International Ophthalmology 24: 25–26, 2002.
© 2002 Kluwer Academic Publishers. Printed in the Netherlands.
25
Change in lens thickness after trabeculectomy
Raphael Rasooly, Larry Benjamin & Robert Casson
The Ophthalmology Department, Stoke Mandeville Hospital, Aylesbury, UK
Received 19 November 1999; accepted 3 June 2001
Cataract is a common late complication of trabeculectomy [1–4], but the cause remains unclear. Relatively
little data exist concerning the nature of lens changes
in the early period after trabeculectomy [5–10]. One
measurable parameter which indicates a disruption to
lens homeostasis is a change to its thickness [11].
We performed a pilot study using ultrasonography to
measure the change in lens thickness after trabeculectomy by measuring the lens thickness in six patients
with primary open angle glaucoma before and after
trabeculectomy. We obtained informed consent from
all participants in accordance with the Declaration
of Helsinki. The patients’ ages ranged from 42 to
91 years and all patients had been instilling timolol
0.25% twice daily pre-operatively. We used an Allergan A-scan ultrasound to measure the lens thickness
immediately pre-operatively and at successive postoperative visits. Cyclopentolate 1% was instilled to
obtain cycloplegia in each patient prior to the measurements. All patients had uncomplicated surgery and
no eyes were hypotonous post-operatively. Patients
instilled cyclopentolate 1%, chloramphenicol 0.5%,
and dexamethasone 0.1% into the operated eye for
two weeks. The first post-operative measurements
were taken within three days of surgery and measurements continued for up to seven months until the
lens thickness stabilized or returned to its preoperative
level.
The Allergan A-scan ultrasound has an error of
±0.035 mm and the accuracy was refined by averaging many readings. We measured the intraocular
pressure (IOP) with a Goldman applanation tonometer
just prior to each set of ultrasound measurements. The
average change in lens thickness in the early postoperative period is shown in Figure 1. These findings
suggest a significant disruption to lens homeostasis
as a consequence of uncomplicated trabeculectomy.
Whilst the change in lens thickness was reversible in
four patients, in two patients it persisted. We pro-
pose the alteration in lens morphology may be a
manifestation of a cataractogenic insult.
The incidence of cataract following trabeculectomy based on retrospective data has been variably
reported as between 5–37% [1–4], and is dependent
on the length of follow up. Cataract after trabeculectomy has been linked with age, a flat anterior chamber,
myopia, an IOP greater than 30 mmHg and hypotony [5–10]. An increased incidence of cataract has
been found when the trabecular meshwork is excised
from anterior to posterior [13]. Interestingly the incidence of cataract progression after deep sclerectomy
has been reported to be only 7% percent [14].
Nemeth and Horoczi measured changes in axial
length, anterior chamber depth, lens thickness, vitreous length, and scleral thickness in 10 eyes four days
after trabeculectomy [5]. They found a decreased anterior chamber depth, and thickened sclera but did not
find a significant change in lens thickness. However,
since only one post-operative measurement was taken
it is possible that a significant change in lens thickness
went unnoticed.
The cause of the change in lens thickness after uncomplicated trabeculectomy remains speculative. The
changes in lens thickness that were demonstrated in
our study probably represent an increase in the water
content of the lens resulting in swelling. The lens is
kept in a state of relative dehydration by active transport mechanisms, which counteract the tendency of
water to enter the lens cells. The permeability properties of the lens cells also determine the electrolyte
balance [15]. The combination of the active transport
system and the permeability profile of the lens cells
has been termed the “pump leak system” [16].
The most important active transport mechanism
is the Na+/K+ pump located in the anterior epithelium. Dysfunction of the pump causes loss of osmotic
homeostasis and an increase in lens hydration. In addition a disruption of the normal cell permeability prop-
26
References
Figure 1. Average change in lens thickness after trabeculectomy.
erties may cause a loss of osmotic balance [15]. The
earliest lens opacities after trabeculectomy with antimetabolite have been reported to occur in the anterior
subcapsular region [10]. We speculate that trabeculectomy directly affects the pump-leak system, perhaps
by altering aqueous dynamics. In most eyes this represents a reversible injury, but in eyes with marginal
lens epithelial function this may be a cataractogenic
insult. An alternative explanation for the change in
lens thickness is a possible relationship with the IOP.
The limitations of our findings clearly relate to the
small number of subjects and the use of ultrasound
to measure small changes in lens thickness. Although
only six eyes were studied a consistent change in lens
thickness was demonstrated, which was considerably
greater than the potential error of the measurements.
In conclusion, we have demonstrated a change in
lens thickness after trabeculectomy and suggest that
this represents a potentially cataractogenic insult. We
propose a similar study involving a larger number of
subjects using Scheimpflug photography to more accurately measure lens changes after trabeculectomy.
Given the reported low incidence of cataract after deep
sclerectomy a comparison study examining morphologic lens changes after deep sclerectomy would be
useful.
1. D’Ermo F, Bonomi L, Doro D. Critical analysis of long term
results of trabeculectomy. Am J Ophthalmol 1979; 88: 829–
35.
2. Mills KB. Trabeculectomy: a retrospective long-term followup of 444 cases. Br J Ophthalmol 1981; 65: 790–5.
3. Ridgway AEA. Trabeculectomy-a follow-up study. Br J Ophthalmol 1974; 58: 680–6.
4. Tornqvist G, Drolsum LK. Trabeculectomies. A long-term
study. Acta Ophthalmologica (Copenh) 1991; 69(4): 450–4.
5. Nemeth J, Horoczi Z. Changes in the ocular dimensions after
trabeculectomy. International Ophthalmol 1992; 16: 355–357.
6. Bonomi L, Marchini G, de Franco I, Perfetti S. Prospective
study of the lens changes after trabeculectomy. Dev Ophthalmol (Basel) 1989; 17: 97–100.
7. Pillai S, Mahmood MA, Limaye SR. Transient lenticular opacification following trabeculectomy. Ophthalmic Surg 1988;
19(7): 508–9.
8. Clarke MP, Vernon SA, Sheldrik JH. The development of
cataract following trabeculectomy. Eye 1990; 4(pt 4): 577–83.
9. Vesti E. Development of cataract after trabeculectomy. Acta
Ophthalmologica (Copenh) 1993; 71(6): 777–81.
10. Daugeliene L Yamamoto T, Sawada A, Kitazawa Y. An image
analysis study of cataract development after trabeculectomy
with mitomycin C. Ophthalmologica 1998; 212(4): 244–9.
11. Kinoshita JH. Pathways of glucose metabolism in the lens.
Invest Ophthalmol 1965; 4: 619.
12. Watson Pg. Trabeculectomy. A modified Ab Externo Technique. Ann Ophthalmol 1970; 2: 199–205.
13. Watson PG, Grierson I. The place of trabeculectomy in the
treatment of glaucoma. Ophthalmology 1981; 88: 175–96.
14. Karlen ME, Sanchez E, Schnyder CC, Sickenberg M, Mermoud A. Dee sclerectomy with collagen implant: medium
term results. Br J Ophthalmol 1999 Jan; 83(1): 6–11.
15. Hart WM. Adler’s Physiology of the Eye. 9th ed. St. Louis:
Mosby-Year Book Inc., 1992.
16. Kinsey VE, Reddy DVN. Studies on the crystalline lens, XI,
The relative role of the epithelium and capsule in transport.
Invest. Ophthalmol 1965; 4: 104.
Address for correspondence: L. Benjamin, The Ophthalmology Department, Stoke Mandeville Hospital, Aylesbury HP21 8AL, UK
Phone: (01296) 315034; Fax: (01296) 315037
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