Ординатура / Офтальмология / Английские материалы / Glaucoma Surgery_Trope_2005

Such sites are indicated by a gap in the surgical incision site internally, possibly combined with a shallow bleb at the surgical site. Cyclodialysis caused by surgical procedures can be imaged as a separation of the ciliary body from the scleral spur (22) and the extent of the dialysis measured (Fig. 13.11). In patients with inflammatory conditions, ciliary body membranes can be detected if present, and their relationship to the ciliary processes and presence of traction ascertained.

4.7.Malignant Glaucoma

The ultrasound biomicroscopic appearance in the acute stage of malignant glaucoma shows several distinct features. The ciliary processes and iris are rotated forward closing the angle. The chamber is extremely shallow with the anterior position of the lens (Fig. 13.12). A supraciliary effusion is present (Fig. 13.13). We have previously shown that supraciliary effusions are found by ultrasound biomicroscopy (23), and postulated that effusions may have a major role in the clinical presentation of malignant glaucoma. We have subsequently examined a number of patients with malignant glaucoma and found supraciliary effusions, in the majority, in the acute phase. Other authors have reported similar findings (24).

Supraciliary effusions can occur in other settings such as venous obstruction (e.g., vein occlusions and retinal detachment surgery) and following inflammatory episodes (25 28). Some of these patients develop angle closure glaucoma characterized by shallow anterior chambers. Ultrasound biomicroscopy in these cases shows effusions with anterior rotation of the ciliary processes and iris. This is identical to the ultrasound biomicroscopic appearance in cases of malignant glaucoma. The clinical presentation is essentially identical to that of malignant glaucoma with shallow or flat anterior chambers. Medical treatment that includes hypotensive agents and cycloplegics is the same.

The similarity of the clinical presentation of malignant glaucoma and effusion-based glaucoma has been noted in the past. These two entities, however, have been divided essentially by the presence or absence of an effusion as detected by the methods available at the time. If the effusion was not detected by clinical or B-scan examination, then the clinical case was assumed to be caused by aqueous misdirection. The increased precision of ultrasound biomicroscopy in detecting these effusions forces us to reassess our classification of these entities (29).

Further clinical research will be required in future to fully verify these mechanisms. Ultrasound biomicroscopy will be an important tool as it is the only method available at this time that consistently detects small effusions. A greater understanding of the sequence of events in malignant glaucoma should lead to an improved treatment approaches.

5.CONCLUSION

Ultrasound biomicroscopy allows subsurface imaging of various sequelae in glaucoma surgery. This imaging method can be helpful in determining the cause of underfiltration and overfiltration, and in the diagnoses and follow up of complications.

REFERENCES

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11.McWhae JA, Crichton AC. The use of ultrasound biomicroscopy following trabeculectomy. Can J Ophthalmol 1996; 31(4):187 191.

12.Avitabile T, Russo V, Uva MG, Marino A, Castiglione F, Reibaldi A. Ultrasound biomicroscopic evaluation of filtering blebs after laser suture lysis trabeculectomy. Ophthalmologica 1998; 212(suppl 1):17 21.

13.Martinez Bello C, Rodriguez Ares T, Pazos B, Capeans C, Sanchez Salorio M. Changes in anterior chamber depth and angle width after filtration surgery: a quantitative study using ultrasound biomicroscopy. J Glaucoma 2000; 9(1):51 55.

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15.Ito K, Matsunaga K, Esaki K, Goto R, Uji Y, Supraciliochoroidal fluid in the eyes indicates good intraocular pressure control despite absence of obvious filtering bleb after trabeculect omy. J Glaucoma 2002; 11(6):540 542.

16.Chiou AG, Mermoud A, Underdahl JP, Schnyder CC. An ultrasound biomicroscopic study of eyes after deep sclerectomy with collagen implant. Ophthalmology 1998; 105(4): 746 750.

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21.Sicco thoe Schwartzenburg GW, Pavlin CJ. Occult wound leak diagnosed by ultrasound biomicroscopy in patients with post operative hypotony. J Cataract Refract Surg 2001.

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Section II: Management of Complications

and the anterior chamber formed, the most likely diagnosis is an encysted bleb. Another possibility is that the bleb is formed with something other than aqueous, for example, viscoelastic. If the anterior chamber is formed, intraocular pressure high, and the bleb flat, then aqueous is not flowing through the trabeculectomy either because the scleral-flap sutures are too tight or there is a physical blockage to filtration, such as blood, iris, or vitreous in the osteium. Gonioscopy will exclude vitreous in the osteium. If the osteium is clear, then digital ocular massage will usually establish the flow of aqueous around the flap edges and lower the intraocular pressure. If ocular massage is unsuccessful, then suture lysis or release is the next step.

1.2.Formed Anterior Chamber and Low Intraocular Pressure

Continuing on the left side of Fig. 14.1, the next group of scenarios involves a formed anterior chamber and low intraocular pressure. Again, the knowledge of the bleb status will lead to the correct diagnosis. In the case of a formed anterior chamber, low intraocular pressure, and a formed bleb, the diagnosis is overfiltration (,4 mmHg) or the expected outcome (if the intraocular pressure is within the target range). In the case of a formed anterior chamber, low intraocular pressure, and a flat bleb, one must carefully look for a conjunctival wound leak. In the absence of a leak, the diagnosis is aqueous shutdown.

1.3.Shallow/Flat Anterior Chamber and High Intraocular Pressure

Proceeding with the right side of Fig. 14.1, with a shallow/flat anterior chamber, the next point of differentiation is the intraocular pressure. In the case of a shallow/flat anterior chamber and an elevated intraocular pressure, funduscopy will diagnose a suprachoroidal hemorrhage. The clinical presentation of a suprachoroidal hemorrhage is usually dramatic and will also include severe pain. In the absence of a suprachoroidal hemorrhage one must determine whether the iridectomy is patent. In the case of a shallow/flat anterior chamber, elevated intraocular pressure, normal funduscopy, and absence of a patent iridectomy, the most likely diagnosis is pupil block. In the presence of a shallow/flat anterior chamber, elevated intraocular pressure, no suprachoroidal hemorrhage, and patent iridectomy, the diagnosis is aqueous misdirection. It is important to understand that an elevated intraocular pressure in the scenario of a shallow/flat anterior chamber could be 8 mmHg. The causes of a flat anterior chamber are either hypotony or posterior pressure. For hypotony to be the cause of a shallow/flat anterior chamber, the intraocular pressure should be ,4 mmHg. If the anterior chamber is shallow/flat and the intraocular pressure is

.4 mmHg one should consider posterior pressure, such as aqueous misdirection, pushing the iris lens diaphragm forward creating a shallow/flat anterior chamber. The diagnosis of early aqueous misdirection can be easily missed when the intraocular pressure is in the single digits.

1.4.Shallow/Flat Anterior Chamber and Low Intraocular Pressure

The definition of a low intraocular pressure which is unable to maintain an anterior chamber is usually ,4 mmHg. A possible exception occurs when the anterior chamber is flat, with lens corneal touch, where tonometry can be inaccurate. When the anterior chamber is shallow/flat and the intraocular pressure is low, the next assessment is the filtration bleb. The combination of a shallow/flat anterior chamber, low intraocular pressure, and formed bleb is consistent with overfiltration. In the case of a shallow/flat

anterior chamber, low intraocular pressure, and shallow/flat bleb one must carefully look for a wound leak. In the absence of a leak, funduscopy or a B scan will likely reveal a choroidal.

Using this algorithm, the diagnosis of an early postoperative complication following trabeculectomy surgery is simplified. The following chapters will deal with the diagnosis and management of these and other complications in detail.