Changes as the result of ageing in extraocular muscles: a post-mortem study

Revisiting the surgical table: An analysis of surgical dose-response in Asian exotropia

BACKGROUND

Previous research on the factors associated with surgical dose-response in strabismus surgery for exotropia has yielded inconsistent results. This study determined the factors influencing surgical dose-response in exotropia patients who underwent recession and resection (R&R).

METHODS

Exotropia patients who underwent unilateral R&R at the National Taiwan University Hospital between 2006 and 2021 were evaluated. Deviation-angle differences in prism diopters (PD) were measured preoperatively and at 1 month postoperatively. Surgical dose-response (PD/mm) was defined as the difference in deviation angle (in PD) divided by the surgical dose in millimeters. Linear and non-linear regression models were used to evaluate the influence of variables including age, sex, axial length, and preoperative deviation on surgical dose-response.

RESULTS

Overall, 295 patients (162 children; 133 adults) were included. Average surgical dose-response in the pediatric and adult groups was 2.82 ± 0.60 PD/mm and 3.02 ± 0.62 PD/mm, respectively. Male sex was negatively correlated with surgical dose-response in children. The surgical dose-response was larger in adults with longer axial length (>25.64 mm) and patients with larger preoperative deviation (>42.6 PD and >38.7 PD in pediatric and adult groups, respectively). Surgical dose-responses peaked at 35.1 years.

CONCLUSION

Age, axial length, and preoperative deviation have a nonlinear effect on surgical dose-responses in exotropia patients undergoing R&R. Surgical dose-responses were larger in patients in young adulthood, with longer axial length and larger preoperative deviation angle. A table with fitted values for surgical dose-response based on age, axial length, and preoperative deviation was established for clinical reference.

The Immunoarchitecture of Human Extraocular Muscles

Purpose

The purpose of this study was to describe the immunoarchitecture of normal extraocular muscles (EOMs) in terms of presence, distribution, and organization of various immune cells.

Methods

We performed unilateral orbital exenterations in six fresh human cadavers from elderly patients, followed by dissection of the medial, lateral, superior and inferior rectus, superior and inferior oblique, and superior palpebral levator muscle in their entirety. We further cross sectioned each EOM in an anterior, central, and posterior third. After immunohistochemical staining for CD3, CD8, CD20, CD138, CD68, and podoplanin, quantitative analysis was performed.

Results

We found all EOMs (rectus, oblique, and levator muscles) to harbor both T- and B-lymphocytes, with a B-lymphocyte dominance and an absence of plasma cells. The highest prevalence of immune cells was seen in the muscle bellies, with, on average, 488 ± 63 CD3+ T-lymphocytes and 44 ± 110 CD20+ B-lymphocytes per mm2, and significant differences from the anterior (T-lymphocytes) and posterior (T- and B-lymphocytes) thirds. T- and B-lymphocytes were primarily organized in hotspots in the vicinity of blood vessels. In addition, a small resident population of macrophages scattered throughout the specimens was detected. No lymphatic vessels were found in any of the EOMs.

Conclusions

These findings can serve as a reference dataset in the assessment of EOM biopsies in the diagnostic process of inflammatory orbital and systemic disorders. Moreover, from a regenerative perspective, our results highlight the importance of taking into account the presence of a resident immune cell population when studying the host immune response on transplanted tissues or engineered constructs.

Comparison of subjective cyclofusion ranges and objective ocular torsion in normal participants according to age

PURPOSE

To investigate the relationship between subjective cyclofusion ranges and objective ocular torsion in normal participants according to age.

METHODS

This cross-sectional study included 120 participants aged ≥ 20 years with no ocular diseases. The subjective cyclofusion ranges were measured centrifugally and centripetally in the direction of excyclotorsion and incyclotorsion, respectively, concurrently with rotational diplopia production by rotation using synoptophore. Disc fovea angle (DFA) was defined as the angle formed by two lines: a line passing through the center of the optic nerve papilla and fovea and a horizontal line passing through the center of gravity of the optic papilla using fundus photographs.

RESULTS

The participants were aged 49.1 ± 17.7 years. The total cyclofusion centrifugal (sum of extorsion and intorsion) and centripetal ranges were 10.9 ± 2.2° and 7.2 ± 1.8°, respectively, both of which decreased in participants in their 60 s and 70 s (p < 0.01). The DFA was - 7.0 ± 3.4° in the right eye (- : excyclo, + : incyclo) and - 8.0 ± 3.2° in the left, which was associated with age (p < 0.001). The correlation between the DFA and centrifugal (r =  - 0.13, p = 0.16) and centripetal (r =  - 0.002, p = 0.99) cyclofusion ranges of extorsion was not significantly different. The centrifugal (r = 0.37, p < 0.001) and centripetal (r = 0.40, p < 0.001) cyclofusion ranges of intorsion were positively correlated.

CONCLUSION

Subjective cyclofusion ranges decreased in both extorsion and intorsion in the elderly. Objective ocular torsion showed excyclotorsion with age. When strabismus surgery is performed in elderly patients with torsional strabismus, the decrease in subjective cyclofusion ranges should be considered.

Motor learning by selection in visual working memory

Motor adaptation maintains movement accuracy over the lifetime. Saccadic eye movements have been used successfully to study the mechanisms and neural basis of adaptation. Using behaviorally irrelevant targets, it has been shown that saccade adaptation is driven by errors only in a brief temporal interval after movement completion. However, under natural conditions, eye movements are used to extract information from behaviorally relevant objects and to guide actions manipulating these objects. In this case, the action outcome often becomes apparent only long after movement completion, outside the supposed temporal window of error evaluation. Here, we show that saccade adaptation can be driven by error signals long after the movement when using behaviorally relevant targets. Adaptation occurred when a task-relevant target appeared two seconds after the saccade, or when a retro-cue indicated which of two targets, stored in visual working memory, was task-relevant. Our results emphasize the important role of visual working memory for optimal movement control.

Natural Course of Mild Graves Orbitopathy: Increase of Orbital Fat But Decrease of Muscle Volume With Increased Muscle Fatty Degeneration During a 4-Year Follow-Up

PURPOSE

To describe the natural course of orbital fat volume and extraocular muscle volume in mild Graves orbitopathy during a 4-year follow-up. To describe fatty changes within the extraocular muscles.

PATIENTS

Twenty-five patients with mild Graves orbitopathy, who did not require any therapeutic intervention other than supportive therapy, were followed for 4 years.

METHODS

CT scans were performed in all patients at baseline and follow-up. A validated technique using Mimics (Materialise) was used to calculate fat and muscle volumes. Outcomes were compared with previously collected data. The amount of intramuscular fat was assessed on CT scans in a semi-quantitative way by two blinded observers according to a four-point scale.

RESULTS

After a median follow-up of 4.3 years, the median fat to orbital volume ratio increased with 0.08 from 0.57 to 0.65 (p = 0.000), whereas the median muscle volume to orbital volume ratio decreased with 0.03 from 0.17 to 0.14 (p = 0.000). In this control group in patients between 49 and 54 years old, the changes were 0.01 and -0.002, respectively. The Clinical Activity Score decreased to zero (p = 0.000), and the median eyelid aperture decreased from 12 to 10 mm (p = 0.007). A significant increase of intramuscular fat was found in patients with Graves orbitopathy.

CONCLUSIONS

The natural course of mild Graves orbitopathy, as observed over 4 years, is characterized by an increase of orbital fat volume, a decrease in muscle volume, and an increased intramuscular fatty degeneration.

Effect of Visual Search Training on Saccades in Age-related Macular Degeneration Subjects

OBJECTIVE

To compare the impact of unilateral versus bilateral Age-related Macular Degeneration (AMD) on saccadic movements, and to show the effect of visual search training on these eye movement performances in AMD subjects. We hypothesized that unilateral and bilateral AMD subjects had abnormal saccadic performances, and that visual search training could improve their performances.

METHODS

Three groups participated in visual search training: 13 elderly unilateral AMD subjects (mean age: 74.6 ± 1.6 years), 15 elderly bilateral AMD subjects (mean age: 74.2 ± 1.2 years), and 15 healthy age-matched control subjects (mean age: 70.9 ± 1.3 years). Horizontal saccadic performances were recorded before and after visual search training (Metrisquare®) with the Mobile Eye Tracker (Mobile EBT®). We analyzed the saccadic movement performances: latency, mean velocity and gain. We measured the training performances for each exercise: the time, the number of omissions and the number of errors. We analyzed the performances with Kruskal-Wallis and posthoc tests.

RESULTS

The latency of saccades in AMD subjects is significantly longer compared to healthy elderly for 15° (p<0.03), 10° (p<0.003) and 5° (p<10-3). Unilateral and bilateral AMD subjects normalized their latency of saccades after training for small saccades (respectively p=0.30 and p=0.23 for 10°, and p=0.09 and p=0.52 for 5°). In elderly, performances depend on the saccade's amplitude.

CONCLUSION

AMD subjects' saccadic movements are disrupted: the execution needs more time but is efficient. The visual search training improved the saccadic performances in AMD subjects. Further studies will aim to improve knowledge on such issues and to explore the benefit of training over time in unilateral AMD subjects.

Ultrastructural changes of extraocular muscles in strabismus patients

Strabismus is an ocular disorder characterized by partial or complete inability to keep eye alignment. It represents a very common ocular problem at ophthalmology clinics worldwide. The current study aimed to show the most encountered ultrastructural changes in extraocular muscles (EOMs) collected from patients with different forms of strabismus. Nine specimens of EOMs were collected from five patients during strabismus correction surgery and processed for light and electron microscopy examinations. Histologically, skeletal muscle fibers in normal EOMs appeared tight and normally arranged with clear striations. In strabismic muscles, the fibers appeared disarranged, and atrophied, swollen and disintegrated in some situations. By transmission electron microscopy, normal EOMs were formed of skeletal muscle fibers with intact basal membrane and sarcolemma, tightly aligned myofibrils with well-arranged sarcomeres, Z line and H zone, and normally distributed mitochondria. On the other hand, strabismic EOMs revealed vacuolation and degeneration of myofibrils, accumulation of lipid droplets, subsarcolemmal inclusions and clustering of mitochondria. EOMs obtained from a Down syndrome patient with V-pattern infantile esotropia showed extensive vacuolation and disintegration of myofibrils, and extra- and intracellular deposition of collagen fibers. Interestingly, some skeletal muscle cells exhibited features of autophagic cell death with a trial of engulfing process by neighboring cells. In conclusion, our study traces some characteristic ultrastructural changes in strabismic EOMs, most notably, extensive vacuolation, clustering of mitochondria, degeneration of myofibrils and autophagic changes. These changes might be emphasized as possibly secondary to strabismus.

Histopathological changes of fibrosis in human extra-ocular muscle caused by botulinum toxin A

We report the histopathological findings in 3 patients where injections of botulinum toxin were used prior to strabismus surgery. In all cases we found evidence of permanent extraocular muscle atrophy and fibrosis.

Effects of aging on eye movements in the real world

The effects of aging on eye movements are well studied in the laboratory. Increased saccade latencies or decreased smooth-pursuit gain are well established findings. The question remains whether these findings are influenced by the rather untypical environment of a laboratory; that is, whether or not they transfer to the real world. We measured 34 healthy participants between the age of 25 and 85 during two everyday tasks in the real world: (I) walking down a hallway with free gaze, (II) visual tracking of an earth-fixed object while walking straight-ahead. Eye movements were recorded with a mobile light-weight eye tracker, the EyeSeeCam (ESC). We find that age significantly influences saccade parameters. With increasing age, saccade frequency, amplitude, peak velocity, and mean velocity are reduced and the velocity/amplitude distribution as well as the velocity profile become less skewed. In contrast to laboratory results on smooth pursuit, we did not find a significant effect of age on tracking eye-movements in the real world. Taken together, age-related eye-movement changes as measured in the laboratory only partly resemble those in the real world. It is well-conceivable that in the real world additional sensory cues, such as head-movement or vestibular signals, may partially compensate for age-related effects, which, according to this view, would be specific to early motion processing. In any case, our results highlight the importance of validity for natural situations when studying the impact of aging on real-life performance.

Saccade adaptation as a model of flexible and general motor learning

The rapid point-to-point movements of the eyes called saccades are the most commonly made movement by humans, yet differ from nearly every other type of motor output in that they are completed too quickly to be adjusted during their execution by visual feedback. Saccadic accuracy remains quite high over a lifetime despite inevitable changes to the physical structures controlling the eyes, indicating that the oculomotor system actively monitors and adjusts motor commands to achieve consistent behavioral production. Indeed, it seems that beyond the ability to compensate for slow, age-related bodily changes, saccades can be modified following traumatic injury or pathology that affects their production, or in response to more short-term systematic alterations to post-saccadic visual feedback in a laboratory setting. These forms of plasticity rely on the visual detection of accuracy errors by a unified set of mechanisms that support the process known as saccade adaptation. Saccade adaptation has been mostly studied as a phenomenon in its own right, outside of motor learning in general. Here, we highlight the commonalities between eye and arm movement adaptation by reviewing the literature across these fields wherever there are compelling overlapping theories or data. Recent exciting findings are challenging previous interpretations of the underlying mechanisms of saccade adaptation with the incorporation of concepts including prediction, reinforcement and contextual learning. We review the emerging ideas and evidence with particular emphasis on the important contributions made by Josh Wallman in this sphere over the past 15 years.

Molecular and cellular adaptations to chronic myotendinous strain injury in mdx mice expressing a truncated dystrophin

Myotendinous strain injury is the most common injury of human skeletal muscles because the majority of muscle forces are transmitted through this region. Although the immediate response to strain injury is well characterized, the chronic response to myotendinous strain injury is less clear. Here we examined the molecular and cellular adaptations to chronic myotendinous strain injury in mdx mice expressing a microdystrophin transgene (microdystrophin(DeltaR4-R23)). We found that muscles with myotendinous strain injury had an increased expression of utrophin and alpha7-integrin together with the dramatic restructuring of peripheral myofibrils into concentric rings. The sarcolemma of the microdystrophin(DeltaR4-R23)/mdx gastrocnemius muscles was highly protected from experimental lengthening contractions, better than wild-type muscles. We also found a positive correlation between myotendinous strain injury and ringed fibers in the HSA(LR) (human skeletal actin, long repeat) mouse model of myotonic dystrophy. We suggest that changes in protein expression and the formation of rings are adaptations to myotendinous strain injury that help to prevent muscle necrosis and retain the function of necessary muscles during injury, ageing and disease.

Early onset of lipofuscin accumulation in dystrophin-deficient skeletal muscles of DMD patients and mdx mice

Lipofuscin, the so-called ageing pigment, is formed by the oxidative degradation of cellular macromolecules by oxygen-derived free radicals and redox-active metal ions. Usually it accumulates in post-mitotic, long-lived cells such as neurons and cardiac muscle cells. In contrast, it is rarely seen in either normal or diseased skeletal muscle fibres. In this paper, we report that lipofuscin accumulates at an early age in both human and murine dystrophic muscles. Autofluorescent lipofuscin granules were localized, using confocal laser scanning microscopy and electron microscopy, in dystrophin-deficient skeletal muscles of X chromosome-linked young Duchenne muscular dystrophy (DMD) patients and of mdx mice at various ages after birth. Age-matched normal controls were studied similarly. Autofluorescent lipofuscin granules were observed in dystrophic biceps brachii muscles of 2-7-year-old DMD patients where degeneration and regeneration of myofibres are active, but they were rarely seen in age-matched normal controls. In normal mice, lipofuscin first appears in diaphragm muscles nearly 20 weeks after birth but in mdx muscles it occurs much earlier, 4 weeks after birth, when the primary degeneration of dystrophin-deficient myofibres is at a peak. Lipofuscin accumulation increases with age in both mdx and normal controls and is always higher in dystrophic muscles than in age-matched normal controls. At the electron microscopical level, it was confirmed that the localisation of autofluorescent granules observed by light microscopy in dystrophin-deficient skeletal muscles coincided with lipofuscin granules in myofibres and myosatellite cells, and in macrophages accumulating around myofibres and in interstitial connective tissue. Our results agree with previous biochemical and histochemical data implying increased oxidative damages in DMD and mdx muscles. They indicate that dystrophin-deficient myofibres are either more susceptible to oxidative stress, or are subjected to higher intra- or extracellular oxidative stress than normal controls, or both.

Age-related changes and the possible adaptability of rat jaw muscle spindles: immunohistochemical and fine structural studies

Afferent signals from jaw muscle spindles contribute to the feedback mechanism that regulates mastication. The integrity and adaptability of this proprioceptor to age-related changes of the surrounding structures are therefore essential to maintain an appropriate masticatory function throughout life. In this study, we examined muscle spindles obtained from temporal and masseter muscles of 10-week-, 12-, 18-, and 24-month-old Wistar rats, employing immunohistochemistry for protein gene product 9.5 (PGP 9.5) or growth-associated protein (GAP-43) in addition to transmission electron microscopy, in order to investigate their morphological changes in relation to the effect of aging on the adaptive potential of the receptors. Immunohistochemistry for PGP 9.5 showed virtually similar reactions at sensory nerve terminals in all age groups. On the other hand, immunoreactivity for GAP-43 in the sensory nerve ending of the muscle spindles was found 2 and 3 weeks after birth but became almost undetectable by 10 weeks. However GAP-43 immunoreactions occasionally reappeared in those of spindles in 12- and 18-month old animals, and vanished again by 24 months of age. Electron microscopic observations also revealed age-related morphological changes in the intrafusal muscle fibers of the rats in 12-month and older groups. The extent of degenerative and/or atrophic alterations of intrafusal fibers increased with age and involved the nerve elements of spindles by 24 months. These findings indicate that the adaptation potential of rat jaw muscle spindles is well preserved until middle age, but diminishes in elderly animals. Structural changes of muscle spindles in elderly animals probably contribute to the deterioration of the muscular function.