Editor,
In their article Foster et al have addressed an issue of relevance to developing countries that have a high prevalence of angle closure. The likelihood ratio of a positive test using results that we have reported (sensitivity 61.9% and specificity 89.3%) is approximately 6
which is similar to the LR for the authors' 15% cutoff. Invocation of pupillary block to explain the discrepancy seems r...
Editor,
In their article Foster et al have addressed an issue of relevance to developing countries that have a high prevalence of angle closure. The likelihood ratio of a positive test using results that we have reported (sensitivity 61.9% and specificity 89.3%) is approximately 6
which is similar to the LR for the authors' 15% cutoff. Invocation of pupillary block to explain the discrepancy seems reasonable. Twenty-seven percent of our cases do not open following a laser PI2. Technically these patients had plateau iris that could be missed by the limbal chamber depth (LCD). If we were to exclude such cases our LCD sensitivity would be more similar to the authors'.
While our results are similar, we would apply them differently. The authors consider LCD to have two major applications: opportunistic screening in ill-equipped clinics and population based screening. In both
situations they emphasize the need for a high sensitivity, accepting a "certain number" of false positives.
In a developing country, screening in an ill-equipped clinic is quite similar to population based screening. Persons who are test positive will have to travel long distances to seek expert help at centers that are "better." While the goal of screening is identification of pathology (or
eyes at risk), false positives can be a major logistical problem. Six percent of Mongolian eyes were occludable on gonioscopy but only 5-10% of these might actually go on to closure. The positive predictive value of
LCD for the detection of occludable angles is reasonably high, but referral based on LCD alone (which includes false positives) would account for 20% of the population. As denial of treatment, in this case to the
majority and that too after travelling long distances, is undesirable, one
option might be to treat all referred occludable angles. In that case, based on LCD alone, one in five Mongolians would need to travel to obtain
a laser iridotomy that is not necessarily innocuous and one that is probably not needed in the first place. The same logic applies to population based screening but involves even more false positives.
In both situations we would argue for a test with a high specificity and settle for reasonable sensitivity. The sensitivity and specificity of LCD, especially for established ACG is indeed high, but is the specificity
high enough? As table 4 shows the positive predictive value is actually lower for angle closure and angle closure glaucoma as compared to occludable angles. This of course is a function of prevalence, and further emphasizes the need for a high specificity. More so in the case
of occludable angles than established ACG. On the other hand the negative predictive value of LCD is good for most grades (especially grade I).
Hence, at least in a busy clinic situation, a negative LCD can be used to
rule out occludable angles and established angle closure.
A positive LCD on its own doesn't mean very much. However, LCD (LCD greater than or equal to 5%) can be used in conjunction with raised IOP. This would increase the
specificity to about 99% (Specificity for both tests positive = [1-(1-specificity of the first test)(1- specificity of the second test)]. The
sensitivity would decrease as the product of the two test sensitivities but will mainly affect detection of occludable angles, not established
angle closure glaucoma.
If an appropriate test is not available, perhaps we should not screen at all. Certainly with the long-term goal of improving the quality of ophthalmology, teaching gonioscopy to ophthalmologists in developing countries might be a better option. While gonioscopy itself cannot predict which eyes will go into closure, it is the current gold standard;
ophthalmologists in developing countries could be taught this technique with as much ease (or difficulty) as the registrars who used it for the study.
Editor,
We read with interest the Newsdesk piece in the March 2000 issue of the journal, commenting on recent studies indicating a conceptual shift in the understanding of the molecular basis of differential susceptibility to
organ-specific autoimmune diseases. However, we were disappointed that the Newsdesk piece was restricted to studies of the animal model of multiple sclerosis and not that of uveitis....
Editor,
We read with interest the Newsdesk piece in the March 2000 issue of the journal, commenting on recent studies indicating a conceptual shift in the understanding of the molecular basis of differential susceptibility to
organ-specific autoimmune diseases. However, we were disappointed that the Newsdesk piece was restricted to studies of the animal model of multiple sclerosis and not that of uveitis. In a paper published in 1997[1] we demonstrated that ocular-specific antigens (S-Antigen
[arrestin] and interphotoreceptor retinoid-binding protein [RBP]), that are targets for pathogenic autoimmune processes, are expressed in the thymus of certain animals. Furthermore, we found that animals which
express S-antigen or IRBP in their thymus are resistant to experimental autoimmune uveoretinitis induced by the corresponding molecule, whereas the absence of thymic expression correlates with susceptibility.
1. Egwuago CE, Charukamnoetkanok P, Gery I. Thymic expression of autoantigens correlates with resistance to autoimmune disease. J Immunol 1997;159:3109-12.
Editor,
We congratulate Hugh Taylor on his editorial in which he discusses the volume of cataract surgery which needs to be done. We were particularly interested by his calculations drawing attention to the effect of changing the visual threshold at which the decision to undertake cataract surgery is made.
We have reviewed a series of eight audits of cataract surgery to determine the visual acuities a...
Editor,
We congratulate Hugh Taylor on his editorial in which he discusses the volume of cataract surgery which needs to be done. We were particularly interested by his calculations drawing attention to the effect of changing the visual threshold at which the decision to undertake cataract surgery is made.
We have reviewed a series of eight audits of cataract surgery to determine the visual acuities at which patients were put on the waiting list for cataract extraction. The audits were designed to show surgical outcomes but they also list the visions at the point when the decision to operate
was made. They include all patients during short periods between 1982 when intracapsular extraction without lens insertion was the norm and the first six months of 2000 when practically all cases were phacoemulsification through a clear corneal incision with a foldable lens.
They are all based on the throughput of a single firm of a teaching hospital. The table shows visual acuity at listing for cataract extraction.
Audit date
No of cases in audit
Type of surgery
Percentage of patients with a given visual acuity when
decision to operate was taken
6/60 or worse
6/18 to 6/60
6/12 or better
1982
39
ICCE & no lens
76.9
20.5
2.6
1984
68
ECCE & IOL
70.6
25.0
4.4
1988
56
ECCE & PC.IOL
67.9
32.1
0.0
1989
29
ECCE & PC.IOL
62.1
34.5
3.4
1992
23
ECCE & PC.IOL
21.7
69.6
8.7
1998
56
Phaco & IOL
16.1
44.6
39.3
1999
85
Phaco & IOL
14.1
54.1
31.8
2000
41
Phaco & IOL
19.0
33.3
47.7
These results are heartening in that they show that the pool of dense cataracts resulting in visions of 6/60 or worse has decreased (from 77% in 1982 to 19% in 2000). They confirm that as surgical techniques have improved the demand for surgery at an early stage has dramatically increased. In the 1982 audit only 2.6% of cases saw 6/12 or better whereas
by 2000 this figure had risen to 47.7%.
We accept that visual acuity is far from being a comprehensive measure of visual disability but none the less it is useful as an indicator of trends. The trend is clearly towards earlier cataract surgery and it is likely to be maintained resulting in increasing surgical volumes. The answer to Hugh Taylor's question, "How much surgery do we have to do?" is more and still
more. The problem then becomes partly political in that governments decide on maximum waiting times for surgery with the effect that it becomes difficult to prioritise those patients with a serious degree of cataract
over those who are simply suffering inconvenience.
Editor
The article by Forbes et al on cheek mucosa is indeed interesting and helpful in cases of reccurent pterygia, but as they have given irradiation to cases after surgery it becomes a bias as to how much better is cheek mucosa compared with conjunctiva autograft.
Secondly, have they considered the use of buccal mucosa for the same as cheek mucosa is more difficult to harvest although I agr...
Editor
The article by Forbes et al on cheek mucosa is indeed interesting and helpful in cases of reccurent pterygia, but as they have given irradiation to cases after surgery it becomes a bias as to how much better is cheek mucosa compared with conjunctiva autograft.
Secondly, have they considered the use of buccal mucosa for the same as cheek mucosa is more difficult to harvest although I agree that the buccal mucosa is
thicker. I have tried buccal mucosa for severe symblepharons.
Editor,
We read Frau et al's report with interest and noted
that our article in Ophthalmology was not cited as
reference (Larkin G, Flaxel C, Leaver P. Phacoemulsification and silicone
oil removal through a single corneal incision.
Ophthalmology 1998;105:2023-7). In
this article, we reported our experience at Moorfields Eye Hospital with
34 eyes prospectively evaluated to l...
Editor,
We read Frau et al's report with interest and noted
that our article in Ophthalmology was not cited as
reference (Larkin G, Flaxel C, Leaver P. Phacoemulsification and silicone
oil removal through a single corneal incision.
Ophthalmology 1998;105:2023-7). In
this article, we reported our experience at Moorfields Eye Hospital with
34 eyes prospectively evaluated to look at the efficacy and potential
complications of combined cataract extraction and silicone oil removal
with posterior chamber lens implantation. We also reported the method of
Ms Maria Restori, BSc, MSc, MIPSM, Ophthalmic Ultrasound Specialist at
Moorfields Eye Hospital for calculating the IOL power in an oil filled eye
with correction for the specific gravity of silicone oil taken into
consideration.
Our findings were that the procedure was safe and effective for these eyes
that had often had many previous surgeries. The visual outcome in these
eyes was generally good with improvement in visual acuity, even with
recurrent retinal detachment or pre-existing macular pathology. We also
concluded that it was safer to place a rigid posterior chamber implant
after silicone oil removal due to potential contraction of the anterior
capsule limiting the view of the retina post-operatively. Our technique
was a passive technique but might easily be done with the I/A handpiece as
this group reported.
We feel that it would have been appropriate for them to make reference to
our study since it presents a much larger series with more detailed follow-up.
Editor,
I have visited the Kikuyu Eye Unit near Nairobi on a yearly basis since
1992, and have witnessed at first hand both there and in Somalia the
enormous burden of poverty and ill health described and quantified in the
editorial. What strikes me very forcibly is the sheer number of hugely
disadvantaged people. This, and the distressing and widening disparity in
health and income between these peopl...
Editor,
I have visited the Kikuyu Eye Unit near Nairobi on a yearly basis since
1992, and have witnessed at first hand both there and in Somalia the
enormous burden of poverty and ill health described and quantified in the
editorial. What strikes me very forcibly is the sheer number of hugely
disadvantaged people. This, and the distressing and widening disparity in
health and income between these people and those of us living in developed
countries is well made in the editorial. I have come to feel that efforts
at population control should receive a high priority, and in this regard I
was surprised and disappointed that the IHPN makes no mention of this in
their checklist of strategies to reduce the global burden of poverty and
poor health. I would be very interested to hear their response.
Your article is very interesting and indeed very promising as far the management of lymphangiomas is concerned. Do the authors think this drug has any role in the management of capillary haemangiomas or other
vascular abnormalities of the eye?
Editor,
In their article Foster et al have addressed an issue of relevance to developing countries that have a high prevalence of angle closure. The likelihood ratio of a positive test using results that we have reported (sensitivity 61.9% and specificity 89.3%) is approximately 6 which is similar to the LR for the authors' 15% cutoff. Invocation of pupillary block to explain the discrepancy seems r...
Editor,
We read with interest the Newsdesk piece in the March 2000 issue of the journal, commenting on recent studies indicating a conceptual shift in the understanding of the molecular basis of differential susceptibility to organ-specific autoimmune diseases. However, we were disappointed that the Newsdesk piece was restricted to studies of the animal model of multiple sclerosis and not that of uveitis....
Editor,
We congratulate Hugh Taylor on his editorial in which he discusses the volume of cataract surgery which needs to be done. We were particularly interested by his calculations drawing attention to the effect of changing the visual threshold at which the decision to undertake cataract surgery is made.
We have reviewed a series of eight audits of cataract surgery to determine the visual acuities a...
Editor
The article by Forbes et al on cheek mucosa is indeed interesting and helpful in cases of reccurent pterygia, but as they have given irradiation to cases after surgery it becomes a bias as to how much better is cheek mucosa compared with conjunctiva autograft.
Secondly, have they considered the use of buccal mucosa for the same as cheek mucosa is more difficult to harvest although I agr...
Editor,
We read Frau et al's report with interest and noted that our article in Ophthalmology was not cited as reference (Larkin G, Flaxel C, Leaver P. Phacoemulsification and silicone oil removal through a single corneal incision. Ophthalmology 1998;105:2023-7). In this article, we reported our experience at Moorfields Eye Hospital with 34 eyes prospectively evaluated to l...
Editor,
I have visited the Kikuyu Eye Unit near Nairobi on a yearly basis since 1992, and have witnessed at first hand both there and in Somalia the enormous burden of poverty and ill health described and quantified in the editorial. What strikes me very forcibly is the sheer number of hugely disadvantaged people. This, and the distressing and widening disparity in health and income between these peopl...
Your article is very interesting and indeed very promising as far the management of lymphangiomas is concerned. Do the authors think this drug has any role in the management of capillary haemangiomas or other vascular abnormalities of the eye?
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