[Show abstract][Hide abstract] ABSTRACT: Retinoblastoma is typically diagnosed before 5 years of age and is often treated by enucleation (surgical removal) of the cancerous eye. Here, we sought to characterize morphological changes of the cortex following long-term survival from early monocular enucleation.
Nine adults with early right-eye enucleation (≤48 months of age) due to retinoblastoma were compared to 18 binocularly intact controls. Surface area, cortical thickness, and gyrification estimates were obtained from T1 weighted images and group differences were examined.
Early monocular enucleation was associated with increased surface area and/or gyrification in visual (i.e., V1, inferior temporal), auditory (i.e., supramarginal), and multisensory (i.e., superior temporal, inferior parietal, superior parietal) cortices compared with controls. Visual cortex increases were restricted to the right hemisphere contralateral to the remaining eye, consistent with previous subcortical data showing asymmetrical lateral geniculate nucleus volume following early monocular enucleation.
Altered morphological development of visual, auditory, and multisensory regions occurs subsequent to long-time survival from early eye loss.
[Show abstract][Hide abstract] ABSTRACT: The medial geniculate body (MGB) plays a central role in auditory processing with both efferent and afferent tracts to primary auditory cortex. People who have lost one eye early in life have enhanced sound localization, lack visual over auditory dominance and integrate auditory and visual information optimally, similar to controls, despite taking longer to localize unimodal visual stimuli. Compared to controls, people with one eye have decreased lateral geniculate nuclei (LGN) volume as expected given the 50% deafferentation of the visual system. However, LGN volume is larger than predicted contralateral to the remaining eye, indicating altered structural development likely through recruitment of deafferented LGN cells.
Purpose: the current study investigated whether structural MGB changes are also present in this group given the changes they exhibit in auditory processing.
Methods: MGB volumes were measured in adults who had undergone early unilateral eye enucleation and were compared to binocularly intact controls.
Results: unlike controls, people with one eye had a significant asymmetry with a larger left compared to right MGB, independent of eye of enucleation. MGB volume correlated positively with LGN volume in people with one eye.
Conclusions: volume asymmetry in the MGB in people with one eye may represent increased interactions between the left MGB and primary auditory cortex. This interaction could contribute to increased auditory and other left hemisphere-dominant processing, including language, as compensation for the loss of one half of visual inputs early in life. The positive correlation between MGB and LGN volume is not due to space constraints but rather indicates increased plasticity in both auditory and visual sensory systems following early eye enucleation.
[Show abstract][Hide abstract] ABSTRACT: Purpose
Retinoblastoma is a rare eye cancer that generally occurs before 5 years of age and often results in enucleation (surgical removal) of the cancerous eye. In the present study, we sought to determine the consequences of early monocular enucleation on the morphological development of the anterior visual pathway including the optic chiasm and lateral geniculate nucleus.
A group of adults who had one eye enucleated early in life due to retinoblastoma was compared to binocularly intact controls. Although structural changes have previously been reported in late enucleation, we also collected data from one late enucleated participant to compare to our early enucleated participants. Measurements of the optic nerves, optic chiasm, optic tracts and lateral geniculate nuclei were evaluated from T1 weighted and proton density weighted images collected from each participant.
The early monocular enucleation group exhibited overall degeneration of the anterior visual system compared to controls. Surprisingly, however, optic tract diameter and geniculate volume decreases were less severe contralateral to the remaining eye. Consistent with previous research, the late enucleated participant showed no asymmetry and significantly larger volume decreases in both geniculate nuclei compared to controls.
The novel finding of an asymmetry in morphology of the anterior visual system following long-term survival from early monocular enucleation indicates altered postnatal visual development. Possible mechanisms behind this altered development include recruitment of deafferented cells by crossing nasal fibres and/or geniculate cell retention via feedback from primary visual cortex. These data highlight the importance of balanced binocular input during postnatal maturation for typical anterior visual system morphology.
[Show abstract][Hide abstract] ABSTRACT: Stereotypical behaviors in captive polar bears (Ursus maritimus) can be detrimental to their welfare. These behaviors can be reduced through enrichment programs but are often not completely eliminated, so identifying potential triggers is important. The present study investigated the influences of seasonal changes, visitor density, and concurrent bear activity on stereotypical behaviors exhibited by 3 captive polar bears at the Toronto Zoo. All bears exhibited these behaviors; however, individual differences were found in duration and form. The male exhibited less stereotypical behavior during spring, and the females exhibited less stereotypical behavior during winter. An increase in visitor density was associated with more stereotypical behavior in 1 female but less stereotypical behavior in the other 2 bears. All bears engaged in more stereotypical behaviors when the other bears were inactive, and 1 female engaged in more stereotypical behaviors when the other bears were out of sight. Further, when conspecifics were active, all bears engaged in less stereotypical behaviors. Given the variability among individual bears, future enrichment programs must be tailored to the needs of individuals to maximize efficacy.
[Show abstract][Hide abstract] ABSTRACT: Purpose:
It is generally accepted that early visual deprivation from monocular enucleation (ME; the surgical removal of one eye) results in intact spatial vision. Yet, motion perception studies in this population yield inconsistent findings. Here, we investigated speed and luminance contrast perception in a group of ME individuals.
Twelve ME participants (mean age = 24 years; mean age at enucleation = 24 months) and 17 controls (mean age = 25 years) viewing binocularly (BV) and monocularly (MV) completed a series of speed discrimination and luminance contrast detection and discrimination tasks. Stimuli consisted of 0.5 cpd vertical sine wave gratings varying in speed (3.8°/s-24°/s) or luminance contrast (0%-78%). A second set of luminance contrast tasks with 4 cpd gratings teased apart any spatial frequency effects.
The ME group exhibited elevated speed discrimination thresholds compared with BV (P = 0.001) and MV (P = 0.027) controls, but intact luminance contrast discrimination (P = 0.530). Notably, both ME and MV groups displayed elevated luminance contrast detection thresholds compared with the BV group (Ps ≤ 0.006). However, the ME group exhibited slightly lower thresholds compared with MV controls for all 4 cpd tasks.
Our data indicate a disruption in the development of speed perception, but not luminance contrast perception with monocular enucleation. These data highlight the importance of receiving healthy binocular vision during postnatal development for the maturation of cortical regions associated with motion processing.
[Show abstract][Hide abstract] ABSTRACT: PURPOSE.: We investigated the effects of early monocular enucleation (ME) (surgical removal of one eye) on a high-level spatial visual ability, namely face perception. Early monocular deprivation of pattern vision from disorders such as strabismus, amblyopia, or cataract is associated with impairments in low-level spatial vision. This is inconsistent with studies of early ME that show either equivalent or enhanced low-level spatial vision compared with controls. Impairments on some aspects of face perception (i.e., feature-spacing and holistic face processing, both of which mature later in life) have been found with early pattern deprivation from congenital cataract. It is not clear whether the intact low-level spatial vision with ME will also persist with high-level face perception or whether deficits similar to those found with cataract will emerge. METHODS.: We tested individuals who have experienced early ME and controls on a series of high-level spatial visual tasks that measure feature-spacing, feature, and holistic face processing. RESULTS.: The ME group were slower for feature spacing and feature tasks. Furthermore, the ME group did not exhibit the normal pattern of poorer performance on the aligned compared with misaligned composite face discrimination tasks, demonstrating a lack of the composite face effect. However, they did show the normal pattern of poorer performance on same vs. different trials on the aligned tasks. CONCLUSIONS.: These results indicate an impairment in the feature spacing and feature aspects of face perception with ME. They also suggest a present yet, incomplete, development of holistic face processing in this group. Although the complete removal of inhibitory binocular interactions and/or the absence of binocular competition in early ME may result in cortical reorganization of the visual system and preserve low- to mid-level spatial vision, it may be insufficient for the maturation of high-level face perception.
Optometry and vision science: official publication of the American Academy of Optometry 12/2011; 89(2). DOI:10.1097/OPX.0b013e318240488e · 1.60 Impact Factor