Korean J Ophthalmol.  2019 Oct;33(5):436-445. 10.3341/kjo.2019.0036.

Effects of Orbital Decompression on Lamina Cribrosa Depth in Patients with Graves' Orbitopathy

• Seo Y
• Shin WB
• Bae HW
• Yoon JS

• KMID: 2459525
• DOI: http://doi.org/10.3341/kjo.2019.0036

Abstract

PURPOSE
We sought to investigate the effects of Graves' orbitopathy (GO) and orbital decompression on lamina cribrosa depth (LCD) using spectral-domain optical coherence tomography.
METHODS
Forty eyes that underwent orbital decompression to relieve compressive optic neuropathy or correct disfiguring exophthalmos in the context of GO were included. Subjects were imaged with spectral-domain optical coherence tomography before surgery and at 1 and 3 months after surgery, at which the examiner measured the LCD (distance from the anterior surface of the lamina cribrosa to the Bruch membrane opening line) and peripapillary retinal nerve fiber layer thickness. Subjects were divided into two groups"”a muscle-dominant group composed of patients who had extraocular muscle enlargement on preoperative orbital computed tomography scan and a fat-dominant group composed of patients who did not show extraocular muscle enlargement on preoperative orbital computed tomography scan"”and subgroup analysis was performed. Preoperative and postoperative intraocular pressure, exophthalmos, LCD, and retinal nerve fiber layer thickness were evaluated.
RESULTS
At baseline, LCD was remarkably shallower in the muscle-dominant group than in the fat-dominant group (95% confidence interval, p = 0.007). In the muscle-dominant group, LCD showed no definite change after surgery. However, the fat-dominant group showed temporary posterior displacement of the lamina cribrosa at 1-month postoperation that was reversed to baseline at 3 months postoperation (95% confidence interval, p < 0.01).
CONCLUSIONS
The lamina cribrosa was anteriorly displaced preoperatively, and its position was nearly unchanged after the surgery, especially in association with extraocular muscle enlargement. An enlarged extraocular muscle could reduce the pressure-relieving effect of orbital decompression around the scleral canal in patients with GO.

Keyword

Decompression; Extraocular muscles; Graves ophthalmopathy; Optic nerve; Optical Coherence tomogrphy

MeSH Terms

Bruch Membrane
Decompression*
Exophthalmos
Graves Ophthalmopathy
Humans
Intraocular Pressure
Nerve Fibers
Optic Nerve
Optic Nerve Diseases
Orbit*
Retinaldehyde
Tomography, Optical Coherence
Retinaldehyde

Figure

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  Fig. 1 Microstructural changes of orbital anatomy after orbital decompression surgery. (A) Change in mean magnitude of lamina cribrosa depth (LCD), prelaminar tissue thickness, and Bruch membrane opening (BMO) at each follow-up visit (preoperation and 1 and 3 months postoperation) (analyzed by repeated-measures ANOVA with Bonferroni method for multiple comparison, *p < 0.05). (B) Comparison of LCD change between the muscle-dominant group and fat-dominant group. In the muscle-dominant group, the position of the lamina cribrosa showed no definite change in the postoperative periods compared with at baseline. In the fat-dominant group, the position of the lamina cribrosa was posteriorly displaced at 1 month postoperation and reversed at 3 months postoperation. (C) Representative images for comparison of LCD change between the muscle-dominant group and fat-dominant group. B-scan images were obtained preoperatively and at 1 and 3 months postoperatively from patients who underwent orbital decompression. A reference line was set by connecting the termination of Bruch's membrane (yellow solid line). Green solid line: B-scan-acquired site in optic nerve head.

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  Fig. 2 Lamina cribrosa (LC) depth change in subjects diagnosed with compressive optic neuropathy due to Graves' orbitopathy before orbital decompression.

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  Fig. 3 Schematic illustration of the change in lamina cribrosa depth after orbital decompression, comparing the fat-dominant group and the muscle-dominant group. (A) In the fat-dominant group, at baseline, retrobulbar pressure (RBP) was lower than that of the muscle-dominant group. Therefore, the translaminar pressure difference moves to the posterior surface of the lamina cribrosa. After orbital decompression, the RBP decreased, and the net translaminar pressure difference increased toward the same direction. (B) In the muscle-dominant group, at baseline, the RBP was relatively larger than that of the fat-dominant group, and the translaminar pressure difference was directed toward the anterior surface of the lamina cribrosa. After surgery, intraocular pressure (IOP) and RBP decreased slightly at the same time. Therefore, there was no definite change in translaminar pressure difference. Cerebrospinal fluid pressure is not indicated in this diagram under the assumption that it did not change after the surgery.

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  Fig. 4 Change of intraorbital structure in patients of two groups (A, fat-dominant group; B, muscle-dominant group) between the preoperative and postoperative periods on orbital computed tomography scans. (A) In the fat-dominant group, extraocular muscle and optic nerve seemed to lose their tension temporarily at 1 month after surgery but was restored at 3 months after surgery. (B) In contrast, in the muscle-dominant group, there was only a slight change in tension of the extraocular muscle and optic nerve compared to the fat-dominant group.

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