Meter angle (MA) The amount of convergence required for each eye to fixate an object located at a distance from the eyes in the median plane
"Convergence insufficiency (CI) is a common binocular vision disorder that is often associated with a variety of symptoms, including eyestrain, headaches, blurred vision, diplopia [double vision], sleepiness, difficulty concentrating, movement of print while reading, and loss of comprehension after short periods of reading or performing close activities."
therefore, it is of considerable clinical significance aggravated by lack of sleep, reduction of general well-being, and anxiety.
Characteristically one eye will be closed or closed while reading to obtain relief from visual fatigue
Pupil dilatation may be observed at this stage, which is an additional indicator of convergence failure
2.0 convergence insufficiency b
Disjugate simultaneous and synchronous inward
rotation of both eye which results from co-
contraction of the two medial rectus muscles
Allows bifoveal single vision maintained at near
Does not deteriorate with age
Can be improved by exercises
Unit of measurement
Clinical measurement – Prism Diopter
The amount of convergence is calculated by using
the formula: 1/d × IPD where
d is the distance and IPD is interpupillary distance.
Thus, a 6-cm IPD requires 6 dioptres of
convergence for a fixation distance of 1 m.
due to the tone of the extraocular muscles
initiating movement from the anatomical position
which is initiated by the stimulus of
which is initiated by a fusional stimulus.
an involuntary vergence movement to maintain
induced by the awareness of a near object
One-third of convergence relates to tonic, fusional
and proximal convergence.
Two-thirds is accommodative
NPC value is greater than 10 cm
Inability of eyes to obtain or maintain adequate
Most common cause of ocular asthenopic
First described by von Graefe in 1855 and later
elaborated by Duane
one of the most common causes of ocular
most common cause of muscular asthenopia
Clinical signs of CI
1) Exophoria greater at near than at distance(N>D)
2) A receded near point of convergence
3) Reduced positive fusional vergence at near
4) Low AC/A ratio
5) Little or no lag of accommodation
Symptoms due to muscular fatigue
Eye strain and sensation of tension around globe.
Headache and eye ache after intense near work and
relieved when eyes are closed
Difficulty in changing focus from distance to near
Itching, burning and soreness of eyes and even
hyperemia of nasal half of the conjunctiva
Symptoms due to failure to
Blurred vision and crowding of words while reading
Intermittent crossed diplopia for near under the
condition of fatigue
If untreated, in some cases, convergence insufficiency can
lead to an outward eye turn that comes and goes
Less common complaints
gritty sensation in the eyes
Aetiology of CI
Primary or idiopathic:
In many cases, exact etiology is not known.
May be associate with:
Delayed or inadequate functional development
Over work or worry
Associated with uncorrected high hyperopia
High hyperopes (>5D) usually make no effort to
accommodate and there is deficient
Myopes may not need accommodation and
thus lack accommodative convergence.
Vertical muscle imbalances
Consecutive convergence insufficiency :
May occur following either recession of medial
recti or resection of lateral rectus
General physical causes
diseases of endocrine gland (e.g. Mobius’ sign in thyroid
include anxiety and neurosis
Clinical problem in patient who does intense near
Children with increased school work.
Discomfort usually occurs at the end of the day.
Assessment of NPC
The near point of convergence is assessed
objectively using either a fixation target or the
fixation target on the RAF rule
Assessment of PFV
Base out motor fusion range is measured to find out
blur, break and recovery
Prism Cover test
Assess Latent ocular deviation such as exophoria at
distance and near
Near exophoria greater than distance exophoria
Near exophoria distance orthophoria
Diagnosis of CI
Type I: NPC receded or Decreased PFV
Type II: NPC receded or PFV decreased and XP N> XP
Type III: All the clinical signs present
Proper refractive correction for any presence of
Myopes given full correction and hyperopes
under corrected to stimulate accommodation
Base in prism
Plus reading glasses
Aperture rule trainer
Pencil push ups
Increase amplitude of
BI/BO prism flipper
Training of voluntary convergence
Base –in prism reading glasses or bifocals with
prism in the lower segment are useful as
Relieving prisms and bifocals should be
prescribed cautiously in young age
As a last resort, when all other measures fail.
When it is associated with large exophoria at near.
Medial muscle resection can be performed in one
or both eyes.