Sir,

We were interested to read the paper on Ahmed valve implantation in glaucoma secondary to chronic uveitis by Özdal PÇ, Vianna RNG and Deschênes J (Eye 2006; 20: 178–183). We have recently carried out a retrospective audit of 16 eyes that had undergone Ahmed valve (AV) insertion at Stobhill Hospital, Glasgow (May 2001 to September 2004).

Patient demographics, diagnoses, and response to surgery are summarized in Table 1. Mean age was 52.8 years. Ten were female patients and six male patients. The range of follow-up was 12–47 months. Success was defined as postoperative intraocular pressure (IOP) of ≤21 mmHg with or without glaucoma medications and without further surgical intervention at the last visit.

Table 1 Patients' data
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The estimated probability of success at 12 months was 63%, with a 95% CI of 43–91% (Figure 1). The median number of medications pre- and post-AV insertion were 3 and 1, respectively. Four patients with apparently acceptable IOP underwent surgery because of increasing intolerance to medical therapy, especially oral acetazolamide. In two patients, IOP was documented to be higher following AV insertion; however, control was deemed to be adequate on a single topical glaucoma medication. Visual acuity was improved or stable in most of the patients (n=9), five patients lost 1–2 lines and one regained his preoperative vision only after 2 years follow-up. One patient lost 3 lines due to progressive epiretinal membrane. One patient deteriorated from hand movements to no light perception due to progression of her underlying disease (familial exudative vitreoretinopathy).

Figure 1
figure 1

Probability of success over time, based on Kaplan–Meier life-table analysis.

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The early postoperative complications encountered were hyphaema (n=4), hypotony (n=3), and choroidal effusion (n=2).

Overall, AV insertion resulted in a reduction in mean IOP from 26.4 mmHg (SD 7.1) to 18.3 mmHg (SD 7.6) after 12 months. Although our success rate may appear lower than those reported in some other studies,1, 2, 3, 4 comparison with published literature is difficult due to a lack of homogeneity in case mix.5

We agree with the experience of Özdal et al4 that AV appears relatively safe and effective in refractory glaucoma.