To Compare Home Vision Therapy and Prism Prescription in Presbyopic Persons With Convergence Insufficiency

Between non-strabismic binocular vision problems, convergence insufficiency is the most common problem (6) even in people with presbyopia this problem has high prevalence. (11) The most common ocular finding in these patients is an increase in near exophoria and thus reduces person's performance in activities such as reading, computer working and near activities. (12) Despite the effectiveness of vision therapy in reducing patients' symptoms and improving visual function, the different accommodation and vergence systems in the elderly may cause different results (1) so a comprehensive study of adult patients over the age of 40 with convergence insufficiency is needed. According to our knowledge the only study in these patients was done by MH Birnbaum (13) in 1999 which had several limitations. For example, in their study, the results were classified and recorded as success and failure in functional therapy and improvement or non-improvement of asthenopia; Success in treatment was achieved when two criteria were met: 1. The criterion of asthenopia includes achieving the ability to study for at least one hour without diplopia; And the ability to study without headache, eye pain and loss of concentration at least 75% of the time 2- Achieving 3 options of functional criteria including having an appropriate near point of convergence, having appropriate near point of convergence with red lens, having low near phoria and positive fusional vergence.

Another problem of this study was: not using the CISS questionnaire, which is a valid questionnaire of convergence insufficiency, and only considered success in treatment based on the two criteria, it should be mentioned that in their study the method for patients' selection did not report; On the other hand, the study was not blind, the importance of designing blind studies has been proven. Only one study by B Teitelbaum assessed prism prescription in patients over 40 years with convergence insufficiency (14) their study had two main problems, first: selected patients did not necessarily have convergence insufficiency, because the two basic criteria for convergence insufficiency (near point of convergence and positive fusion vergence) did not include in their study. Second: not using commercial progressive add lenses in patients glasses and it was unique lens with special design with limitation in base in prism prescription.

Because of the effects of various factors on vision therapy including patients' motivation, lack of cooperation in eye exercise, inappropriate age and unfavorable economic conditions, (especially in developing countries like Iran) or pandemic condition like COVID19 pandemy, vision therapy may not always be possible (1-3) and clinicians may have to prescribe base in prism for these patients. On the other hand, due to the changes in accommodation and convergence system and their interaction with aging (1, 3-4) study of their responses to the two types of treatments including active vision therapy and passive base in prism therapy and comparing them are noticeable matter and solving this challenge is absolutely necessary.

This study includes two phases. In the first phase, investigators will evaluate the reliability and validity of the Persian version of questionnaire for the elderly patients, this version was validated for young patients (38). Investigators will modify this questioner for presbyopic patients. For this purpose, six optometrists experienced in binocular vision will assess the questioner in two aspects: validity and reliability.

The validity of the modified Persian CISS include face validity (use of meaningful words), content validity (relevancy, clarity, comprehensiveness), discriminant validity Using a 6-point Likert scale (very weak, weak, moderate, good, very good, best), face validity will be assessed according to the aspects of fluency in elderly patients' cultural acceptance in iran and a score of ≥4 for each question will be passable. Content validity will be determined based on 1-relevancy (the extent to which the question of interest can being closely connected or appropriate for characteristics of the content under study), 2-clarity (appropriateness of the selected items in terms of being coherent and intelligible in concept and writing style), and 3-comprehensiveness (the ability of the questioner to cover all domains related to the topic under study). Relevancy and clarity will be assessed item by item and for the whole items in the questioners using a 4-point Likert scale (1-undesirable, 2-relatively desirable, 3-desirable, 4-completely desirable), and the Item Content Validity Index (I-CVI) and Scale Content Validity Index (S-CVI) will be calculated for the indices. Universal agreement approach will be used to check, the I-CVI value and it will be between 0-100%, and I-CVI≥ 0.8 will be considered passable. 20 The S-CVI for relevancy and clarity will be determined by averaging all I-CVI values. Comprehensiveness will be only measured at the scale level using a 4-point Likert scale (1- incomprehensive, 2- relatively comprehensive, 3- comprehensive, and 4- totally comprehensive). Then, the reliability of the questionnaire will be assessed using test-retest reliability analysis between first and second questioner administration in a group of 50 presbyopic patients aged 40-60 with convergence insufficiency. The elderly participants will be asked to participate in a second administration of the questionnaire 7-14 days later. To assess discriminant validity, convergence insufficiency will be categorized to 3 groups of mild (PFV ≥1.50 × near exophoria), severe (PFV < near exophoria), and moderate (values in between these groups) based on the severity of clinical manifestations according to the Convergence Insufficiency Treatment Trial guideline, and the mean overall CISS score Will be compared between these three groups.