Juniper
Publishers- JOJ Ophthalmology
Introduction
Pars plana vitrectomy, peeling of internal limiting
membrane and gas tamponade is currently the standard treatment for
macular hole with high success rate and generally favorable visual
outcomes. Previous studies have indicated that a significant number of
surgically repaired macular hole patients may have persistent outer
retinal defects (microholes) detected with OCT. These are associated
with lower best corrected visual acuity (BCVA) following surgery [1-4].
Previous studies have also reported that such outer retinal defects
represent discontinuities in the ellipsoid zone (EZ) and the external
limiting membrane (ELM) and that there was increased normalization of
the EZ and ELM over the first 12 months of post-op follow-up associated
with improved visual acuity [5-6]. The purpose of this study is to report a series of such cases with long (greater than 1 year) follow up.
Methods
Retrospective case series reviewing medical records
of adults undergoing pars plana vitrectomy (PPV) and gas tamponade for
repair of stage 2 to 4 idiopathic macular holes from 2006 through 2009
at Casey Eye Institute and Devers Eye Institute was performed. Peeling
of internal limiting membrane (ILM) was not performed in any of the
cases. Demographic data, visual acuity, clinical course and optical
coherence tomography (OCT) in post-surgical follow-up visits were
reviewed and recorded. Time domain (TD) Stratus OCT was available and
performed in the early postoperative period followed by spectral domain
(SD) OCT in the later follow up visits. The study was approved by the
institutional review board at Oregon Health and Science University and
was conducted in accordance with the Helsinki Declaration.
Results
During the study period, 80 eyes of 73 patients (25
males and 58 females, mean patient age 67.4 years) with idiopathic
macular holes underwent macular hole surgery with standard pars plana
vitrectomy without Internal limiting membrane peeling, gas tamponade
with either short-acting non-expansile concentrations of sulfur
hexafluoride (SF6) or longer-acting non-expansile perfluoropropane
(C3F8) or hexafluoroethane (C2F6). Macular hole closure was achieved in
61 eyes (76.3%). Post-operative OCT data was available in 43 of these
eyes (70%). Of these 43 eyes, 11 cases (25.5%) presented with persistent
outer retinal defects on OCT at least three months after surgery. The
group consisted of nine females and two males with mean age of 66.8±8.2
years at the time of surgery. Analysis of right versus left eye and
short versus long-acting gas tamponade failed to show any statistically
significant difference among eyes who had persistent outer retinal
defect.
Mean follow up time of these 11 cases was 60.5±43.2
months, with a range of 3 to 118 months. Of these eleven cases, three
had less than one year of follow up due to death (one) or decision not
to follow up further (two), during which time the outer retinal defect
persisted in all three. Another patient had a re-opened macular hole at
approximately a year after surgery but did not undergo further
treatment. Seven eyes had longer follow-up with a minimum of 6 years
(mean 89.8±18.6 months, ranging 72 to 118) (Table 1). Of these eyes, three (42.8%) developed spontaneous late closure of the outer retinal defects (Figure 1).
All three had improved visual acuity after the outer defect was closed
(from average 20/50 to 20/25). The final visual acuity in patients
without a persistent outer retinal defect at the last follow-up was
better than those with a defect, but the difference was not
statistically significant due to small sample size.
Discussion
In our study, the overall rate of macular hole
closure after single primary PPV was similar to previously
contemporaneous reported closure rates using the same technique without
ILM peeling [7-14].
Of note, the routine ILM peel and other advances have increased the
anatomical success rate of MH surgery to more than 90% hole closure.
Successful macular hole closure after surgery is determined clinically
by bio microscopy and a negative Watzke-Allen test and is often verified
with OCT. Several previous studies have evaluated ultra structural OCT
imaging of the foveal region in an attempt to correlate this anatomy
with visual outcomes and have suggested that outer retinal features are
more important than inner retinal features in determining visual acuity [1,2,15-18]. Several studies have reported similar rates of outer retinal defects following successful macular hole surgery [1,2,17,18].
Histopathologic examination of eyes after macular hole surgery has
demonstrated that hole closure start by re-approximation of the edges of
the hole to the retinal pigment epithelium followed by growth of Müller
cells and astrocytes into the hole to fill in the photoreceptor cell
layer [19-24].
This is followed by circumferential and radial contraction of the glial
plug pulling the photoreceptor cell layer toward the center of the
hole. During this process, there is a potential for anterior
displacement of tissue and therefore the presence of a space between
migrating glial and photoreceptor cells from the retinal pigment
epithelium in the central area. This can be viewed in OCT as persistent
outer layer defect and can be seen as focal foveal detachment, ellipsoid
zone disruption or both. Other possible explanations for such defects
include outer retina (Müller cells/ photoreceptor or RPE) damage from
long standing macular hole or surgical trauma during vitrectomy. These
defects can also be associated with decreased visual acuity, although
case reports of outer retinal defects with good visual acuity are
present in the literature [15,19].
Further migration of the glial cell (and/ or photoreceptors) and their
adherence to the retinal pigment epithelium centrally is probably
responsible for healing of such defects and disappearance of the central
OCT defect.
To our knowledge, no other study has investigated the
long term outcome (to the extent of average 60 months post operatively)
of such defects after successful macular hole surgery. A variety of
lesions with similar morphology have been described and referred to as
macular microholes [25].
They are small lamellar defects in the outer retina or retinal pigment
epithelium that occur through a variety of mechanisms, including
spontaneous vitre oretinal interface changes, trauma, photo toxicity,
abortive macular hole formation and other unrecognized causes. The
condition is non progressive, occurs in patients of all ages, and is
compatible with good visual acuity. The retinal changes described in our
study can provide a presumptive patho physiological mechanism and
natural course for such lesions as well. In our study, we observed that a
significant percentage of the outer retinal defects may heal after a
long period of follow up. Although we noticed that such healing can be
associated with improved visual acuity, such observations are very few
in number and also may have been confounded by other factors in the long
follow up interval. Therefore, further studies need to be performed to
determine whether such observed changes in the visual acuity is truly
related to healing of the outer retinal defect. Major limitations of our
study include being retrospective and of relatively small size.
Surgeries were performed by several surgeons and methods. The low
resolution of Stratus images should be recognized as a limitation,
particularly since the premise of the study is to identify subtle outer
retinal defects. Also, 25% of closed macular holes were lost to
follow-up in our center potentially causing significant follow-up bias.
There was a long gap between the early follow up and the late follow up
of many subjects which confounded the interpretation of interval changes
in visual acuity. Similar studies with a larger number of patients and
more frequent and regular follow up evaluation are needed to further
investigate these lesions. And their final outcome.
Conclusion
In this study, a quarter of patients recovering from
macular hole surgery had persistent postoperative outer retinal defects
at one year. About42.8%of these defects improved spontaneously over
time. Visual acuity may improve if the defect closes, although further
studies are needed to investigate such changes.
Financial Disclosure
This research is supported by grant P30 EY010572 from
the National Institutes of Health (Bethesda, MD), and by unrestricted
departmental funding to the Casey Eye Institute from Research to Prevent
Blindness (New York, NY).
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