Download Change in Anterior Chamber Depth Following Vitrectomy

Change in anterior chamber depth following vitrectomy
LI Yang1，YANG Chengxun1, QING Guoping1﹡and WEI Wenbin 1﹡
1. Beijing Tongren Eye Center, Beijing Tongren Hospital, Capital Medical
University; Beijing Ophthalmology & Visual Sciences Key Lab, Beijing, China.
﹡
Correspondence to Wei Wenbin, MD, PhD, No. 1, Dongjiaominxiang, Dongcheng
District, Beijing, 100730, China; Tel: 86-10-5826-9152, Fax: 86-10-5826-9157, E-mail:
[email protected]; or Qing Guoping, MD, PhD; No. 1, Dongjiaominxiang,
Dongcheng District, Beijing, 100730, China; Tel: 86-10-6717-2733,
Fax:
86-10-5826-9930, E-mail: [email protected]
Short running title: ACD change after vitrectomy
Meeting presentation: none.
The authors declare no conflict of interest.
Financial support: the Beijing Municipal Health Bureau High-level Medical
Professionals Promotion Project (No. 2009-3-32 and 2011-3-044)
Word count: abstract 241; text 1720
Keywords: anatomy; anterior chamber depth; vitrectomy; A-scan ultrasound biometry
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Abstract：
Backgound: To characterize the short-term changes of anterior chamber depth (ACD)
in eyes after vitrectomy by means of A-scan ultrasound.
Methods: A prospective case series study was carried out on 29 eyes of 29 patients
who underwent vitrectomy as the sole procedure. ACD was measured using A-scan
ultrasound biometry shortly before vitrectomy and 1 week, 1 month, and 3 months
after the surgery. Post-operative ACDs were compared with baseline.
Results: Twenty-nine patients (16 males and 13 females) were enrolled for the study,
with mean age of 50±11 (25-65) years. Twenty-three eyes of 23 patients were
vitrectomized for vitreous hemorrhage (VH), and the other six were operated for
idiopathic epiretinal membranes (ERM). The mean pre-operative ACD of the VH eyes
was 2.98 ± 0.38mm, No significant difference was found between the ACD of the VH
eyes and their fellow eyes (P=0.058). The average pre-operative ACD in the ERM
eyes was 2.94 ± 0.31mm, which was statistically deeper than that (2.85 ± 0.28) of
their fellow eyes (P=0.008). No statistical difference was found in the post-operative
average ACDs of the VH eyes compared with baseline. In the ERM group, the
post-operative ACD in the surgical eyes were still statistically deeper than the fellow
eyes one week later after surgery (P=0.034). However, such statistical difference
disappeared at the post-operative 1 month and 3 months (P=0.186 and 0.682).
Conclusions: ERM may induce deepening of the ACD, which can be recovered by
uneventful vitrectomy. VH does not cause shift of ACD, neither does vitrectomy.
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Anterior segment morphometry is crucial for ophthalmologists to understand the
visual outcomes of cataract surgery, keratorefractive surgery, as well as some other
anterior segment disorders1-7. Anterior chamber depth (ACD) is one of the most
significant and most widely used parameters among all measurements of the anterior
segment2, 3, 8, 9. However, it is not always consistent. It changes with the position and
thickness of the lens, angle status, and volume of the vitreous body10, 11. Better
understanding of the changes of ACD following surgical treatment is not only
beneficial for predicting visual outcomes of the treatment but also helpful to select
appropriate surgical candidates. For example, gas tamponade in the vitreous cavity
after vitrectomy may lead to shallowing of the anterior chamber and decrease in ACD,
thus the surgeons should be more cautious to use gas tamponade in vitrectomy
candidates with shallow anterior chamber12, 13.
The crystalline lens is one of the most important and frequently measured
structures in the eye ball1, 2, 4, 5, 14-17. It is stabilized centrally in the front globe by lens
zonules at the circumference and hyaloideocapular ligament of Weiger at the posterior
side. The right position and stabilization of the lens is important for good visual
acuity14, 18-20. In vitrectomy, however, the Weiger’s ligament is removed with the
vitreous as part of the procedure. As a consequence, the posterior support of the
crystalline lens vanished after the surgery. Previous reports in literature have shown
that ACD may shift slightly after vitrectomy7, 12, 13, 16, 21. As that fluid-air exchange,
gas or silicone oil tamponade was not excluded in the surgery of these studies, which
may lead to loose of the zonules, it was hard to conclude that the ACD change was a
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result of vitrectomy and removal of the Weiger’s ligament. In this study, we want to
address the over time changes of ACD following uncomplicated vitrectomy as the
sole procedure.
METHODS
A prospective case series of 29 patients (16 males and 13 females) were enrolled for
vitrectomy in our institution from 2011 to 2012. Twenty-three patients were diagnosed
with vitreous hemorrhage (VH). The other six were identified as having epi-retinal
membrane (ERM). Vitrectomy was performed using 23-gauge system shortly after a
detailed ophthalmologic examination including VA, best corrected visual acuity (BCVA),
intraocular pressure (IOP), slit lamp examination, dilated ophthalmoscopy, B-scan
ultrasound, and posterior optic coherence tomography (OCT) if the vitreous body is clear.
ACD was measured by means of A-scan ultrasound shortly before surgery with the
patients in supine position, and was repeated at post-operative one week, one month, and
three months. Each test was repeated 3 times. Accommodation was kept constant by
asking the patient to fixate on a distant target while measuring the ACD.
The inclusion criteria included a best-corrected visual acuity (BCVA) of less than
20/200 due to VH or ERM in the study eye on admission. The fellow eye was free of
ocular diseases or disorders except for mild cataract formation or refractive error (＜
±3.0 spherical equivalent diopters). The exclusion criteria included a history of ocular
trauma, inflammation, intraocular surgery, laser peripheral iridoplasty or iridotomy, a
ciliary cyst or tumor identified by B-scan ultrasound in anyone of the eyes, usage of
nonexpansile gas at the end of the surgery, and age below 18 or above 80 years.
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To avoid inter-personal surgical skill bias, the same doctor (Dr. WWB) performed the
procedures in all included patients. Vitrectomy was performed using a 23-gauge system.
At the completion of the procedure, tobramycin and dexamethasone ointment (Tobradex,
Alcon) were instilled into the conjunctival sac before the eye was patched. Post-operative
care included instillation of tobramycin and dexamethasone eye drops four times daily
from postoperative days 1 to 28.
Statement of Ethics
This study was conducted in Beijing Tongren Eye Center, Beijing Tongren Hospital,
Capital Medical University, Beijing, after the institutional review board and ethics
committee approved the study. All patients provided informed consent after detailed
information about the procedure was performed.
Primary Outcomes
The follow-up examinations included VA, BCVA, IOP, slit lamp biomicroscopy, dilated
ophthalmoscopy, and measurement of ACD by means of B-scan ultrasound in supine
position. Postoperative ACD, VA, BCVA, and IOP were the primary outcome
measurements.
Statistical Analysis
The means of post-operative ACD at post-operative one week, one month, and three
months were compared to baseline with paired sample t-test. The average ACD of the
study eyes was also compared to that of the fellow eyes. The significance level was set at
5%. All statistical analyses were done using Statistical Package for the Social Sciences
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(SPSS) version 16.0 (SPSS, Chicago, IL, USA).
RESULTS
A consecutive case series of 29 (16 males and 13 females) patients were included in
this study due to poor vision secondary to either VH or ERM, which required
vitrectomy to improve visual acuity. The mean age of the patients was 50 ±11 (25-65)
years. Twenty-three patients were diagnosed with VH (13 secondary to proliferative
diabetic retinopathy, 10 with branch retinal vein occlusion). The other six were
identified as having idiopathic macular ERM. All patients underwent uneventful
vitrectomy after admission. Neither silicone oil nor scleral buckle was used at the end
of vitrectomy.
On admission, the average preo-perative ACD in the study eyes and the fellow
eyes were 2.97±0.36 (2.15-3.09) mm and 2.89 ±0.33 (2.13-3.62) mm, respectively. In
the VH eyes, the pre-operative ACD was 2.98 ± 0.38mm, which was not significantly
different from that of their fellow eyes (2.89±0.33 mm, P=0.058). The average
pre-operative ACD in the ERM eyes was 2.94 ± 0.31mm. It was statistically deeper
than that of their fellow eyes (2.85±0.28mm, P=0.008).
During the follow-up visits at one week, 1 month, and 3 months, the average
ACD were 2.97±0.36, 2.96±0.34, and 2.93±0.36mm in the vitrectomized eyes, and
2.90±0.35, 2.93±0.36, and 2.93±0.37mm in the fellow eyes (Table 1). In the ERM
group, the difference in average ACD between the study eyes and fellow eyes existed
one week later after the surgery (P=0.034), but disappeared on post-operative one
month and three months follow-up visits (P=0.186 and 0.682). In VH group, the
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average ACD at post-operative one week, 1 month, and 3 months were 2.97±0.36,
2.92±0.34, and 2.93±0.36mm in the surgical eyes and 2.89±0.36, 2.90±0.38, and
2.91±0.36mm in the fellow eyes. No statistical significance was discerned between
the average ACD between surgical eyes and the fellow eyes at any follow-up visits
(P=0.059, 0.060, and 0.127) (Table 2).
DISCUSSION
In this study we have addressed the changes of ACD following uncomplicated
vitrectomy as the sole procedure in VH and ERM eyes. The results demonstrated that
idiopathic ERM may lead to deepening of the anterior chamber, and this increase of
ACD can be reversed by vitrectomy. VH secondary to either PDR or retinal vein
occlusion does not change the ACD, neither does uneventful vitrectomy.
In previous studies in literature concerning ACD change after intraocular
procedures, the conclusions were generally divided into two categories. One is that
ACD increases obviously after cataract extraction and intraocular lens implantation1, 4,
15, 16, 22
. The other is that ACD fluctuate slightly following surgeries other than cataract
surgery, mostly vitrectomy12, 13, 21, 23. In lens-sparing vitrectomy, the ACD does not
shift obviously though different imaging method was used. One exception is that in
threshold retinopathy of prematurity, the ACD deepened obviously after vitrectomy
and the refraction shifted to more myopic24. In this study, we have measured pre- and
post-operative ACD in 29 patients including 23 VH patients and 6 ERM patients who
underwent uneventful lens-sparing vitrectomy. The post-operative ACDs are not
statistically different with the baseline as a whole group, which indicates that
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successful vitrectomy does not affect ACD and the status of the lens in supine position.
The results were consistent with that of previous reports. However, when splitting the
patients in two groups according to the diagnosis. The condition was different. In VH
group, ACD did not change significantly as compared to that of their fellow eyes. The
post-operative ACDs was neither statistically different from baseline as shown in the
result section. Whereas in ERM group, the average pre-operative ACD was uniformly
greater than that of the fellow eyes, which was statistically significant (p=0.034). This
asymmetry persisted post-operatively until one month later after the surgery (p=0.186
and 0.682 for 1- and 3-month follow-up, respectively). These changes in ACD
indicate that ERM may lead to deepening of the anterior chamber, and such increase
in ACD can be reversed by vitrectomy.
To the best of our knowledge, it has never been reported in literature that ERM
eyes have deeper anterior chamber than their fellow eyes. In this study, however, we
have found that the ACD in ERM eyes was unanimously and statistically deeper than
that of the fellow eyes, which suggested that ERM formation may lead to backward
move of the lens. Although the pathogenesis for idiopathic ERM is still not clear. It is
widely accepted that the degree of visual dysfunction is highly associated with the
thickness and contraction of the membrane. On the one hand, ERM contraction
distorts and detaches the fovea centralis, resulting in marked loss of vision. On the
other hand, the fovea centralis serves as a pivot, allowing ERM contraction to draw
the vitreous backward, which in turn drags the crystalline lens posteriorly through the
Weiger’s ligament. In lens-sparing vitrectomy, the Weiger’s ligament is removed with
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abnormal vitreous. The adhesion on the posterior aspect of the lens disappears and
allows rehabilitation of the anterior chamber after the procedure. This finding may be
of clinical significance in that it revealed that ERM eyes may have a discounted
anterior chamber after lens-sparing vitrectomy. The surgeons should pay more
attention to the angle status of the surgical candidates with pre-operative narrow
angles, especially when gas tamponade is considered at the end of the procedure12.
The limitation of this study is that it is a small sample-size case series study.
Among all enrolled patients, only six patients were identified as having idiopathic
ERM. A large sample-size, well designed, prospective study is necessary before wide
acceptance can be achieved.
In summary, we have found for the first time that idiopathic ERM may lead to
deepening of the anterior chamber, and this increase in ACD can be reversed by
uneventful vitrectomy. VH secondary to either PDR or retinal vein occlusion does not
cause shift of ACD, neither does lens-sparing vitrectomy.
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Table 1. Over time change in ACD following uneventful vitrectomy
VH
ERM
VH ＆ ERM
preoperative
1 week
1 month
3 months
2.98±0.38
2.94±0.31
2.97±0.36
2.97±0.36
2.93±0.30
2.96±0.34
2.92±0.34
2.98±0.44
2.93±0.36
2.93±0.36
2.96±0.41
2.93±0.37
*Values
of the mean anterior chamber depth (ACD)±standard deviation(mm)
†VH=vitreous hemorrhage; ERM=epiretinal membrane
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Table 2 Mean ACD following vitrectomy in both eyes during follow-up visits
preoperative
VH
ERM
VH ＆ ERM
study
2.98±0.38
2.94±0.31
2.97±0.36
1 week
fellow
2.90±0.34
2.85±0.28
2.89±0.33
study
2.97±0.36
2.93±0.30
2.96±0.34
1 month
fellow
2.89±0.36
2.91±0.33
2.90±0.35
*Values
study
2.92±0.34
2.98±0.44
2.93±0.36
3 months
fellow
2.90±0.38
2.99±0.44
2.93±0.36
study
2.93±0.36
2.96±0.41
2.93±0.37
of the mean anterior chamber depth (ACD)±standard deviation(mm)
†VH=vitreous hemorrhage; ERM=epiretinal membrane
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fellow
2.91±0.36
2.96±0.41
2.93±0.37