What is Near Point of Convergence (NPC)?
Near Point of Convergence (NPC) is the closest distance from a person’s face at which their two eyes can still work together to keep a single, focused image before one eye loses its lock and vision splits into two.
It’s a simple test that tells clinicians how well a patient’s two eyes work together at close range. This measurement is a key part of any binocular vision assessment. It’s especially useful for patients reporting eyestrain, headaches, or difficulty reading.
How is Near Point of Convergence Measured?
The test involves moving a small target slowly along the midline towards the patient’s nose and watching carefully for two things.
The first is the break point: the moment at which the eyes can no longer hold fusion together and one eye deviates outward, or the patient reports seeing double. The second is the recovery point: the target is drawn back until the patient re-establishes single vision, which tells the clinician how readily the convergence system can reassert itself once it has failed.
In UK optometric practice, the standard tool for recording both values is the RAF rule (Royal Air Force near point rule), a calibrated rod that provides a standardised scale for measuring the distances in centimetres.
What the patient is asked to look at makes a meaningful difference to the outcome. Routine testing typically uses an accommodative target such as small print, which engages both the focusing and convergence systems simultaneously. When the aim is specifically to identify convergence insufficiency, a penlight paired with red-green glasses is more sensitive. It strips away the accommodative stimulus and tests the vergence system in isolation, often revealing a receded NPC that a standard target might miss.
Repeating the test increases its diagnostic sensitivity, since NPC values can shift with fatigue over successive attempts. A noticeably wider gap between an early and later reading can itself point to a problem.
What is a Normal NPC Value?
Clinically, a break point of 6 cm or less from the nose is generally considered normal, with a recovery point of 7 cm or less. These figures may vary depending on the patient’s age and the target used during testing, but a patient whose results fall within the expected range is generally considered to have adequate convergence for everyday near tasks.
In practice, several factors shift the figures. Older patients tend to show less robust convergence than younger ones, and results obtained with a penlight will often differ from those taken with a printed accommodative target. Neither variation is inherently problematic, but it underlines why the target type must always be noted alongside the measurement; without that context, the numbers are difficult to interpret or compare meaningfully over time.
A break point greater than around 10 cm is commonly used in clinical practice as one indicator of a receded NPC, though cited thresholds vary across the literature depending on the target used, and this should prompt further assessment.
What Does a Receded Near Point of Convergence Mean?
When the break point sits further from the nose than it should, the most likely explanation is convergence insufficiency (CI), a condition in which the eyes cannot sustain the inward effort required for comfortable near vision. It is the defining clinical sign of CI and the starting point for any investigation into the condition.
Patients with convergence insufficiency commonly report the following complaints:
- Headaches and eyestrain that build during reading, writing, or screen use
- Intermittent blurring or doubling of near text, particularly as concentration wanes
- A sense that words are shifting or unstable on the page
- Difficulty maintaining focus on near tasks, or losing their place repeatedly when reading
That said, a receded NPC does not confirm CI on its own. The full picture matters: clinicians will also assess the near phoria, test the positive fusional vergence reserves, and weigh the patient’s reported symptoms before arriving at a diagnosis. The NPC measurement is a critical piece of that picture, but only one piece.
How is Receded NPC Managed?
There is no single protocol for managing a receded NPC. Management depends on symptom severity, patient age, and the wider binocular vision assessment.
Office-based vision therapy, delivered by a clinician and reinforced at home, is the best-supported treatment. A 2020 Cochrane review of CITT trial data found it more effective than pencil push-ups or home computer therapy, which despite being the most commonly prescribed options, performed no better than placebo in trials.
Base-in prism can be incorporated into a spectacle prescription to reduce convergence demand rather than train the system to work harder. Trial evidence found it no more effective than placebo in children, so it’s typically reserved for patients who can’t complete a therapy programme.
Referral becomes appropriate when the NPC is not improving as expected, the binocular vision picture is more complex, or an underlying cause beyond a straightforward convergence issue is suspected.