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The Manor Hospital Beech Rd, Oxford , OX3 7RP
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What is Glaucoma
- What is Glaucoma
- Devices & procedures to manipulate the pressure
- Xen implant
- Endocyclophotocoagulation (ECP)
- Trabeculectomy (‘trab’)
- The irido-corneal angle
- The cornea
- The lens
These bent rays reach the macula and are converted to electrical impulses. This electrical information is sent via the optic nerve to the brain (specifically the visual centre). In this way the information in the environment is sensed as ‘sight’ by our brain. It is easy to see that any insult can disrupt this delicate equilibrium, whether this be in the eye itself or within the brain.
Glaucoma is a disease of the optic nerve, whereby characteristic and often insidious damage leads to progressive irreversible visual field loss. Ultimately the channel between the information accrued in the eye and sent to the brain is lost. There are many theories as to why the nerve is damaged in glaucoma, including compromised blood supply and ‘hormonal’ influences (for further information read this article
However, currently we cannot clinically treat these risk factors, despite active research. Hence the only modifiable risk factor that we can currently treat is pressure within the eye (intra-ocular pressure or IOP).
The eye is composed of fluid: if there was no fluid within the eye it would deflate like a balloon. A beautiful equilibrium exists whereby fluid (called aqueous) is constantly produced and constantly leaves the eye. Since the eye is a contained structure, simple physics traches us that if too much fluid is produced or not enough exits the eye, this equates to increased pressure. This increased pressure is believed to cause damage to the optic nerve in glaucoma. In fact, all the medicine, laser and surgery we offer is to manipulate the IOP.
- A type of laser treatment that is used as an alternative to drops
- The laser is directed at the tissue that drains the fluid from the eye found in the ‘angle’ called the trabecular meshwork.
- The laser is called selective as because the laser only targets tissues containing a specific pigment (melanin).
- In this way, minimal damage to surrounding structures occurs and side effects are reduced. Improved drainage of fluid leads to reduced eye pressure.
- It can take up to 3 months for the lowering of eye pressure to take effect.
- Studies indicate SLT reduces the eye pressure by approximately 30% when used as initial therapy.
- This lowering is comparable to the most commonly prescribed class of glaucoma drops (prostaglandin analogues). The degree to which SLT lowers pressure is influenced by various factors including:
- Age
- Eye pressure before SLT
- Previous glaucoma treatments
- Glaucoma severity.
- SLT usually lasts a few years, but in some cases longer. It can be repeated, however, repeat treatment is less likely to be as effective or successful as the first treatment.
- There is a small chance that this procedure will not lower pressure at all (approximately 20% of patients).
- If SLT doesn’t work, it is likely that eye drops to reduce pressure will be required.
- If SLT doesn’t work, it is likely that eye drops to reduce pressure will be required.
When is it a good option:
- Open drainage angle
- An abundant presence of pigment in the drainage angle
- No previous use of prostaglandin drops
- Minimal optic nerve damage
When is it better to seek other alternatives:
- Closed drainage angle
- Lack of pigment in the angle
- Use of prostaglandin drops
- Advanced glaucoma
- This is a microsurgical drainage implant that enables fluid to drain from within the eye to a space just under the superficial skin of the eye. This creates a filtering ‘bleb
- Unlike traditional glaucoma surgery, scissors and sutures (stitches) are not required.
- The implant itself is a small gelatin tube, 6mm long and as thin as a strand of human hair!
- The gelatin material is not rejected by the body and will not illicit a response
- It is introduced into the correct plane with a special injector, through a self-sealing incision into the clear part of the eye (cornea)
- The procedure with drops alone with your cooperation will help facilitate the safe implantation. You will not feel pain during the procedure.
When is this a good option:
- Patients with
- Early glaucoma &
- Currently on one/two drops &/or
- Requiring cataract surgery
- Patients who already have had cataract surgery & are on one/two drops
When is it better to seek other alternatives:
- Advanced optic nerve damage
- Narrow drainage angles
- Propensity to scar, i.e. certain ethnicities
- A significant proportion of patients (up to 40% in some studies) can develop scarring around the implant, which may necessitate manipulation of the original surgery. With careful and skilful patient selection is key determinant of success.
- ECP is a laser treatment to lower eye pressure and reduce the need for eye drop medications in glaucoma.
- ECP involves the use of a laser probe that targets the part of the eye that produces fluid.
- The laser probe is inserted inside the eye via a tiny incision; usually at the same time as cataract surgery.
- The advantage of ECP is that it allows for direct visualisation of the eye structure needing treatment (ciliary processes), thus improving accuracy and reducing the amount of laser energy required.
- It is performed in the operation room under sterile conditions.
- Oxford University Hospital Trust is a national referral centre: I offer this expert procedure as part of the comprehensive Glaucoma Service.
- The ECP will take up to six weeks to exert its maximal effect, hence you should still continue your glaucoma medication in the operated eye. Any drops you use in your other eye must be continued as normal also.
When is it a good option:
-
- Patients with:
- Early glaucoma &
- Currently on one/two drops &
- Requiring cataract surgery (particularly if the drainage angles are on the narrow side)
- Patients in whom conventional glaucoma surgery will compromise safety, i.e. the skin of the eye is too thin for adequate closure
- Patients who have refractory glaucoma, i.e. full attempts have been made to optimise the outflow of fluid from the eye
- Patients with:
- When is it better to seek other alternatives:
- Propensity to have exaggerated inflammatory response, i.e. history of uveitis
- If you have not had cataract surgery
- This is the most conventional of all glaucoma surgery: as surgeons, we have over 50-years experience in performing and managing trabs
- It is a drainage operation, where a new channel is created for fluid to drain outside the eye into the space immediately under the skin of the eye (creating a bleb similar to the Xen procedure). This is facilitated by the creation of a ‘trap-door’ in the white part of the eye (the ‘sclera’)
- Tip: all surgical interventions in the eye accelerate a cataract formation. In patients with functioning trabeculectomy blebs, do not touch the cataract for ONE year following trab surgery. This is because the inflammation liberated as a consequence of cataract surgery can cause failure of the naïve bleb.
- This long term success of this type of surgery is dictated by the management in the clinic. The surgery must be manipulated in the post-surgical period in the clinic including:
- Potential use of a contact lens to tamponade any micro-leaks that have developed in the skin of the eye (conjunctiva)
- If the pressure is high, the stitches holding the trap door shut down can be either removed by pulling them or being dissolved by laser
- If the skin of the eye begins becoming inflamed, it may require an anti-scarring injection
- If the pressure is very low, the eye is re-inflated with heavy gel injected into the eye
When is it a good option:
- Advanced glaucoma related optic nerve damage or high likelihood to progress to this stage
- High pressures or continual progressive damage despite maximal treatment
- Inability to tolerate medical treatment
When is it better to seek other alternatives:
- High likelihood of failure: particularly if you have a ‘secondary glaucoma’
Aqueous shunt surgery (‘tube’)
- The basic design of every shunt is a silicone tube connecting the anterior chamber inside the eye to a plate, secured in the space underneath the superficial skin of the eye.
- The tube is initially blocked with a large suture inside it’s hollow lumen: if it wasn’t, the fluid of the eye would ‘gush’ out of the tube, causing the pressure in the eye to go dangerously low.
- The plate of the tube develops resistance with time, causing the pressure to go up. Hence around the two-month time frame, the large suture is safely removed in theatre to enable the flow of the tube to be optimal. The plate size I use is either 250 or 350 mm2
- The tube surgery will certainly require a general anaesthetic, as manipulating the muscles in the eye can bring the heart rate down and requires careful management by our Anaesthetic colleagues. Also the surgery is tricky, often lasting an hour, hence general anaesthesia is most comfortable for the patient.
When is it a good option:
- Patients with progressive disease despite optimised medical therapy and a trabeculectomy has either failed or is likely to fail. I.e. the so-called ‘secondary glaucoma’ (which we will look at later).
When is it better to seek other alternatives:
- When general anaesthesia is not an option due to systemic co-morbidities
- The iris (coloured part of the eye)
- The cornea (the outer clear dome of the eye)
If this ‘angle’ is narrow there is a resistance to the flow of fluid outside the eye and hence fluid builds up in the eye: this situation is called ‘chronic narrow angle glaucoma’. Chronic narrow angle glaucoma is more sight threatening than ‘open angle glaucoma’
The angle can only be assessed with a special contact lens in a technique called ‘gonioscopy’: this is performed by a glaucoma specialist. Misdiagnosis is unfortunately common either due to:
- Lack of gonioscopic assessment
- Incorrect interpretation of the assessment
Luckily community optometrists are excellent at referring patients in whom they suspect that the angle may be narrow for gonioscopic assessment by us.
Hence the consequence of a narrow drainage is two fold:
- It can completely close abruptly, leading to no outflow of fluid. The pressure can go up above 70mmHg (normal range between 11 and 21mmHg) leading to:
- Reduced vision
- Pain
- Accelerated optic nerve damage
This is called ‘acute angle closure glaucoma’. The vision can be lost in a matter of hours.
- ‘Sticky bands’ can form within the angle, meaning that the outflow apparatus does not function properly. Hence the pressure insidiously increases, leading to optic nerve damage. This is called ‘chronic narrow angle glaucoma’.
The objective is to open the angle to prevent the sequelae described above. Options to achieve this include peripheral iridotomy or clear lens extraction (see below). Please note: not all patients with narrow angles have high pressure or glaucoma, however it is impossible to predict those who will go onto developing these problems.
- YAG laser uses energy to make a small hole in the peripheral iris, which is too small to be seen with the naked eye.
- The hole can aid in the change of angle configuration in up to 66-76% of patients, to varying degrees.
- Depending on how long the angle has been narrow (or closed) will determine whether the pressure comes down and laser alone is sufficient to manage narrow angle glaucoma. I.e. widening the angle alone may not be sufficient to adequately manage the more advanced cases, necessitating drops or surgery.
When is it a good option:
- Narrow drainage angles
- Excellent unaided vision
- Pre cataract development
When is it better to seek other alternatives:
- Presence of a cataract
- Thick irides
- Previous sever inflammation and a ‘stuck down’ pupil
- Essentially this is cataract surgery despite no cataract being present
- This can be done as a refractive procedure, to circumvent the use of spectacles
- However, in the situation of narrow drainage angles it is a medical procedure to proceed with if:
- The angle remains closed or narrow after laser iridotomy
- Primary treatment for narrow angles
- The rationale behind this is from an eminent recent study that revealed that in the correct patients, if clear lens extraction is performed as the primary procedure there are superior outcomes in terms of:
- Less requirements of further surgical procedures
- Less loss of sight
- The lens is a clear structure that sits just behind the iris near the front of the eye. One of the main reasons people develop angle closure is due to the lens becoming larger causing the iris to move forward.
- By taking the lens out, the iris flops back, ensuring the angle cannot close.
- Once again, by physically opening the angle this does not guarantee adequate pressure control. I.e. widening the angle alone may not be sufficient to adequately manage the more advanced cases, necessitating drops or surgery.
- Caution: the primary aim of the clear lens extraction is to reduce the likelihood of you needing further treatment and/or developing glaucoma in the future. The procedure is not undertaken to reduce your reliance on glasses or to improve vision. In fact, your vision without glasses could be worse after the surgery, necessitating glasses to refine your distance vision.
When is it a good option:
- YAG PI did not adequately open the angle
- Shallow angle and presence of cataract
- Patients motivated by surgery
When is it better to seek other alternatives:
- Excellent unaided vision and reluctance to proceed with surgery
- Very young patients who are yet to wear glasses for reading (pre-presbyopic)