot burning, aching, heavy, tender, splitting; and the affective descriptors: tiring exhausting, sickening, fearful and punishing cruel quantitatively scored from 0 (none) to 3 (severe). Patients were asked to apply these descriptors to their eye pain. The SF-MPQ was scored in three ways: an overall score, generated by summing responses to all 15 descriptors; a sensory score, calculated by summing responses to the sensory descriptors (1–11); and an affective score, calculated by summing responses to the affective descriptors (12–15). In addition, each descriptor of the SF-MPQ can be examined individually. Of note, hot burning is a classic descriptor of dysaesthesia and is the SF-MPQ descriptor most closely related to neuropathic pain. Patients were also asked about NOP symptoms of allodynia (eye pain caused or worsened by light (photoallodynia) and/or a change in temperature) and hyperalgesia (eye pain caused or worsened by wind).
The main outcome measure was the relationship between dry eye symptom severity and persistence (DEQ5) and additional measures of ocular pain (eg, SF-MPQ scores, NOP). Features of NOP were considered present if the patient (1) characterised the eye pain as hot burning, (2) reported symptoms of allodynia to light and/or change in temperature and/or (3) reported symptoms of hyperalgesia to wind.
All statistical analyses were performed using SPSS V.21.0 (SPSS, Chicago, Illinois, USA) statistical package. Frequencies and descriptive statistics were applied to the data, as appropriate. χ and Student's t tests (for normally distributed variables), and Mann-Whitney tests (for non-normally distributed variables) were applied (as appropriate) to compare categorical and continuous variables between subjects. Multivariable logistic regression analysis was used to determine factors that correlated with persistent dry eye symptoms over 2–3 years. This sample size was deemed appropriate to detect factors with moderate effect size, such as on symptom persistence (with a sample size of 102 patients and response probability of 15% and α=0.05, the power was greater than 90% to demonstrate effects of factors with OR ≥2.0 in a multiple logistic regression model for a variety of types of variables (ie, normally distributed continuous, dichotomous, ordinal)).
Methods
Study Population
The study population built on a cohort of male patients previously recruited from the Miami Veterans Affairs Medical Center for a study on the relationship between dry eye symptoms and systemic androgen levels. This cohort consisted of 263 patients with grossly normal eyelid, conjunctival and corneal anatomy. Exclusion criteria included age under 50 years, contact lens use, recent ocular surgery (<3 months), active anterior segment ocular disease other than dry eye (eg, keratitis) or a diagnosis of HIV, sarcoidosis, graft-versus host disease or any collagen vascular disease. Of the original 263 patients, we were able to recontact 102 members to re-evaluate their dry eye symptoms, as part of a quality improvement project. Of the 161 that were not recontacted, 13 had died, 14 had incorrect contact information, 109 could not be reached and 25 were not interested in participating. No differences in demographic information (age, race, ethnicity) were found between participants and non-participants. Miami VA Institution Review Board approval was obtained to perform a chart review and link patient data to the questionnaires. The study was conducted in accordance with the principles of the Declaration of Helsinki.
Data Collection
For each individual, we collected demographic information, pertinent history and medication information from the medical record. At the initial visit, all patients completed the DEQ5 and underwent an ocular surface examination. The ocular surface examination included measurement of tear osmolarity (TearLAB, San Diego, California, USA), tear break-up time, corneal staining (Oxford (Bron)), basal tear secretion test (Schirmer's strips with anaesthesia), and morphological and qualitative characterisation of the eyelid margin and meibomian glands. The DEQ5 was selected because its score combines patient responses regarding discomfort, dryness and tearing without considering visual function. The more commonly used Ocular Surface Disease Index, on the other hand, considers visual function and includes questions related to difficulty with reading, driving at night, working with a computer, and watching TV. Many of our patients seek eye care treatment for visual dysfunction, and on pilot testing, many had high Ocular Surface Disease Index scores for reasons other than dry eye.
The 102 patients that we could contact were again asked to complete the DEQ5 2–3 years later, along with the short-form McGill Pain Questionnaire (SF-MPQ) as it pertained to their ocular symptoms. The SF-MPQ is commonly used by pain specialists to characterise features of pain. The questionnaire consists of 15 words which include the sensory descriptors: throbbing, shooting, stabbing, sharp, cramping, gnawing, hot burning, aching, heavy, tender, splitting; and the affective descriptors: tiring exhausting, sickening, fearful and punishing cruel quantitatively scored from 0 (none) to 3 (severe). Patients were asked to apply these descriptors to their eye pain. The SF-MPQ was scored in three ways: an overall score, generated by summing responses to all 15 descriptors; a sensory score, calculated by summing responses to the sensory descriptors (1–11); and an affective score, calculated by summing responses to the affective descriptors (12–15). In addition, each descriptor of the SF-MPQ can be examined individually. Of note, hot burning is a classic descriptor of dysaesthesia and is the SF-MPQ descriptor most closely related to neuropathic pain. Patients were also asked about NOP symptoms of allodynia (eye pain caused or worsened by light (photoallodynia) and/or a change in temperature) and hyperalgesia (eye pain caused or worsened by wind).
Main Outcome Measures
The main outcome measure was the relationship between dry eye symptom severity and persistence (DEQ5) and additional measures of ocular pain (eg, SF-MPQ scores, NOP). Features of NOP were considered present if the patient (1) characterised the eye pain as hot burning, (2) reported symptoms of allodynia to light and/or change in temperature and/or (3) reported symptoms of hyperalgesia to wind.
Statistical Analysis
All statistical analyses were performed using SPSS V.21.0 (SPSS, Chicago, Illinois, USA) statistical package. Frequencies and descriptive statistics were applied to the data, as appropriate. χ and Student's t tests (for normally distributed variables), and Mann-Whitney tests (for non-normally distributed variables) were applied (as appropriate) to compare categorical and continuous variables between subjects. Multivariable logistic regression analysis was used to determine factors that correlated with persistent dry eye symptoms over 2–3 years. This sample size was deemed appropriate to detect factors with moderate effect size, such as on symptom persistence (with a sample size of 102 patients and response probability of 15% and α=0.05, the power was greater than 90% to demonstrate effects of factors with OR ≥2.0 in a multiple logistic regression model for a variety of types of variables (ie, normally distributed continuous, dichotomous, ordinal)).