Primary angle-closure glaucoma (PACG) is a subtype of
glaucoma that affects 16 million people worldwide, of whom
4 million are bilaterally blind. This prevalence of PACG
is expected to increase to 21 million cases by 2020, and it
is expected that 5.3 million people will become bilaterally
blind by the disease. The majority of those affected by
PACG are Asians, which currently account for 87% of all
cases (1).
PACG is characterized by optic nerve damage, increased
intraocular pressure (IOP) or peripheral anterior synechia,
and iridotrabecular contact of at least 180o
viewed through
gonioscopy (2,3). It differs from primary angle closure
(PAC) in that the PACG case presents with evidence of
increased IOP or peripheral anterior synechia, but without
glaucomatous optic neuropathy (3).
Initial therapy for PACG consists of performing laser
peripheral iridotomy (LPI), which creates a channel
through the peripheral iris in order to relieve the pupillary
block component (2), however a significant number of
patients also require further medical therapy and/or surgery
to control their elevated IOP (4).
During recent years, numerous studies have investigated
lens extraction surgery as a treatment for PACG (5-11).
For example, phacoemulsiffcation surgery in patients with
PACG has repeatedly led to a significant and sustained
reduction in IOP, thereby controlling PACG progression.
Notably, Barbosa et al. showed that clear lens extraction
was more effective than topical medications in controlling
IOP after LPI surgery in ffve consecutive cases of PACG.
In particular, the investigators reported four of the five
patients achieving IOP <22 mmHg without requiring any
topical medications after phacoemulsiffcation (5). Similarly,
Lam et al. (7) studied a cohort of 62 patients with PACG
of Chinese ethnicity and showed phacoemulsification
to be superior to LPI in lowering IOP 18 months after
an acute PAC episode. They also showed that patients
who had been treated with phacoemulsification required
signiffcantly less medications (mean: 0.03±0.18) to control
their IOP 18 months post-operatively compared to the LPI
group (mean: 0.90±1.14). Tham et al. further showed that
phacoemulsification and trabeculectomy were comparable
at reducing IOP in medically uncontrolled PACG patients,
with trabeculectomy causing more adverse events compared
to phacoemulsiffcation (8).
Although the exact mechanism by which lens extraction
surgery lowers IOP is not fully understood, hypotheses
include: (I) anterior chamber (AC) deepening and increased
trabecular outflow due to lens removal with backward
rotation of the ciliary body, relieving compression on the
trabecular meshwork and canal of Schlemm; (II) postoperative
release of prostaglandin F-2 contributing to
increased uveoscleral outflow; (III) post-operative fibrosis
and contraction of the posterior lens capsule causing
traction on the ciliary body, resulting in hyposecretion of aqueous humor; (IV) an increased AC volume resulting
from removing a 5-mm thick crystalline lens and replacing
it by a 1-mm thick artiffcial lens increases the volume of AC
required to be filled by aqueous humor (11).
Although many studies, including the above, reported
the role of lens extraction in PACG, they have been met
with skepticism. While LPI is first line standard of care,
a very safe and tested procedure with minimal adverse
effects, lens extraction is an invasive surgery with potential,
but rare, post-operative complications such as retinal
detachment, endophthalmitis, and cystoid macular edema.
Furthermore, intraocular lens (IOL) insertion leads to
decreased accommodation, which might be uncomfortable,
especially for younger patients. In addition to these
concerns, systematic literature reviews conducted by
independent researchers have questioned the efficacy of
clear lens extraction in PACG. In a 2006 Cochrane database
systematic review, Friedman and Vedula concluded that
there was little evidence from high quality randomized
trials or non-randomized studies to support lens extraction
as treatment of chronic PACG (12). Another comprehensive
literature review by Tarongoy similarly expressed uncertainty
at the role of lensectomy for treating PACG (13).
The recent results of the effectiveness of early lens
extraction for the treatment of PAC glaucoma (EAGLE)
study, offer fresh, systematic and much more convincing
evidence of the use of lens extraction in PACG patients (3).
Consisting of 419 participants with early stage disease from
30 hospitals in five countries (Australia, mainland China,
Hong Kong, Malaysia, United Kingdom), the EAGLE
study followed patients for 36 months and performed a
head to head comparison of clear lens extraction with LPI
to determine comparative efficacy for each treatment (3).
Assessing IOP, quality of life (QoL) scores and incremental
cost effectiveness ratios, the study showed increased efffcacy
and decreased serious adverse events amongst patients
who received lens extraction surgery compared to LPI.
The study concluded that patients receiving clear lens
extraction had a 0.052 higher mean health status score
on the European Quality of Life-5 Dimensions (EQ-5D)
questionnaire (95% CI, 0.015–0.088, P=0.005) compared to
patients treated with LPI. Furthermore, mean IOP was also
1.18 mmHg lower (95% CI, −1.99 to −0.38, P=0.004) in
the clear lens extraction group compared to the LPI group.
The study also measured the economic consequences of
performing lens extraction surgery: 179 of the patients
recruited in the United Kingdom had their associated costs
of performing LPI or lens extraction recorded. Amongst
study participants, lens extraction cost £981 (95% CI,
£612–£1,317) more on average compared to LPI. However,
patients treated with lens extraction also had a mean Quality
Adjusted Life Year (QALY) gain of 0.069 (95% CI, −0.017
to 0.159), demonstrating measurable beneffts in patients’
life quality with the increased treatment cost. No patients
in either group had any serious adverse events, however
irreversible loss of vision occurred in only one patient
who received clear lens extraction compared to three
patients who received standard of care.
Though far from conclusive, this study offers the most
signiffcant evidence to date of the effectiveness of clear lens
extraction as an effective treatment for PACG.Through
its large sample size and international multi-center study
design, the EAGLE study offers the largest and most diverse
patient cohort out of any study examining the therapeutic
role of phacoemulsification in PACG. Not only does this
study demonstrate significant therapeutic advantages, but
also addresses adverse effects issues, showing clear lens
extraction to be a relatively safe alternative to the current
standard of care.
It is important to note however, that this study
excluded patients younger than 50 years to avoid patients
losing accommodation post-operatively. As a result, the
study’s QoL score did not take into account the potential
discomfort that would be experienced by younger patients
who were treated with phacoemulsification. Secondly,
the study also excluded certain patient groups, limiting
its generalizability. Specifically, patients with advanced
glaucoma or concurrent cataracts, as well as those who
had PAC with IOP less than 30 mmHg were excluded.
Thirdly, all clear lens extraction surgeries in this study
were performed by highly experienced surgeons, which
may explain the low complication rates. Fourthly, visual
ffeld outcomes for both LPI and lens extraction groups did
not differ significantly after 36 months, therefore, longer
follow-up may be needed to show potential functional
differences between the groups. Finally, the mean age of
enrolled patients in this study was 67, at which age most
patients develop some degree of cataracts. Hence, the term
“clear lens extraction” should be used with caution when
studying this patient segment.
In conclusion, the EAGLE study has validated the role of
clear lens extraction in treating PACG, showing convincing
evidence of the therapeutic benefits over LPI. However,
further studies are needed before lens extraction can replace LPI as the gold standard in treating PACG.
