Effects of General Anesthesia on Ocular Refraction

PURPOSE

General anesthesia alters the autonomic nervous system. This study aimed to investigate the effects of general anesthesia on objective ocular refraction.

METHODS

A total of 57 patients (112 eyes) under 15 years of age who underwent strabismus surgery under general anesthesia were included in this study. Objective refraction values, corneal refraction values, and pupil diameter were measured using a HandyRef-K, a hand-held refractive keratometer, in the operating room before and during general anesthesia before strabismus surgery.

RESULTS

The spherical power of the myopic eye increased from -0.75 D to -2.29 D (diopter); the cylindrical power increased from -0.90 D to -1.39 D (p < .01 for all). The corneal refractive power decreased by an average of 0.25 D (p < .01). The spherical refractive power was negatively correlated with the age and the amount of change between cycloplegia before general anesthesia and during general anesthesia (r = -0.32, p < .05).

CONCLUSIONS

General anesthesia resulted in manifestation of myopia as noted by the objective refraction values. Corneal refractive values flatten under the same conditions, suggesting that the contraction of the ciliary muscles was the main cause of myopia. We speculate that this change was due to parasympathetic dominance and contraction of the ciliary muscles during general anesthesia.

Characterization of the position of the extraocular muscles and orbit in acquired esotropia both at distance and near using orbital magnetic resonance imaging

PURPOSE

Age-related distance esotropia (ARDE) involves acquired esotropia at distance and phoria at near. However, distance-independent esotropia (DIE) exists esotropia both at distance and near. Thus, we examined the orbital magnetic resonance imaging (MRI) findings for DIE to assess differences in its characteristics.

METHODS

This study was a retrospective case-control study. We evaluated the efficacy of the standard coronal MRI in patients with acquired esotropia and control patients with optic neuritis. Cases with strabismus in the control group were excluded. DIE was defined as having esotropia both at distance and near, and an angle of more than 10 prism diopters at near. The condition of the lateral rectus-superior rectus band, position of rectus muscles, and the volume ratio of the globe to the whole orbit (G/WO) were examined.

RESULTS

The DIE group consisted of 12 eyes of 6 patients (77.3±7.7 years); ARDE group, 38 eyes of 19 patients (73.1±6.8 years); and control group, 34 eyes of 17 patients (70.9±4.3 years). The ratio of abnormality of the lateral rectus-superior rectus bands was higher in the DIE and ARDE groups than in the control group (p<0.01). The vertical angle of the lateral rectus deviated downwards in the control (-7.5±5.1°), ARDE (-12.2±9.1°), and DIE groups (-18.8±5.7°) (p<0.05). The tilting angle of the lateral rectus was tilted temporally in the control (-12.2±9.1°), ARDE (-20.0±8.6°) and DIE groups (-28.6±5.4°) (p<0.01). G/WO was higher in the DIE (0.28±0.01) and ARDE groups (0.27±0.02) compared to the control (0.25±0.03) group (p<0.01).

CONCLUSION

In comparison with the ARDE and control groups, the DIE group presented with abnormalities of the lateral rectus-superior rectus band, malposition of the lateral rectus, and differences in the G/WO. The DIE group showed a more severe form of ARDE.

Clinical Features of Crowded Orbital Syndrome on Magnetic Resonance Imaging

We have previously reported strabismus due to mismatch of orbital volume and globe as 'crowded orbital syndrome' (COS). In this study we have used magnetic resonance imaging (MRI) to investigate its clinical features. This has revealed that a globe with a similar axis occupies a larger volume in the orbit in patients with COS than in controls without strabismus. This suggests that strabismus with high myopia may easily occur in those with relatively small orbits and axial elongation. In acquired esotropia and/or vertical strabismus, a mismatch of orbital volume and globe axis should be investigated with MRI.

Standard coronal orbital magnetic resonance imaging is an effective technique for diagnosing sagging eye syndrome

PURPOSE

The aim of this study was to determine the importance and efficacy of the standard coronal magnetic resonance imaging (MRI) analysis method for the correct clinical diagnosis of the sagging eye syndrome.

METHODS

This retrospective study evaluated the standard coronal MRI efficacy by comparing the positions of the orbital pulleys and extraocular muscles in patients with sagging eye syndrome as well as controls. The participants included 50 patients with sagging eye syndrome (aged 73.3 ± 6.7 years) and 17 age-matched control patients (aged 70.9 ± 4.3 years) that presented optic neuritis. The participants were classified into groups of age-related distance esotropia and cyclo-vertical strabismus. Lateral rectus-superior rectus band condition, lateral rectus vertical angle, lateral rectus tilting angle, and superior rectus-lateral rectus displacement angle were examined.

RESULTS

The lateral rectus-superior rectus band was more frequently disordered in the two groups than that in the control. The lateral rectus vertical and tilt angle examinations exhibited a significant difference in the age-related distance esotropia [(- 13.3 ± 10.9°, p < 0.05) and (- 24.1 ± 9.5°, p < 0.01)] and cyclo-vertical strabismus [(- 11.9 ± 6.9°, p < 0.05) and (- 20.8 ± 9.3°, p < 0.01)] groups compared with those in the control group [(- 7.5 ± 5.1°) and (- 12.2 ± 9.1°)]. The superior rectus-lateral rectus displacement angle did not present a significant difference between the patients and control groups.

CONCLUSIONS

Patients with sagging eye syndrome exhibited disordered orbital pulley and extraocular muscle malposition, as determined by standard coronal magnetic resonance imaging, indicating the effectiveness of the procedure for diagnosing sagging eye syndrome.

Pre- and postsynaptic effects of brimonidine on isolated rabbit iris dilator muscles

Purpose

Brimonidine is an imidazoline compound used for the treatment of glaucoma, but having very little effect on pupil diameter. Like para-aminoclonidine, most imidazoline compounds interact with postsynaptic α-adrenoceptors and cause pupil dilatation. Therefore, as part of an investigation of the mechanism of action of brimonidine on pupil diameter, the present study was initiated to measure, in vitro, the relative potency of brimonidine on the pre- and postsynaptic α-adrenoceptors of rabbit iris dilator muscle.

Methods

The contractile activity of brimonidine and its effect on twitch contraction evoked by electrical field stimulation were studied in isolated rabbit iris dilator muscles by isometric tension recording.

Results

Brimonidine significantly inhibited the twitch contraction of the dilator muscle caused by field stimulation, without affecting the response to exogenously applied phenylephrine. Compared to phenylephrine, brimonidine caused only a small contractile response with % maximum contraction values of <10%.

Conclusion

These results suggest that brimonidine may act on nerve endings to inhibit adrenergic neurotransmission with very little effect on postsynaptic α-adrenoceptors. This may indicate that brimonidine reduced the pupil diameter just a little, thus improving night vision.

Short-term evaluation of Trabectome surgery performed on Japanese patients with open-angle glaucoma

PURPOSE

To evaluate the short-term results of Trabectome surgery performed on Japanese patients.

METHODS

Retrospective observational study. Trabectome surgery was performed on 117 eyes from 101 patients at Kitasato University Hospital from December 2010 to June 2013, involving 48 eyes with primary open-angle glaucoma (POAG), 62 eyes with secondary open-angle glaucoma (SOAG), and 7 eyes with developmental glaucoma. Trabectome surgery alone was performed on 34 phakic eyes (the phakic group) and 35 pseudophakic eyes (the pseudophakic group), and Trabectome surgery combined with phacoemulsification (the combined surgery group) was performed on 48 eyes. The main outcomes assessed were intraocular pressure (IOP), number of IOP-lowering medications, and success probabilities using Kaplan-Meier life-table analyses. Failure risk factors were identified using the Cox proportional hazards ratio.

RESULTS

In all cases, after a mean follow-up of 18.5 ± 13.5 months, IOP was reduced from 31.6 ± 9.9 (SD) mmHg using 5.0 ± 1.7 medications to 16.4 ± 5.4 mmHg using 3.8 ± 1.8 medications. One year after surgery, IOP was reduced from 29.4 ± 7.8 to 16.1 ± 3.8 mmHg in POAG, from 33.6 ± 11.1 to 14.7 ± 2.9 mmHg in SOAG, from 33.0 ± 10.2 to 15.7 ± 3.3 mmHg in the phakic group, from 32.6 ± 9.3 to 15.3 ± 3.0 mmHg in the pseudophakic group, and from 29.9 ± 10.0 to 15.2 ± 3.0 mmHg in the combined surgery group. There were no statistically significant differences in IOP at each measurement point, either between POAG and SOAG or among the three procedure subtypes. The POAG and SOAG success rates at 12 months using postoperative IOP ≤ 21 mmHg and ≥20 % reduction in baseline as criteria were 53.9 and 77.2 %, respectively (p = 0.024, log-rank test). Twenty-one eyes (17.9 %) needed additional trabeculectomy. None of the univariate and multivariate risk factors for failure were detected.

CONCLUSIONS

Trabectome surgery is safe and effective for Japanese patients whose target IOP is 18 mmHg or above. However, it is necessary to carefully consider Trabectome surgery for advanced POAG cases.