Download Lowry, Kate

Horror Fusionis Following Bilateral Penetrating
Keratoplasties for Keratoconus
Katie Lowry, O.D., B.S.
About the author:
Katie Lowry graduated from the Southern California College of Optometry in May, 2009
and is currently pursuing a residency in Cornea and Contact Lenses from the University of
Houston College of Optometry.
Abstract:
Horror fusionis is a condition describing the inability to fuse simultaneous images and an
absence of suppression. Keratoconus is classically described as a bilateral, non-inflammatory
ectasia resulting in irregular astigmatism and decreased vision. The patient in this case report
underwent bilateral penetrating keratoplasty surgery for the correction of keratoconus, which
resulted in diplopia and horror fusionis.
Key words: horror fusionis, horror fusionalis, keratoconus, intractable diplopia
Case Report
A 22 year old black male presented to the Contact Lens Department of the University
Eye Institute at the University of Houston College of Optometry for a comprehensive vision
evaluation and contact lens fitting. He was referred from an outside practice for the fitting of
rigid contact lenses following bilateral penetrating keratoplasty surgery. He had previously
worn contact lenses prior to the surgeries.
Ocular history was significant for bilateral keratoconus (date of original diagnosis
unknown) and subsequent penetrating keratoplasty in his right eye at age 10 years and in his
left eye at age 11 years, a right esotropia with unknown etiology, and bilateral optic
neuropathy. His medical history was significant for self-reported trauma from a car accident
at the age of 10 months with subsequent hospitalization. He reported having asthma as a
child, and that he was not taking any current medications. He worked in the warehouse of a
major department store.
Presenting visual acuities were 20/30- in the right eye and 20/70 in the left eye. Best
corrected visual acuity with subjective refraction was 20/30 in the right eye and 20/60 in the
left eye. Visual acuity with pinhole showed improvement in the left eye only to 20/50.
Pupils, confrontation visual fields, and near point of convergence were all unremarkable.
Cover test without correction was recorded as an alternating exotropia at distance and near.
The posterior segment was assessed undilated and recorded as unremarkable at this visit.
During the second visit diagnostic gas permeable (GP) contact lenses were fitted and
lenses were ordered. Vision in the right eye remained at 20/30 while vision in the left eye
improved to 20/40 with the diagnostic lenses in place. No diplopia was reported by the
patient at this visit. Despite no improvement in vision in the right eye, GP contact lenses
were ordered for both eyes.
The purpose of the following visit was to dispense the ordered GP lenses and assess
vision, fit and comfort. Uncorrected visual acuities at this visit were 20/30- in the right eye
and 20/80 in the left eye. The contact lenses were placed on his eyes and visual acuity was
found to be 20/30 in the right eye and 20/30 in the left eye. An over-refraction did not
provide any improvement. When viewing binocularly the patient reported constant diplopia
at distance and near. Cover test with the contact lenses in place revealed constant right
esotropia of equal magnitude at distance and near. Upon further questioning the patient
reported that he always saw double, but that the double vision was more disturbing with both
contact lenses in place. The patient reported diplopia with only the right GP in place as well
as with only the left GP in place. The left GP was left in place, as the patient preferred the
left eye, and loose trial lenses were placed over the right eye in an attempt to blur the right
image, but was ineffective. The plan at this visit was to not dispense the contact lenses and
to refer the patient to the Binocular Vision Service for a binocular vision evaluation.
The patient was seen two weeks later for a binocular vision evaluation. During this exam,
the patient again admitted to constant diplopia with and without any visual correction. The
patient was examined without correction at this visit. The assessment was alternating
esotropia measuring 23 prism diopters with horror fusionis. The left eye was the preferred
eye. The diagnosis was made based upon the results of testing in the major amblyoscope
(synoptophore). The patient was unable to fuse simultaneously presented images, and
reported that as the images moved closer together, they would change locations by
“jumping”, thus ending up in opposite positions. The patient was educated on the conditions
and referred back to the Cornea and Contact Lens Service to discuss correction options.
The patient returned to the Cornea and Contact Lens Service the following week to
discuss visual correction options. He reported that although he was diplopic, he preferred to
use his left eye and requested a contact lens for his left eye only. The patient was educated
that he would continue to be diplopic with and without contact lenses. The patient preferred
diplopia with a clear left image as opposed to occlusion of one of the images. The left
contact lens was dispensed for the patient and they were scheduled to return in one week.
A week later he reported that wearing a GP lens in his left eye was a significant
improvement. Although he was still diplopic, he preferred to view the image of his left eye
and ignore the image of his right eye. He subjectively described this as helping to prevent his
eyes from getting tired throughout the day. His only complaint was that he was unable to
wear the contact lens while at work due to the dusty environment of the warehouse. Safety
glasses were prescribed to be worn over the contact lens to prevent irritation from the dust at
his place of work. The patient was referred to the Ocular Diagnostics and Medical Service
for evaluation of bilateral optic neuropathy.
Discussion
Obtaining clear, single, binocular vision normally requires three separate processes:
sensory, integrative and motor.1 The sensory process involves collection and transmission of
visual information to the visual cortex; the integrative process involves synthesis of the two
cortical images allowing a single percept; and the motor process involves the proper
alignment of the two eyes at various distances and directions.1 Horror fusionis occurs
secondary to a deficit in the integrative process, namely there is an inability to fuse the two
cortical images formed by the sensory process.1 Lack of fusion of the two cortical images
results in diplopia, confusion or both.2 Horror fusionis also results in constant, intractable
diplopia because there is an absence of suppression of one of the formed images.3 Horror
fusionis is diagnosed in the major amblyoscope by centering one target on the fovea of the
fixating eye and moving the target of the other eye towards the centered target. The patient
will report that as the peripheral target approaches, it will “jump-over” the central target and
appear on the opposite side.2 Thus showing that no amount of prism will allow fusion of the
two targets.
Common etiologies of intractable diplopia are: a change in the angle of deviation in a
developmental strabismus associated with anomalous retinal correspondence, non-fusible
metamorphopsia, bilateral superior oblique palsy, and sensory fusion disruption syndrome
resulting from a closed head injury.4 Patients who exhibit horror fusionis are more likely to
be congenital esotropes5 and have a history of amblyopia and anti-suppression therapy.6,7
Treatment for horror fusionis includes occlusion by patching, spectacles or contact lenses,
and hypnosis.5 Hypnosis tends to be a last resort and is most useful to help a patient learn to
ignore the second image.5
Keratoconus is a bilateral, but often asymmetric, corneal ectasia classically described as a
non-inflammatory process.8, 9 Ectasia is the dilation or distention of an anatomical structure.
Corneal thinning occurs due to a loss of stromal lamellae, thereby weakening the cornea’s
tensile strength leading to a conical protrusion.10 Keratoconus usually presents in young
adulthood, and vision is affected by corneal changes, including increasing corneal curvature,
Fleischer ring, Vogt’s striae, damage to Descemet’s membrane, and irregular astigmatism.
Spectacles and soft contact lenses are often ineffective forms of treatment for keratoconus
patients due to the inability of these devices to correct for irregular astigmatism Standard
correction involves the use of gas permeable contact lenses, which provide a more regular
refractive surface.10 Keratoconus is a progressive disorder with decreasing visual acuity over
time.11 Eventually, patients may become intolerant to contact lens wear due to unacceptable
fit, vision or comfort and other options may need to be considered. Other treatment options
include intrastromal corneal ring segments (INTACS),12 UV/riboflavin corneal corneal
cross-linking, anterior lamellar keratoplasty, and penetrating keratoplasty.13 Contact lenses
may be fitted (and are often needed) following these surgical treatment options.14
Comment
Horror fusionis can be a disturbing phenomenon for both patients and practitioners.
Patients who have longstanding intractable diplopia may become accustomed to the double
vision and learn to ignore one image, such as in the patient reported in this case report.
Although there is uncertainty as to why the patient developed horror fusionis, an association
with congenital esotropia is suspected. Previous records do not indicate the etiology of the
strabismus, nor do they document any form of vision therapy or anti-suppression therapy.
There was also no indication of diplopia in previous records that were obtained; however
suppression was noted incidentally on one visit. This means that at some point suppression
was present and later it was not. Perhaps the asymmetry and progressed status of
keratoconus at the young age of 10 years allowed for monocular deprivation or significant
aniseikonia and therefore disruption of fusion. After the penetrating keratoplasty surgeries,
the visual acuity was more equalized; however fusion had been already been lost.
This report relates two complex processes that seem to have occurred simultaneously in a
young child, horror fusionis and keratoconus. When rapidly progressing keratoconus
presents in a young child with esotropia, it is imperative to establish and document the
presence or absence of fusion and to monitor development of binocular vision. As
deprivation or aniseikonia occurs with advancing decreased vision from keratoconus,
binocularity should be a major consideration during and after treatment procedures.
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