What are Fusional reserves?
The fusional reserves are the maximum amount the eyes can converge (positive fusional reserves, measured with base out prism) or diverge (negative fusional reserves, measured with base in prism) while still maintaining BSV. As the image doubles, the break point is reached.
Why do we measure Fusional reserves?
Assessing horizontal fusional reserves at near gives you the measure of your patient’s stamina, or ‘petrol in the tank’ to be able to manage their phoria, or ‘posture’.
How is Fusional Reserve measured?
The fusional reserve that opposes the heterophoria is measured first (convergent, using base-out prisms, for exophoria), to blur point (if present), break point, and then the prism is reduced until the recovery of single vision.
What is Fusional vergence Reserve?
Fusional reserves are a measure of how much vergence a person has in reserve that can be used to overcome a heterophoria. It can be useful to watch the patient’s eyes to confirm the break point, that is, when the vergence movement stops.
What is the normal AC A ratio?
The AC/A ratio can indicate the cause of strabismus and help to guide the management. Whether a ratio is considered to be high or low is often based on a so-called normative range that lies between 3-5:1.
How is Fusional convergence measured?
When measuring horizontal fusion ranges, base in prisms assess fusional divergence while base out prisms assess fusional convergence. The vertical fusional vergence amplitude can also be measured with base up and base down prisms although the horizontal PFR is typically the main focus when testing.
How do you measure Vergences?
Vergence ability. To evaluate vergence ability, measure either smooth vergence using Risley prisms in the phoropter or step vergence using prism bars outside of the phoropter.
What is Fusional range?
The prism fusion range (PFR) or fusional vergence amplitude is a clinical eye test performed by orthoptists, optometrists, and ophthalmologists to assess motor fusion, specifically the extent to which a patient can maintain binocular single vision (BSV) in the presence of increasing vergence demands.
What is the normal range of positive fusional vergence and negative Fusional vergence?
Normal Fusional Vergences
| Direction | Fusional Vergence Range (prism dioptres) |
|---|---|
| Vertical | 2-3 |
| Torsional | 2-3 |
| Convergence | 15-20 distance; 25 near |
| Divergence | 6-10 distance; 12 near |
What is normal NPC?
The normal near point of convergence (NPC) is about 6-10 centimeters and the convergence recovery point (CRP) is 15 centimeters. If the NPC is more than 10 centimeters, this is a sign of poor convergence.
What is the normal near point of accommodation?
A normal eye is considered to have a near point at about 11 cm (4.3 in) for a thirty year old. The near point is highly age dependent (see accommodation). A person with hyperopia or presbyopia would have a near point that is farther than normal.