Horror fusionis

Last updated
Horror fusionis
Specialty Ophthalmology

In ophthalmology, horror fusionis is a condition in which the eyes have an unsteady deviation, with the extraocular muscles performing spasm-like movements that continuously shift the eyes away from the position in which they would be directed to the same point in space, giving rise to diplopia. Even when the double vision images are made to nearly overlap using optical means such as prisms, the irregular movements prevent binocular fusion. The name horror fusionis (Latin phrase literally meaning "fear of fusion") arises from the notion that the brain is, or at least appears to be, actively preventing binocular fusion.

Contents

The condition is an extreme type of binocular fusion deficiency. [1]

Symptoms

When the eye position is fully corrected (for example after surgical alignment of the eyes) or when the patient is provided with the best achievable prism correction, the patient does not experience binocular fusion and, instead, sees a double image that is very close to the fixation image and is perceived as "dancing around" it. [2] The eyes display an unsteady misalignment.

Risk factors

Horror fusionis is a rare condition and normally appears only in patients who have been treated by means of surgery or other interventions. [2] Attempts to achieve stereoscopic vision, in particular anti-suppression therapy and other orthoptic exercises, may lead to double vision as undesired side effect, in particular also to horror fusionis.

In terms of outcome of strabismus surgery, monofixation syndrome is considered a better outcome than horror fusionis.

Diagnosis

Horror fusionis is diagnosed using a synoptophore: an image swept across the retina of the nonfixing eye at constant speed is perceived to change its speed in a specific way and then to "jump over" the fixation target. [3]

The specification of horror fusionis is usually distinguished from a more general condition called central fusion disruption syndrome, where the patient is unable to fuse or to suppress. [4]

Management

Bielschowsky's original case was corrected by providing full optical correction to the underlying vision problem.

Generally speaking, if the double vision is intractable by optical and other means and the patient needs relief from the disturbing double images, it may be indicated to use a more modest approach that simply ensures that the image of the weaker eye no longer interferes with the image of the dominant eye. This relieves the most disturbing symptoms, albeit at the cost of offering only subnormal binocular vision.

Diplopia symptoms can be relieved by using spectacles that obscure or blur all or part of the view. This can be achieved for example by applying semi-opaque tape or clear nail polish to a large central portion of one side of a pair of spectacles or to a part of both sides. Alternatively, an opaque contact lens that provides a fogging of the central area may offer better cosmesis. [5] Some patients can achieve peripheral fusion when it is merely a central area that is blended out in this manner. (See also binasal occlusion which obscures the nasal part of the field of view for both eyes.)

A more drastic measure is the insertion of an opaque intraocular lens to obscure the vision of one eye. [6]

History

In 1935, ophthalmologist Alfred Bielschowsky coined the term horror fusionis for this condition. In his case description, the condition was present years after surgical correction of strabismus acquired during childhood and co-existed with aniseikonia. Subsequently, spectacles for size correction ("iseikonic correction") allowed binocular fusion with depth perception to be achieved. Bielschowsky took note that the condition reappeared whenever the spectacles were not worn. [1] [7]

Related Research Articles

Esotropia Form of strabismus

Esotropia is a form of strabismus in which one or both eyes turns inward. The condition can be constantly present, or occur intermittently, and can give the affected individual a "cross-eyed" appearance. It is the opposite of exotropia and usually involves more severe axis deviation than esophoria. Esotropia is sometimes erroneously called "lazy eye", which describes the condition of amblyopia—a reduction in vision of one or both eyes that is not the result of any pathology of the eye and cannot be resolved by the use of corrective lenses. Amblyopia can, however, arise as a result of esotropia occurring in childhood: In order to relieve symptoms of diplopia or double vision, the child's brain will ignore or "suppress" the image from the esotropic eye, which when allowed to continue untreated will lead to the development of amblyopia. Treatment options for esotropia include glasses to correct refractive errors, the use of prisms and/or orthoptic exercises and/or eye muscle surgery. The term is from Greek eso meaning "inward" and trope meaning "a turning".

Binocular vision Ability to perceive a single three-dimensional image of surroundings with two eyes

In biology, binocular vision is a type of vision in which an animal has two eyes capable of facing the same direction to perceive a single three-dimensional image of its surroundings. Neurological researcher Manfred Fahle has stated six specific advantages of having two eyes rather than just one:

  1. It gives a creature a "spare eye" in case one is damaged.
  2. It gives a wider field of view. For example, humans have a maximum horizontal field of view of approximately 190 degrees with two eyes, approximately 120 degrees of which makes up the binocular field of view flanked by two uniocular fields of approximately 40 degrees.
  3. It can give stereopsis in which binocular disparity provided by the two eyes' different positions on the head gives precise depth perception. This also allows a creature to break the camouflage of another creature.
  4. It allows the angles of the eyes' lines of sight, relative to each other (vergence), and those lines relative to a particular object to be determined from the images in the two eyes. These properties are necessary for the third advantage.
  5. It allows a creature to see more of, or all of, an object behind an obstacle. This advantage was pointed out by Leonardo da Vinci, who noted that a vertical column closer to the eyes than an object at which a creature is looking might block some of the object from the left eye but that part of the object might be visible to the right eye.
  6. It gives binocular summation in which the ability to detect faint objects is enhanced.
Far-sightedness Eye condition in which light is focused behind instead of on the retina

Far-sightedness, also known as long-sightedness, hypermetropia, or hyperopia, is a condition of the eye where distant objects are seen clearly but near objects appear blurred. This blurred effect is due to incoming light being focused behind, instead of on, the retina wall due to insufficient accommodation by the lens. Small amount of hypermetropia in young patients is usually corrected by their accommodation, without any defects in vision. But, due to this accommodative effort for distant vision, people may complain asthenopic symptoms while constant reading. Some hypermetropes can see clear at distance, but near vision may be blurred due to insufficient accommodation. For this reason, this defect is referred as far-sightedness. If the hypermetropia is high, there will be defective vision for both distance and near. People may also experience accommodative dysfunction, binocular dysfunction, amblyopia, and strabismus. Newborns are almost invariably hypermetropic, but it gradually decreases as the newborn gets older.

Strabismus Eyes not aligning when looking at something

Strabismus is a condition in which the eyes do not properly align with each other when looking at an object. The eye that is focused on an object can alternate. The condition may be present occasionally or constantly. If present during a large part of childhood, it may result in amblyopia or lazy eyes and loss of depth perception. If onset is during adulthood, it is more likely to result in double vision.

Amblyopia Failure of the brain to process input from one eye

Amblyopia, also called lazy eye, is a disorder of sight in which the brain fails to process inputs from one eye and over time favors the other eye. It results in decreased vision in an eye that otherwise typically appears normal. Amblyopia is the most common cause of decreased vision in a single eye among children and younger adults.

Anisometropia is when two eyes have unequal refractive power. Generally a difference in power of two diopters or more is the accepted threshold to label the condition anisometropia.

Diplopia Double vision

Diplopia is the simultaneous perception of two images of a single object that may be displaced horizontally or vertically in relation to each other. Also called double vision, it is a loss of visual focus under regular conditions, and is often voluntary. However, when occurring involuntarily, it results in impaired function of the extraocular muscles, where both eyes are still functional, but they cannot turn to target the desired object. Problems with these muscles may be due to mechanical problems, disorders of the neuromuscular junction, disorders of the cranial nerves that innervate the muscles, and occasionally disorders involving the supranuclear oculomotor pathways or ingestion of toxins.

Stereopsis is a term that is most often used to refer to the perception of depth and 3-dimensional structure obtained on the basis of visual information deriving from two eyes by individuals with normally developed binocular vision. Because the eyes of humans, and many animals, are located at different lateral positions on the head, binocular vision results in two slightly different images projected to the retinas of the eyes. The differences are mainly in the relative horizontal position of objects in the two images. These positional differences are referred to as horizontal disparities or, more generally, binocular disparities. Disparities are processed in the visual cortex of the brain to yield depth perception. While binocular disparities are naturally present when viewing a real 3-dimensional scene with two eyes, they can also be simulated by artificially presenting two different images separately to each eye using a method called stereoscopy. The perception of depth in such cases is also referred to as "stereoscopic depth".

An eye care professional (ECP) is an individual who provides a service related to the eyes or vision. It is any healthcare worker involved in eye care, from one with a small amount of post-secondary training to practitioners with a doctoral level of education.

Congenital fourth nerve palsy Medical condition

Congenital fourth nerve palsy is a condition present at birth characterized by a vertical misalignment of the eyes due to a weakness or paralysis of the superior oblique muscle.

Worth 4 dot test

The Worth Four Light Test, also known as the Worth's Four Dot test or W4LT, is a clinical test mainly used for assessing a patient's degree of binocular vision and binocular single vision. Binocular vision involves an image being projected by each eye simultaneously into an area in space and being fused into a single image. The Worth Four Light Test is also used in detection of suppression of either the right or left eye. Suppression occurs during binocular vision when the brain does not process the information received from either of the eyes. This is a common adaptation to strabismus, amblyopia and aniseikonia.

Hypertropia Condition of misalignment of the eyes

Hypertropia is a condition of misalignment of the eyes (strabismus), whereby the visual axis of one eye is higher than the fellow fixating eye. Hypotropia is the similar condition, focus being on the eye with the visual axis lower than the fellow fixating eye. Dissociated vertical deviation is a special type of hypertropia leading to slow upward drift of one or rarely both eyes, usually when the patient is inattentive.

Strabismus surgery Surgery to correct strabismus

Strabismus surgery is surgery on the extraocular muscles to correct strabismus, the misalignment of the eyes. Strabismus surgery is a one-day procedure that is usually performed under general anesthesia most commonly by either a neuro- or pediatric ophthalmologist. The patient spends only a few hours in the hospital with minimal preoperative preparation. After surgery, the patient should expect soreness and redness but is generally free to return home.

Polycoria is a pathological condition of the eye characterized by more than one pupillary opening in the iris. It may be congenital or result from a disease affecting the iris. It results in decreased function of iris and pupil, affecting the physical eye and visualization.

Aniseikonia is an ocular condition where there is a significant difference in the perceived size of images. It can occur as an overall difference between the two eyes, or as a difference in a particular meridian. If the ocular image size in both eyes are equal, the condition is known as iseikonia.

Cyclotropia is a form of strabismus in which, compared to the correct positioning of the eyes, there is a torsion of one eye about the eye's visual axis. Consequently, the visual fields of the two eyes appear tilted relative to each other. The corresponding latent condition – a condition in which torsion occurs only in the absence of appropriate visual stimuli – is called cyclophoria.

Stereopsis recovery

Stereopsis recovery, also recovery from stereoblindness, is the phenomenon of a stereoblind person gaining partial or full ability of stereo vision (stereopsis).

Bagolini striated glasses test, or BSGT, is a subjective clinical test to detect the presence or extent of binocular functions and is generally performed by an Optometrist(O.D) or orthoptist or ophthalmologist. It is mainly used in strabismus clinics. Through this test, suppression, microtropia, diplopia and manifest deviations can be noted. However this test should always be used in conjunction with other clinical tests, such as Worth 4 dot test, Cover test, Prism cover test and Maddox rod to come to a diagnosis.

Prism fusion 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. Motor fusion is largely accounted to amplitudes of fusional vergences and relative fusional vergences. Fusional vergence is the maximum vergence movement enabling BSV and the limit is at the point of diplopia. Relative fusional vergence is the maximum vergence movement enabling a patient to see a comfortable clear image and the limit is represented by the first point of blur. These motor fusion functions should fall within average values so that BSV can be comfortably achieved. Excessive stress on the vergence system or inability to converge or diverge adequately can lead to asthenopic symptoms, which generally result from decompensation of latent deviations (heterophoria) or loss of control of ocular misalignments. Motor anomalies can be managed in various ways, however, in order to commence treatment, motor fusion testing such as the PFR is required.

The management of strabismus may include the use of drugs or surgery to correct the strabismus. Agents used include paralytic agents such as botox used on extraocular muscles, topical autonomic nervous system agents to alter the refractive index in the eyes, and agents that act in the central nervous system to correct amblyopia.

References

  1. 1 2 Alfred Bielschowsky (October 1935). "Congenital and acquired deficiencies of fusion". American Journal of Ophthalmology. 18 (10): 925–937. doi:10.1016/s0002-9394(35)92481-3. (abstract)
  2. 1 2 Herbert Kaufmann (January 2004). Strabismus: 72 Tabellen (in German). Georg Thieme Verlag. p. 328. ISBN   978-3-13-129723-5.
  3. ↑ Arthur L. Rosenbaum; Alvina Pauline Santiago (1999). Clinical Strabismus Management: Principles and Surgical Techniques. David Hunter. p. 27. ISBN   978-0-7216-7673-9.
  4. ↑ Arthur L. Rosenbaum; Alvina Pauline Santiago (1999). Clinical Strabismus Management: Principles and Surgical Techniques. David Hunter. p. 28. ISBN   978-0-7216-7673-9.
  5. ↑ D.S. Burger; R. London (1993). "Soft opaque contact lenses in binocular vision problems". Journal of the American Optometric Association (review). 64 (3): 176–180. PMID   8454834.
  6. ↑ Hadid OH, Wride NK, Griffiths PG, Strong NP, Clarke MP (July 2008). "Opaque intraocular lens for intractable diplopia: experience and patients' expectations and satisfaction". The British Journal of Ophthalmology. 92 (7): 912–5. doi:10.1136/bjo.2007.132639. PMID   18556424.
  7. ↑ Brandenburg KC (September 1935). "Aniseikonia". California and Western Medicine. 43 (3): 188–92. PMC   1753774 . PMID   18743367. (full text)
This page is based on this Wikipedia article
Text is available under the CC BY-SA 4.0 license; additional terms may apply.
Images, videos and audio are available under their respective licenses.