Convergence Insufficiency Symptom Survey (CISS)

What convergence insufficiency is

When you look at a book, a phone or any other near object, both eyes have to turn inwards at the same time so that the two separate images can be combined into one clear image. That inward turning is called convergence. It is part of how the two eyes work together, and it has to keep working as reading distance, reading time and attention change.

Convergence insufficiency means that the inward turning is not strong enough, or that it can be achieved at first but not sustained. Some people feel fine when they start reading, but after a while their eyes tire, the text seems to move, they lose their place, or they have to go back and read the same line again. These sensations are often more noticeable during long reading sessions, homework, or extended computer and phone use.

Convergence insufficiency is not a refractive problem such as short-sightedness, long-sightedness or astigmatism. A refractive prescription describes how the eye focuses an image; convergence describes whether the two eyes can coordinate on the same near target. The two can occur together or separately, so an ordinary pair of prescription glasses alone usually does not improve convergence itself. Treating every blurred or tiring experience as a wrong prescription makes it easy to miss which visual function actually needs to be clarified.

That said, having these symptoms does not necessarily mean convergence insufficiency is present. Discomfort during close work has several possible causes, and your own impressions alone rarely separate them. If symptoms keep returning and affect reading or work, a more useful approach is to write down the situations in which they occur, how long they last and how much they bother you, and bring that to a professional.

What the age-specific cutoffs mean

The CISS is a questionnaire about symptoms during close work. It measures how much those symptoms bother you. It is not a diagnostic tool, and it is not an instrument that measures how the eyes function. Every question asks how reading or near work feels, and a higher total means the respondent reports a higher level of symptom burden.

This page uses different cutoffs by age: 16 for people under 18, from the CITT (Convergence Insufficiency Treatment Trial) research for ages 9 to 18; and 21 for people aged 18 and over, from validity research on the adult CISS. Reaching the applicable cutoff means the symptom burden is worth a full examination; it does not mean the questionnaire has made a diagnosis.

A high score does not necessarily mean convergence insufficiency. Accommodative dysfunction, dry eye and an uncorrected refractive error can all produce similar symptoms at near: tiring easily, blur, reduced concentration or the need to reread. Telling these apart requires an actual examination, not a questionnaire. Conversely, a score below the cutoff cannot be used to rule out every visual problem.

So the most useful way to read your score is as a clue for arranging the next step, not as a label to give yourself. Notice which questions you repeatedly score highly on, for example blurred text, double vision, eye strain, or losing your place. That kind of specific detail helps the conversation during a full examination.

• A CISS score reflects symptom burden, not a diagnosis.
• The cutoff is 16 for people under 18 and 21 for people aged 18 and over.
• At or above the cutoff, arrange a full examination rather than deciding the cause yourself.

What to do when the score is high

If your score reaches the cutoff for your age group (16 if you are under 18; 21 if you are 18 or over), or if discomfort during close reading keeps affecting daily life even when the score is not high, you can ask an optometrist or ophthalmologist to arrange a full binocular vision examination. Alongside the CISS score, it helps to describe whether symptoms appear while reading, doing homework, using a screen or in other situations, and roughly how long it takes before the discomfort starts.

A full examination usually assesses the near point of convergence, that is, how close a target can come while a single image is still maintained. It may also assess fusional vergence ranges, to understand how well the two eyes coordinate while holding a single image, and accommodation, to see how the eyes adjust clarity between different near focal distances. Which tests are performed and how they are interpreted is decided by the professional according to the individual.

Before the examination is complete, do not infer the cause of your symptoms yourself, and do not act on the questionnaire score alone. The role of the questionnaire is to help you recognise what is bothering you and to raise the need for an examination; the actual cause and the next step should be explained by a professional based on a full examination.