tonometer prism sterilisation
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Tonometer prism sterilisation: A local and UK national survey
Aman Chandra a, Allon Barsam b, Christopher J. Hammond a,*
a West Kent Eye Centre, Princess Royal University Hospital, Farnborough, Kent BR6 8ND, UKb Department of Ophthalmology, Queen Mary’s Hospital, Sidcup, Kent DA14 6LT, UK
bstract
urpose: First to audit local adherence to a protocol of use of an alcohol wipe for each tonometry, and secondly to assess current practice
ationally in the UK.
ethod: The audit was carried out at two units: The West Kent Eye Centre at the Princess Royal University Hospital (Orpington, UK) and
ueen Mary’s Hospital (Sidcup, UK). The standard set for this audit was 100% sterilisation. During a 1-week period in November 2005, the
umber of alcohol wipes was counted in each consultation room after outpatient clinics, with the doctors being assessed blind to the survey.
he number of Goldman applanation tonometry intra-ocular pressures recorded by each clinician was counted by inspection of the medical
ecords of patients seen.
Secondly, departments listed in the UK Directory of Training Posts were contacted by telephone and the senior nurse was interviewed.
hey were asked directly about their department’s tonometer prism sterilisation and management.
esults: The local audit showed only 54% of tonometry measurements were associated with sterilisation using an alcohol-impregnated wipe.
he national survey included 140 of the 152 UK training departments. Thirty-three (23.6%) departments used disposable tonometer prisms
outinely. The remaining 107 (76.4%) used non-disposable prisms. Eighty-five (60.7%) departments provided sodium hypochlorite for prism
terilisation, with 69 (81.2%) of these departments providing more than one prism/clinician to allow full exposure to the disinfectant. Twenty-
wo (15.7%) departments used alcohol wipes. Only 8 (7.5%) of the 107 departments using non-disposable prisms tracked these prisms, despite
oyal College of Ophthalmologists guidelines that they should be. These same 8 (7.5%) departments replaced the non-disposable prisms as
er manufacturer guidelines. 19.3% of charge nurses were aware of a policy for tonometry in patients with, or at risk of, prion disease.
onclusions: This study highlights that sterilisation of tonometer prisms was inconsistent in a local audit. Nationally, practices were varied.
he majority of ophthalmology departments continued to use non-disposable tonometer prisms, but few seemed aware of the Royal College of
phthalmologists’ recommendation that disposable prisms are used in patients at risk of prion disease, and few track tonometer heads or
eplace them according to manufacturers guidelines. Use of disposable tonometer prisms would seem to reduce concerns about sterilisation, as
ell as prevent spread of common pathogens.
2007 British Contact Lens Association. Published by Elsevier Ltd. All rights reserved.
www.elsevier.com/locate/clae
Contact Lens & Anterior Eye 31 (2008) 13–16
eywords: Tonometer; Prisms; Sterilisation; Audit; Survey
1. Introduction
Tonometer prisms are an integral part of ophthalmic
examination. They are known to be a potential vector in
iatrogenic transmission of pathogens [1]. Prion disease such
as Creutzfeld–Jacobs Disease (CJD) is of particular concern,
and applanation tonometer prisms have been suggested as a
possible source of infection [2]. As the United Kingdom
may be an area of relatively high risk, the Royal College
* Corresponding author. Tel.: +44 1689 865682; fax: +44 1689 863329.
E-mail address: chammond@btopenworld.com (C.J. Hammond).
367-0484/$ – see front matter # 2007 British Contact Lens Association. Publi
oi:10.1016/j.clae.2007.07.004
of Ophthalmologists (RCOphth) guidance advises use of
disposable tonometers for patients either diagnosed, at
risk of, or suspected of prion disease, but fall short of
recommending disposable tonometer prisms for all patients.
It is suggested that non-disposable prisms should be wiped
and disinfected between use, and should not be moved
between individual clinical stations so any outbreaks may be
tracked easily [3]. Manufacturers recommend that their
tonometer prisms be replaced after 100 uses, though the
extent of adherence to this guidance is not known.
The aim of this study was twofold. The first aim was to
audit the rate of sterilisation of non-disposable tonometer
shed by Elsevier Ltd. All rights reserved.
A. Chandra et al. / Contact Lens & Anterior Eye 31 (2008) 13–1614
prisms in two District General Hospital (DGH) ophthalmol-
ogy departments. The second aim was a national survey of
UK ophthalmology departments to assess current sterilisa-
tion practice, to identify policies regarding tonometer
prisms, and in particular whether there were local policies
in place for patients with possible CJD.
2. Method
The two DGH departments included in the audit
recommend wiping the tonometer head after each Goldmann
applanation tonometry (GAT) with a single 70% isopropyl
alcohol-impregnated swab, followed by wiping the prism
with a dry tissue. The West Kent Eye Centre at the Princess
Royal University Hospital (Orpington, UK) has around
25,000 ophthalmology outpatient attendances per annum,
and Queen Mary’s Hospital (Sidcup, UK) sees similar
numbers of patients. The standard set for this audit was
100% tonometer prism sterilisation. During a 1-week period
in November 2005, the number of alcohol wipes was
counted in each consultation room after outpatient clinics,
with the doctors being assessed blind to the survey (to avoid
change of practice during the audit). The number of GAT
intra-ocular pressures recorded by each clinician was
counted by inspection of the medical records of patients
seen during the session. Results of individual doctors
were anonymised, but the grade of clinician was recorded. It
was assumed that alcohol wipes were only used for the
purpose of cleaning tonometer prisms. Doctors involved in
the clinics were asked about this after the week of data
collection, and none could recall any other occasion they had
used these.
For the second part of the survey, departments listed in
the UK Directory of Training Posts were contacted by
telephone and an interview with the senior nurse manager in
charge of the clinic was arranged at a time convenient to
him/her. Four direct questions were asked:
� W
hat is your department’s method of tonometer prismsterilisation?
� I
f you use non-disposable tonometer prisms, did you trackthem?
� D
o you replace your tonometer prisms as per manufac-turer guidelines?
� A
re you aware of a local protocol for tonometry forpatients with, or at risk of, CJD?
Fig. 1. Local audit results showing the proportion of Goldmann applanation
tonometry measurements when a 70% isopropyl alcohol-impregnated swab
was used.
3. Results
3.1. Local audit
The total number of patients who had had their intra-
ocular pressures (IOP) measured was 203. The total number
of alcohol wipes used was 110 (54% of IOPs). Therefore, the
number of patients who had their IOPs measured without
the use of alcohol wipes was at least 93 (46%) (Fig. 1).
This differed between different grades of doctors. The
non-consultant grade doctors measured 165 patient’s GAT
intra-ocular pressures and used 79 alcohol wipes (47.9%).
Consultants measured 38 patients’ GAT intra-ocular
pressures and used 27 alcohol wipes (71.1%).
3.2. National survey
For the survey, interviews were conducted with the senior
nurse in 140 (92%) of the 152 ophthalmology departments
listed in the Directory of Training Posts.
With regard to their methods of sterilisation, 107 (76.4%)
departments used non-disposable tonometer prisms routi-
nely. Sodium hypochlorite was used in 85 (60.7%) depart-
ments and 69 (81.2%) of these departments provided more
than one prism/clinician to allow full exposure to the
disinfectant. Alcohol wipes were used in 22 (15.7%)
departments. Non-disposable prisms were tracked by eight
departments (7.5%). These same 8 (7.5%) departments
replaced their prisms as per guidelines. Disposable tono-
meter prisms were used in the remaining 33 (23.6%)
departments (Fig. 2). Twenty-seven (19.3%) of the surveyed
were aware of a protocol for prion risk patients.
4. Discussion
The local audit showed a very disappointing compliance
with local guidance, as the number of alcohol swabs
identified for only 54% of patient GAT measurements,
assuming the number of alcohol wipes correlates with each
disinfection. Although use of alcohol wipes for tonometer
prism disinfection was not directly observed, the doctors
audited did not recall any other reason for use, and we
believe there were no missed swabs in the count, supporting
the assumption. The results compare poorly to the Aizman
et al. study [4], which showed 100% sterilisation with
alcohol pads. While time constraints in busy clinics and
ignorance of epidemiological principles may have played a
role, these results have been reported to the clinicians, and a
subsequent reaudit 6 months later (again, with clinicians
A. Chandra et al. / Contact Lens & Anterior Eye 31 (2008) 13–16 15
Fig. 2. Methods of tonometer sterilisation used in UK national survey of
ophthalmology departments.
blinded to the audit while it was under way) showed
improved adherence to guidelines.
In the UK national survey, almost a quarter of
departments (23.6%) used disposable tonometer heads
routinely. The remaining three quarters provided reusable
GAT prisms, 60.7% of the departments sampled used
sodium hypochlorite, and 15.7% of departments used
disposable alcohol swabs between patient contacts. Ton-
ometer prisms have been shown to be vectors for
transmission of epidemic keratoconjunctivitis (EKC) [2].
Sterilisation of instrumentation abruptly ends EKC out-
breaks [5]. Soaking GAT prisms in 500 parts per million of
sodium hypochlorite (NaOCl) for 10 min has been shown to
destroy adenovirus 8 [6], herpes simplex, enterovirus 70 and
most bacteria [7]. Wiping tips with swabs impregnated with
70% isopropyl alcohol has also been shown to be effective in
removing adenovirus 8 [6] and most other common ocular
viral and bacterial pathogens [8]. Although Hepatitis C
nucleic acid has been detected on tonometer tips after
sterilisation with wiping with a 70% isopropyl ethanol swab,
it is not thought to confer infectivity [9]. There is therefore
ample evidence that these two methods of sterilisation
are adequate alternatives in routine practice to prevent
transmission of common pathogens. The majority (81.4%)
of departments using hypochlorite confirmed that more than
one tonometer prism was provided per clinician, to allow
adequate exposure to the cleaning solution.
Haag-Streit, the manufacturers of the tonometer prisms
most widely used in the UK, recommends a maximum of
100 uses per prism. However only 7.5% of departments
regularly monitored their tonometer head use, and therefore
followed manufacturer instructions. Although this is most
probably due to the financial implications of regular
tonometer replacement, this low figure may also reflect
ignorance of this guidance.
Regarding prion disease, only 19.3% of charge nurses in
this survey were aware of a departmental protocol in
accordance with RCOphth recommendations that disposable
tonometers are used for any patients at risk of CJD. While
prion disease is rare, and there are no reported cases of prion
disease transmission via GAT, the resistance of prions to
conventional sterilisation methods is the reason for this
cautious advice. Wadsworth et al. [10] found no detectable
concentrations of prion protein in the anterior segments of
eyes from patients with sporadic and variant CJD-appreci-
able concentrations were found only in their retinae and
optic nerves. The risk of transmission via tonometry
therefore seems theoretical, but this survey suggests the
majority of ophthalmology departments have poor knowl-
edge of the guidance regarding those subjects at risk.
Although charge nurses were surveyed in this study, rather
than the medical staff, it seems likely that if the nurse in
charge was unaware of a protocol, then the doctors would
also have been unaware.
In studies of residual epithelial cells on tonometer heads
(which are increased in patients on topical medication), the
biggest reduction is found by wiping the tonometer head
with a tissue which should be performed for all non-
disposable prism GAT, even when using sodium hypo-
chlorite solution [11]. However, importantly, no method
completely removed debris; and therefore none completely
eliminated the risk from transmission of pathogens,
including prion disease.
Desai et al. [12]. showed close agreement between results
using reusable tonometer and disposable prisms. An
alternative method of using a disposable latex cover over
the tonometer head has also been shown to give accurate
results [13]. In busy clinics, this may however impinge
unacceptably on time constraints. Disposable prisms would
therefore seem the preferable alternative.
As has been shown by this survey, there is incomplete
sterilisation of tonometer prisms. Even if carried out, there
is debate as to whether complete elimination of corneal
epithelial debris occurs with any method. In addition,
ophthalmology departments across the UK do not seem to
adhere to manufacturer guidelines for tonometer heads. The
use of disposable prisms currently seems the most effective
method of reducing cross contamination. Although dis-
posable prisms are currently recommended for use in
patients at risk of prion disease, their real benefit may lie in
prevention of transmission of other, more common,
pathogens. The majority of UK ophthalmology training
departments do not seem to have a well-publicized policy for
patients at risk of prion disease. A simpler recommendation
for the use of disposable prisms in all clinical cases may be
easier to follow, and have further reaching benefits. Our
survey has shown that 23.6% of UK training ophthalmic
departments have incorporated such devices in their daily
clinics. Perhaps the rest should follow suit.
References
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