Mon-Fri: 9am - 5pm, Sat: 9am - 1pm

Dr. Chelvin Sng: Why Paul Glaucoma Implant is changing the future of Glaucoma

Glaucoma is the leading cause of blindness in the world. It is an irreversible chronic disease that affects children and adults; globally, the number of glaucoma patients is expected to increase by 74% by 20401

In Singapore, nearly 10% of people over the age of 70 have glaucoma2. Considering how glaucoma is largely symptom-free and is hence touted as the “silent thief of sight”, I believe that we still have many unreported cases amongst us. 

Unfortunately, many people are still losing vision from glaucoma. 

The current mainstay for glaucoma treatment includes eye drops, the success of which highly depends on patient compliance. Furthermore, the patient must adhere to this treatment for life. 

If glaucoma eye drops do not lower the eye pressure sufficiently, or if the patient is unable to use the eye drops regularly, conventional glaucoma surgery including trabeculectomy is an option. Trabeculectomy is effective in lowering eye pressure but may be associated with blinding complications including a life-long risk of infection

Another lesser-known surgical alternative is glaucoma tube implants, which have been used to treat severe glaucoma in the past 30 years with much success. However, until recently, the options for tube implants were limited and the commonly used tube implants were invented more than 20 years ago. 

It is time that we take advantage of the advanced technological advancements to develop newer, more effective and safer tube implants for the benefit of our glaucoma patients. 

In 2012, my colleague Professor Paul Chew and I, together with a team of clinician-scientists from the National University Health System, started developing a new tube implant – the Paul Glaucoma Implant (PGI). The goal was to create an implant that is better than currently available devices — and we sure did. 

Today, the PGI is used in 17 countries worldwide and has greatly improved many patients’ quality of life. Read all about it in this Straits Times feature. 

In this article, allow me to explain what glaucoma tube implants are, how the Paul Glaucoma Implant fares against current choices and why I believe this new invention will greatly change the treatment landscape for glaucoma. 

What are glaucoma tube implants? 

With glaucoma, the fluid within the eye does not drain properly. This results in elevated eye pressure (or intraocular pressure) which damages the eye nerve, eventually leading to blindness if untreated

Hence, the only effective way to treat glaucoma is to reduce eye pressure

Glaucoma tube implants are devices placed in the eye to allow fluid to drain out of the eye. This helps lower eye pressure and prevents further damage to the eye nerve. 

There are a few types of glaucoma implants out there, but regardless of which implant is used, it should be noted that the implants do not improve vision. Instead, they are used to lower eye pressure and prevent further vision loss from glaucoma

When are glaucoma tube implants used?

Glaucoma tube implants are typically used in situations such as: 

  • Severe and complicated glaucoma 
  • Injuries to the eye 
  • Childhood glaucoma 
  • Neovascular glaucoma 
  • If non-surgical alternatives and other surgeries have not worked 

Current types of glaucoma tube implants in Singapore

All tube implants have a smaller tub attached to a larger plate. 

There are two types of glaucoma implants — valved and non-valved. Respectively, the two most commonly used tube implants are the Ahmed Glaucoma Valve (AGV) and the Baerveldt Glaucoma Implant (BGI). The Baerveldt implant has a larger plate compared with the Ahmed implant (350mm2 vs 184mm2). 

The option you choose depends on a few factors, including the severity of your condition and whether you’ve had surgical interventions in the past

In terms of results and efficacy, comparison studies3 have found that the Baerveldt has a lower failure rate but significantly higher risk4 of hypotony (low eye pressure). The superior efficacy of the Baerveldt implant is thought to be related to its larger plate size. While the valve mechanism of the Ahmed decreases the risk of postoperative complications, it is less effective in lowering the eye pressure compared with a Baerveldt tube4,5

There is a need for a glaucoma tube implant with similar efficacy to the Baerveldt but with a reduced complication rate, hence the Paul Glaucoma Implant was developed. 

How does the Paul Glaucoma Implant work? 

Like the Ahmed and Baerveldt tubes, the PGI is an aqueous shunt designed to reduce eye pressure. It can be used for patients with: 

  • Medically uncontrolled glaucoma 
  • Previous failed glaucoma surgery
  • Secondary glaucoma, including neovascular, uveitic and traumatic glaucoma

The tube size of the PGI (0.1mm) is smaller compared to the Baerveldt and Ahmed tubes (0.3mm). The smaller tube size of the PGI is likely to decrease the risk of complications, including tube exposure, cornea damage and hypotony (low eye pressure)

The plate size of the PGI is similar to the Baerveldt implant and larger than the Ahmed implant, hence it is likely that the efficacy of the PGI is similar to the Baerveldt and better than the Ahmed. 

Why was the Paul Glaucoma Implant created? 

PGI was created with one aim in mind — to design an implant that can achieve better outcomes for our glaucoma patients. After years of tireless research, we can now answer these pertinent questions: 

Does this implant have a higher success rate and lower complication rate than existing tube implants? 

In the clinical trials6 we conducted to study the efficacy of PGI one year after implantation, 93.2% achieved qualified success. 68.9% saw complete success. These results suggest that efficacy of the PGI is similar to the Baerveldt Glaucoma Implant and better than the Ahmed Glaucoma Valve, with a higher safety profile than the Baerveldt Glaucoma Implant.

Is it surgically easier to insert? 

The surgical technique for implanting the PGI is similar to the Baerveldt implant, with a higher level of complexity compared with the Ahmed Glaucoma Valve. Hence, it is important to find a surgeon who is skilled and trained in implanting the PGI to perform the surgery. 

Is it self-regulating to prevent too much or too little aqueous flow? 

Aqueous flow through the PGI is regulated with an internal suture in the lumen of the tube, so as to prevent the eye pressure from going too low in the early postoperative period. Subsequently, your surgeon will be able to increase the flow through the implant by removing this suture. With meticulous monitoring and management, your surgeon can titrate flow through the PGI after the surgery. 

Can it control eye pressure over time? 

In a study7 conducted at the Manchester Royal Eye Hospital in the UK, 90.1% were qualified successes and achieved an IOP of >5 a year later without the need for medication. I have patients whose eye pressure is still well-controlled (often without glaucoma medications!) a few years after implanting the PGI.

Mean IOP one year post-operation13.2±3.316.57±3.3514.76±2.5

Importantly, can it improve the patient’s quality of life, eliminating the need for eye drops and future glaucoma surgeries? 

The same study found that the mean number of medications dropped from 3.61 ± 1.09 to 1.22 ± 1.21 post-operation. 

What are the risks of Paul Glaucoma Implant? 

As with other implants, potential postoperative complications include; 

  • Hypotony 
  • Tube occlusion 
  • Shallow anterior chamber 
  • Choroidal effusion 

However, your chances of getting side effects are highly dependent on factors like the severity of the condition and the skill of the surgeon. 


Every day, glaucoma is still robbing patients of their vision. While we still need safer and more effective surgical options for glaucoma, with newer devices like PGI developed with intelligent technology and improved surgical outcomes, I believe this puts us a few steps forward and gives us hope of preserving the vision of millions of glaucoma patients worldwide. 

If you have any questions regarding the condition or surgery, please feel free to drop me a message and I am more than happy to help. 


  1. Sng, C., Harasymowycz, P., & Barton, K. (2017). Microinvasive Glaucoma Surgery. Journal of ophthalmology, 2017, 9845018.
  3. Christakis, P. G., Kalenak, J. W., Tsai, J. C., Zurakowski, D., Kammer, J. A., Harasymowycz, P. J., Mura, J. J., Cantor, L. B., & Ahmed, I. I. (2016). The Ahmed Versus Baerveldt Study: Five-Year Treatment Outcomes. Ophthalmology, 123(10), 2093–2102.
  4. Sng, C., Wang, J., & Barton, K. (2017). Caution in Using the XEN-augmented Baerveldt Surgical Technique. Journal of glaucoma, 26(11), e257.
  5. Riva, I., Roberti, G., Oddone, F., Konstas, A. G., & Quaranta, L. (2017). Ahmed glaucoma valve implant: surgical technique and complications. Clinical ophthalmology (Auckland, N.Z.), 11, 357–367.
  6. Koh, V., Chew, P., Triolo, G., Lim, K. S., Barton, K., & PAUL Glaucoma Implant Study Group (2020). Treatment Outcomes Using the PAUL Glaucoma Implant to Control Intraocular Pressure in Eyes with Refractory Glaucoma. Ophthalmology. Glaucoma, 3(5), 350–359.
  7. Vallabh, N. A., Mason, F., Yu, J., Yau, K., Fenerty, C. H., Mercieca, K., Spencer, A. F., & Au, L. (2021). Surgical technique, perioperative management and early outcome data of the PAUL® glaucoma drainage device. Eye (London, England), 1–6. Advance online publication.

Contact us

Schedule an appointment if you have any questions

    Dr Chelvin Sng of Chelvin Sng eye center

    Dr Chelvin Sng

    Adjunct Associate Professor
    Senior Consultant Ophthalmologist
    ✓ 4 Gold Medals (Specialist Accreditation Examination)
    ✓ "Top 50 Rising Stars” (2017), “Top 100 Female Ophthalmologists” (2021)
    and "Top 100 Ophthalmologists" (2022)
    ⋆ Global Ophthalmologist Power List (voted by peers worldwide)
    ✓ Cambridge University Graduate with Triple First Class Honours and Distinctions


    38 Irrawaddy Road Mt Elizabeth Novena Specialist Centre, #06-25, Singapore 329563

    Operating Hours

    Mon - Fri: 9am - 5pm
    Saturday: 9am - 1pm
    Sunday / PH: Closed