Faden procedure

A strabismus surgery where the belly of a rectus muscle is sutured to the sclera posterior to the globe’s equator. This fixates the muscle in a posteriorly displaced position, reducing its ability to rotate the eye when contracting without altering the resting eye alignment. The Faden procedure selectively weakens a muscle’s pulling force while preserving its resting tone. It is often used for the medial rectus muscles in convergence excess esotropia.

first-degree fusion

The ability to superimpose or fuse dissimilar targets or images seen by the two eyes into a single, unified percept. It involves cortical processing of binocular visual input to combine the different views from each eye into one coherent 3D image. First-degree fusion is a fundamental aspect of binocular vision and stereopsis, allowing depth perception. Disruptions can lead to diplopia or suppression, and it is tested by presenting different targets to each eye.

fixating eye

In strabismus or eye misalignment, the fixating eye refers to the non-deviating eye that is fixating on the target and has normal alignment. It is the eye being used for fixation, while the non-fixating eye is the deviating eye that is turned inwards, outwards, upwards, or downwards.

fixation disparity

Fixation disparity is a subtle misalignment of the eyes that occurs during binocular viewing, where each eye slightly deviates from perfect alignment while still maintaining single vision. It can cause symptoms such as eyestrain and headaches, particularly during tasks that require sustained visual attention.

forced duction test

A procedure performed under local or general anesthesia to assess mechanical restrictions of eye movements. It involves grasping the conjunctiva with forceps and attempting to rotate the eye in the direction of the restricted movement. A positive forced duction test, where rotation is limited, indicates a tight muscle or other mechanical restriction causing the strabismus. In contrast, a negative test suggests paralysis of the extraocular muscle.

Fresnel press-on prisms

A Fresnel lens is a compact lens made from a series of concentric grooves that allows the lens to capture more oblique light from a large area while maintaining a thin, flat profile. Fresnel press-on prisms are low cost, temporary means of providing prismatic correction.

full-muscle transposition

A surgical procedure used to treat complete extraocular muscle palsies like third or sixth nerve palsies where the entire tendon of a rectus muscle is disinserted from its original scleral insertion. The disinserted rectus muscle is then transposed and sutured adjacent to the insertion of the paretic rectus muscle. This augments the function of the paralyzed muscle by adding vector forces from the transposed muscle.

functional amblyopia

fusional convergence

The inward movement of the eyes to maintain binocular single vision when fusion is disrupted, without a change in accommodation. It occurs in response to disparity cues and is driven by the fusional vergence system to realign the visual axes onto the object of regard. Fusional convergence helps compensate for phoric deviations and maintain comfortable binocular vision at a given viewing distance.