Sir,

Case report

We report a case of an unusual ultrasound biomicroscopy (UBM) appearance in a POAG patient at 15 months after receiving non-penetrating trabecular surgery (NPTS). A 37-year-old male received NPTS of the right eye for POAG in a local hospital 15 months ago. After the operation, the IOP was controlled under 15 mmHg. At 14 months, he experienced severe pain in the right eye and blurred vision. Upon examination, the IOP was 50 mmHg, the cornea had oedema, and the pupil was slightly displaced superiorly. After treatment with 20% mannitol, the IOP was controlled and corneal transparency recovered. The gonioscopy examination showed that the iris root adhered to the remanent membrane of NPTS areas. Therefore, a laser iridectomy was performed and 0.005% latanoprost was administered daily, reducing the IOP to 20 mmHg.

The patient then arrived at our hospital for further treatment. Our examination results were as follows: IOP 19.5 mmHg, the bleb of right eye was pale and had a thin wall with darkening of the subconjunctival area, and the pupil decentered. The gonioscopy result showed that the iris root had adhered to the surgical area. The UBM picture is shown in Figure 1.

Figure 1
figure 1

Unusual UBM appearance of bleb and iris after NPTS.

Full size image

Comment

Based on the case history and examination results, we believe that after NPTS, the sudden break of the residual membrane at the operation area resulted in the pressure difference between the upper and lower surface of iris. The iris root was displaced into the bleb through the break and incarcerated, thus blocking the aqueous humor outflow and causing the IOP to rise rapidly, which is one of the complications of NPTS.1

UBM can clearly image the anterior segment of the eye, so it is widely used to evaluate the bleb and to explore the potential reasons for failure of the bleb after NPTS.2, 3 However, in this case, from the UBM picture, we could not identify the iris root location and its relationship with ciliary. In addition, there was a strong reflective cycle in the bleb, which could easily be misinterpreted as a bleb encapsulation. However, an encapsulated bleb would not be associated with an acute increase in IOP, as encapsulation is a slow process. In combination with the supplementary clinical examination results, we concluded that the strong reflective cycle was actually the incarcerated iris. To the best of our knowledge, this exceptional phenomena has not been reported before.

NPTS, which does not enter the anterior chamber during the operation, and in the absence of an iridectomy, would ensure little postoperation inflammation. However, a small percentage of patients were observed with an increasing IOP at prolonged periods after NPTS, which may be due to rupture of the trabeculo-decemet's membrane or adherence of iris root to the membrane.1 These complications, followed up with NPTS, were induced by a consistent existing pressure difference between the upper and lower iris surface after the surgery. Therefore, it is worth considering to perform a laser iridectomy at the surgical area, before the NPTS, as a means of preventing these surgical complications.