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Heterophoria is usually asymptomatic. This is when it is said to be "compensated". When fusional reserve is used to compensate for heterophoria, it is known as compensating vergence. In severe cases, when the heterophoria is not overcome by fusional vergence, sign and symptoms appear. This is called decompensated heterophoria.
Method for measuring vertical deviations: 1. The Maddox Rod is held in front of the patient's right eye with the cylinders vertical, making the red line horizontal. 2. The patient is then asked whether the white light is superimposed on the red line or if it appears above or below the red line.
Fixation disparity is a tendency of the eyes to drift in the direction of the heterophoria.While the heterophoria refers to a fusion-free vergence state, the fixation disparity refers to a small misalignment of the visual axes when both eyes are open in an observer with normal fusion and binocular vision. [1]
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. When performing the PFR, prism strengths are increased, placing greater demand on the vergence system, eventually resulting in a break point accompanying diplopia . [ 4 ]
Besides, there is strong evidence of compensation for aberrations between the cornea and intraocular optics in cases of astigmatism (horizontal/vertical) and horizontal coma. The balance of corneal and internal aberrations is a typical example of creating two coupling optical systems.
Patients should be monitored for changes in vision by their eye-care professional. Children of patients should be screened regularly for visual changes related to dominant optic atrophy. Research is underway to further characterize the disease so that therapies may be developed.
The cause of congenital fourth nerve palsy is unclear in most cases. It may be neurogenic in origin, due to a dysgenesis of the CN IV nucleus or nerve, but a clinically similar palsy may result from absence or mechanical dysfunction (e.g., abnormal laxity) of the superior oblique tendon.
Monofixation syndrome (MFS) (also: microtropia or microstrabismus) is an eye condition defined by less-than-perfect binocular vision. [1] It is defined by a small angle deviation with suppression of the deviated eye and the presence of binocular peripheral fusion. [2]