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The Four Prism Dioptre Reflex Test (also known as the 4 PRT, or 4 Prism Dioptre Base-out Test) is an objective, non-dissociative test used to prove the alignment of both eyes (i.e. the presence of binocular single vision) by assessing motor fusion.
- BD: base down prisms - BU: base up prisms - BO: base out prisms - BI: base in prisms - eso: esotropia - exo: exotropias - L/R: left hypertropia or right hypotropia - R/L: right hypertropia or left hypotropia Double Maddox rod test. The double Maddox rod test can also be used to assess torsion and measure cyclotropias.
The Krimsky test is essentially the Hirschberg test, but with prisms employed to quantitate deviation of ocular misalignment by determining how much prism is required to centre the reflex [2] The Krimsky test is advisably used for patients with tropias, but not with phorias.
For example, Base in (BI), Base out (BO), Base up (BU) or Base down (BD). The angle of the deviation with the units in prism dioptres. Which eye is fixating and which eye is deviating. Whether the test was performed with or without an abnormal head posture.
If the residual esotropia is small, or if the patient is unfit or unwilling to have surgery, prisms can be incorporated into their glasses to provide more permanent symptom relief. When the deviation is too large for prismatic correction to be effective, permanent occlusion may be the only option for those unfit or unwilling to have surgery.
Suppression of an eye is a subconscious adaptation by a person's brain to eliminate the symptoms of disorders of binocular vision such as strabismus, convergence insufficiency and aniseikonia. The brain can eliminate double vision by ignoring all or part of the image of one of the eyes. The area of a person's visual field that is suppressed is ...
Treatment options for esotropia include glasses to correct refractive errors (see accommodative esotropia below), the use of prisms, orthoptic exercises, or eye muscle surgery. The term is from Greek eso meaning "inward" and trope meaning "a turning".
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.
Dissociated vertical deviation (DVD) is an eye condition which occurs in association with a squint, typically infantile esotropia. The exact cause is unknown, although it is logical to assume it is from faulty innervation of eye muscles.
Prism correction is measured in prism dioptres. A prescription that specifies prism correction will also specify the "base". The base is the thickest part of the lens and is opposite from the apex. Light will be bent towards the base and the image will be shifted towards the apex.