The Hydrus is a tiny, pre-curved scaffold made of nitinol, a super-elastic, biocompatible nickel–titanium alloy (about 55% nickel, 45% titanium) widely used in heart stents. Its electropolished surface leaves an inert titanium-oxide layer. It is 8 mm long and shaped to follow the natural curve of Schlemm’s canal — the circular drainage channel of the eye — for about three clock hours.

Rather than a closed tube, it is an open scaffold with alternating spines (for strength) and large windows (through which fluid passes into and along the canal). A short inlet, 1–2 mm long, stays in the front chamber of the eye so that fluid can enter the device. Its open cross-section measures about 292 × 185 µm.¹ It was developed by Ivantis and is now made by Alcon.

The eye constantly makes a clear fluid (aqueous humour) that drains out through a sieve-like tissue, the trabecular meshwork, into Schlemm’s canal and then into small collector channels. In open-angle glaucoma the main resistance lies in the meshwork and the inner wall of the canal, so pressure builds up and slowly damages the optic nerve.

The Hydrus works in two ways at once:

1. Bypass — its inlet lets fluid skip the resistant meshwork.
2. Scaffold — its body props Schlemm’s canal open over about 90°, enlarging it to roughly 4–5 times its normal cross-sectional area. This keeps the canal open and lets fluid reach many more collector channels.

• People with mild-to-moderate open-angle glaucoma (including primary open-angle glaucoma), especially when cataract surgery is planned.
• Patients who want to reduce the number of glaucoma drops, or who find drops difficult to use or tolerate.

It is usually not the right choice for narrow or closed drainage angles, neovascular or inflammatory glaucoma, or advanced glaucoma that needs a very low target pressure — trabeculectomy or a drainage implant may be better there. Because these devices drain into the eye’s natural outflow veins, they cannot lower pressure below about 8 mmHg (the episcleral venous pressure). Your glaucoma specialist decides after examining your drainage angle with gonioscopy, and measuring your optic nerve and visual fields.

1. Assessment. Eye pressure, gonioscopy (to see the drainage angle), OCT scans and visual fields confirm that the Hydrus suits your eye.
2. Anaesthesia. The eye is numbed with drops and/or a local anaesthetic; you are awake but comfortable.
3. Cataract surgery is usually performed first, through a tiny self-sealing incision.
4. Reaching the angle. Under a special gonioscopy lens, the Hydrus delivery cannula is passed through the same incision across the eye to the drainage angle.
5. Placement. The cannula tip enters Schlemm’s canal through the meshwork, and a tracking wheel advances the curved microstent along the canal. The inlet is left in the front chamber.
6. Finishing. The position is checked, the instruments are removed and the incision seals itself — usually without stitches. The Hydrus adds only a few minutes to the operation.

After surgery

• You go home the same day. Vision is often a little blurred for a few days, mainly from the cataract surgery.
• Antibiotic and anti-inflammatory drops are used for a few weeks. Do not stop your glaucoma drops unless your surgeon tells you to — many patients are able to reduce them over the following weeks.
• A little blood in the front of the eye (from the drainage canal) is common for a few days and usually clears on its own.
• Follow-up visits check your eye pressure and healing. Glaucoma needs lifelong monitoring even after successful surgery.

The Hydrus has the longest randomised follow-up of any MIGS device:

• HORIZON trial (556 eyes, Hydrus + cataract surgery vs cataract surgery alone): at 2 years unmedicated eye pressure fell by 7.6 vs 5.3 mmHg, and the average number of glaucoma medicines fell from 1.7 to 0.3 vs 1.7 to 0.7.³
• At 5 years, 66% vs 46% of eyes were still medication-free, and the need for further glaucoma surgery was roughly halved (2.4% vs 6.2%), with no extra loss of corneal endothelial cells.⁴
• HYDRUS II: 80% vs 46% of eyes achieved at least a 20% fall in pressure at 2 years, and 73% vs 38% were medication-free.²
• In the only head-to-head trial (COMPARE, standalone surgery vs two first-generation iStents), the Hydrus achieved more complete success and more medication-free eyes; a Cochrane review estimated about 3 mmHg greater pressure lowering than the first-generation iStent.^5,6

Benefits: no cut in the white of the eye and no bleb, so the conjunctiva is preserved for any future surgery; quick recovery; done together with cataract surgery; fewer glaucoma drops for many patients; and uniquely mature 5-year data.

Possible risks are usually minor and temporary: a small bleed in the front of the eye, a short-lived rise in pressure, or a little iris tissue sticking to the device (peripheral anterior synechiae). Occasionally the device needs repositioning, or further glaucoma treatment is needed later. Serious complications are rare. Nitinol is MRI-conditional — tell the radiographer you have an eye implant.

Both are excellent, safe options with cataract surgery, and the differences between them are small. Your surgeon chooses based on your drainage angle, the stage of your glaucoma and other eye findings. Read about the iStent inject W →

Or call 0712-2595600 / 0712-2595636

1. Samet S, Ong JA, Ahmed IIK. Hydrus microstent implantation for surgical management of glaucoma: a review of design, efficacy and safety. Eye Vis (Lond). 2019;6:32. doi:10.1186/s40662-019-0157-y
2. Pfeiffer N, Garcia-Feijoo J, Martinez-de-la-Casa JM, et al. A randomized trial of a Schlemm’s canal microstent with phacoemulsification for reducing intraocular pressure in open-angle glaucoma (HYDRUS II). Ophthalmology. 2015;122(7):1283-1293. doi:10.1016/j.ophtha.2015.03.031
3. Samuelson TW, Chang DF, Marquis R, et al. A Schlemm canal microstent for intraocular pressure reduction in primary open-angle glaucoma and cataract: the HORIZON study. Ophthalmology. 2019;126(1):29-37. doi:10.1016/j.ophtha.2018.05.012
4. Ahmed IIK, De Francesco T, Rhee D, et al. Long-term outcomes from the HORIZON randomized trial for a Schlemm’s canal microstent in combination cataract and glaucoma surgery. Ophthalmology. 2022;129(7):742-751. doi:10.1016/j.ophtha.2022.02.021
5. Ahmed IIK, Fea A, Au L, et al. A prospective randomized trial comparing Hydrus and iStent microinvasive glaucoma surgery implants for standalone treatment of open-angle glaucoma: the COMPARE study. Ophthalmology. 2020;127(1):52-61. doi:10.1016/j.ophtha.2019.04.034
6. Otárola F, Virgili G, Shah A, et al. Ab interno trabecular bypass surgery with Schlemm’s canal microstent (Hydrus) for open angle glaucoma. Cochrane Database Syst Rev. 2020;3:CD012740. doi:10.1002/14651858.CD012740.pub2
7. Ahmed IIK, Berdahl JP, Yadgarov A, et al. Six-month outcomes from a prospective, randomized study of iStent infinite versus Hydrus in open-angle glaucoma: the INTEGRITY study. Ophthalmol Ther. 2025;14(5):1005-1024. doi:10.1007/s40123-025-01126-x
8. Holmes DP, Clement CI, Nguyen V, et al. Comparative study of 2-year outcomes for Hydrus or iStent inject microinvasive glaucoma surgery implants with cataract surgery. Clin Exp Ophthalmol. 2022;50(3):303-311. doi:10.1111/ceo.14048

Hydrus® is a registered trademark of Alcon. Animations and diagrams are schematic illustrations created by Suraj Eye Institute for patient education and are not to scale. This page is general information and does not replace a consultation.