Glaucoma filtration surgery

Glaucoma filtration surgery (trabeculectomyy or non‐penetrating deep sclerectomy) or valve device implantation aims to encourage drainage of the aqueous humour and, therefore, control intraocular pressure by stabilising it for 24 hours and to prevent fluctuations.

We call them filtration techniques because that is exactly what they do: help "filtrate" the intraocular liquid (aqueous humour) as it starts to flow out the eye, creating new ways to drain it.

A decision is usually made to resort to filtration surgery when the patient no longer responds to hypotensive eyedrops or is intolerant to them. 

Surgery is often chosen as the form of treatment when the glaucoma disease is found to be at very advanced stage. At this point, surgery can provide a more stable way of controlling tension, preventing hypertensive peaks (without fluctuations).

Another case would be where laser surgery procedures cannot be used or they are not sufficient. 

Glaucoma filtration surgery (trabeculectomy or non‐penetrating deep sclerectomy) or valve device implantation aims to encourage drainage of the aqueous humour and, therefore, control intraocular pressure by stabilising it for 24 hours and preventing fluctuations.

The most commonly used surgical technique is trabeculectomy. It is called a filtration procedure, because it aims to create a drain or fistula enabling the intraocular liquid or aqueous humour to drain from the eye without any obstacles in the subconjunctival space.

There is also another filtration technique which is an alternative to the trabeculectomy called non-perforating profound sclerectomy. 

One of the most notable differences between the two is that a full operning of the created fistula is not made in the latter technique and, as it is not fully "open" we prevent sudden decompressions. However, a further opening using a laser is usually required in 20-40% of cases. This is normally performed under topical anaesthetic and is an outpatient surgery. In addition, to keeping the drain open, an implant (or sterile material made of different components) is normally used.  

Another surgical technique for glaucoma is the use of glaucoma drainage devices or valve devices, reserved for cases where the techniques above are not advised or cannot be applied. They all need to be performed in an operating theatre under aseptic conditions.

It should be noted that the majority of filtration techniques for the treatment of glaucoma use antiscarring agents that aim to prevent fibrosis and the subsequent closing of the fistula created. The most commonly used are Mitomycin C and Fluorouracil (5-FU). 

The desired result of these surgical techniques is to get the patient's intraocular pressure under control, making it stable all 24 hours of the day and preventing fluctuations. This contributes to the control of the glaucoma disease, stopping it from advancing. 

Furthermore, a large percentage of patients can go without hypotensive drop treatment after surgery, which increases their quality of life.  

These results depend on the type of glaucoma the patient has, the previous anatomical state of the eyeball and the surgical technique used. Not all techniques are equally efficacious, although as in general medicine, none can offer a 100% guarantee of success.

When we talk about glaucoma surgery, the main associated risk is that it involves long-term loss of efficacy. The scarring (the body's power to close wounds) is the main enemy of filtration surgery. This is why the majority of techniques use antiscarring substances to try to reverse the potential any healthy body has to do this. 

Other risks associated with glaucoma surgery are hypotonia due to overfiltration, the appearance of pores in the surgical wound requiring additional sutures or haemorrhages. 

The most significant yet infrequent risks are infections and profuse bleeding.