Intracameral Injection: Procedure, Uses, and Outcomes

An intracameral injection delivers medication directly into the anterior chamber of the eye, the fluid-filled space between the cornea and the iris. This route bypasses the barriers that limit how much drug actually reaches the inside of the eye when drops are applied to the surface. Eye drops lose the vast majority of their payload to blinking, tear drainage, and the corneal barrier, with studies showing that less than 4% of a topically applied drug typically reaches the aqueous humor.¹ Intracameral injection sidesteps all of that, and its growing list of clinical uses reflects just how much of a difference that directness makes.

How the Injection Is Performed

The procedure itself is quick and typically happens in an operating room or, in some cases, at a slit lamp. The surgeon enters the eye through the clear cornea using a fine-gauge needle, usually 26- or 27-gauge. A temporal approach is preferred when the patient is lying down, since it gives the surgeon a natural angle of entry. The needle is angled bevel-up, tracking through the cornea far enough to create a self-sealing tunnel, and kept well away from the central visual axis and the natural lens. Once inside the anterior chamber, the medication is injected in a controlled, slow push. The needle is then withdrawn gradually, and a cotton-tipped applicator is pressed gently against the wound to prevent fluid from leaking out.²

For antibiotic prophylaxis during cataract surgery, a common protocol involves drawing up a small volume of diluted antibiotic into a tuberculin syringe, then injecting about 0.1 mL into the anterior chamber through the existing paracentesis wound at the end of the case.³ The whole injection step takes seconds. For sustained-release implants like those used in glaucoma, the procedure involves a slightly different inserter device, but the corneal entry pathway is essentially the same.

Why Not Just Use Eye Drops

The bioavailability gap between drops and intracameral delivery is enormous. When researchers have used intracameral injection as a reference standard to measure how much drug actually penetrates the eye from a topical dose, the numbers are striking. In one study comparing topical flurbiprofen to an intracameral dose (which is considered fully bioavailable to the interior of the eye), the topical formulation delivered only about 7 to 10% of the drug to the aqueous humor.⁴ A similar pharmacokinetic study of brinzolamide, a glaucoma drug, found that topical application of a 1% suspension achieved an absolute bioavailability of just 0.10% compared to the intracameral dose.⁵ That means topical drops delivered roughly one-thousandth of the drug to where it needed to be.

This does not mean eye drops are useless. They work well enough for many conditions, and they avoid the need for a needle in the eye. But when you need a high, reliable drug concentration inside the anterior chamber right now, or when a patient cannot be trusted to use drops consistently for months, the intracameral route has clear advantages.

Preventing Infection After Cataract Surgery

Endophthalmitis, a devastating infection inside the eye, is the nightmare scenario after cataract surgery. It is rare even without prophylaxis, but the consequences when it does occur can include permanent vision loss. Injecting an antibiotic directly into the anterior chamber at the end of cataract surgery has become one of the most effective preventive strategies available. A meta-analysis of studies comparing intracameral cefuroxime and moxifloxacin to controls found that both antibiotics reduced endophthalmitis rates with minimal toxicity at standard doses.⁶

Real-world data from a large Indian study put numbers to the effect. After introducing intracameral antibiotics, the rate of acute endophthalmitis after cataract surgery dropped by about 72%, falling from 0.126% to 0.035%. Both cefuroxime and moxifloxacin achieved statistically significant reductions individually, and neither was clearly superior to the other.⁷ By the time surveys of European cataract surgeons were conducted, roughly three quarters reported routinely using intracameral antibiotics, with the vast majority choosing cefuroxime.

The economics reinforce the clinical picture. A cost-effectiveness analysis calculated that intracameral cefuroxime costs about $1,400 per case of endophthalmitis prevented. Topical fluoroquinolone drops would need to be 8 to 19 times more effective than intracameral cefuroxime just to match its cost-effectiveness, depending on which drop was used.⁸ A systematic review confirmed that intracameral cefuroxime showed the best cost-effectiveness ratio among available prophylaxis regimens.⁹

Pupil Dilation During Cataract Surgery

Cataract surgery requires a wide, stable pupil so the surgeon can see and access the lens. Traditionally, this is achieved with a series of dilating drops given over 30 to 60 minutes before the procedure. An intracameral combination of mydriatics (pupil-dilating agents) and anesthetic offers a dramatically faster alternative. In one study, 95% of pupil dilation occurred within a mean of about 29 seconds after the intracameral combination was delivered.¹⁰

Speed is not the only benefit. The intracameral approach also held the pupil more stable throughout surgery. In the group receiving the intracameral combination, the pupil shrank by less than a millimeter between the start and the end of surgery in nearly 90% of eyes. Only about 27% of eyes in the topical-drop group managed the same stability. Patients receiving the intracameral combination also spent significantly less time in the preoperative and surgical areas combined, averaging roughly 23 minutes compared to about 49 minutes for the topical-drop group.¹¹ For busy surgical centers running many cases per day, that time difference is substantial.

Sustained-Release Implants for Glaucoma

Glaucoma is a chronic disease that typically demands daily eye drops for years or decades, and adherence to those drops is notoriously poor. Many patients forget doses, struggle with the physical act of instilling drops, or experience surface irritation that makes them want to stop.¹² The idea behind intracameral sustained-release implants is simple: put the drug inside the eye once and let it release slowly over months, removing the patient from the compliance equation entirely.

The first product to reach the market was a biodegradable bimatoprost implant (Durysta), which is injected into the anterior chamber and gradually releases bimatoprost, a prostaglandin analog. It provides pressure-lowering effects comparable to daily prostaglandin eye drops, with the advantage that the patient does not need to do anything after the procedure.¹³ A meta-analysis comparing intracameral prostaglandin implants found that bimatoprost implants achieved mean pressure reductions of about 6 to 7 mmHg at 12 months. Travoprost-based implants under development showed somewhat variable results depending on the study, though they were broadly comparable to the lower-dose bimatoprost implant at shorter follow-up periods.¹⁴

An 18-month real-world study tracked patients who received the bimatoprost implant in routine clinical practice. Pressure reductions ranged from 1 to 2 mmHg on average across follow-up visits, and an estimated 78% of eyes required no additional medication for pressure management throughout the study period.¹⁵ Patients also used fewer daily eye drops after the implant. On average, they reduced their drop burden by about half a medication at the 12-month mark compared to baseline.¹⁶

Corneal Endothelial Cell Concerns with Implants

The corneal endothelium, a single layer of cells on the inner surface of the cornea, does not regenerate in humans. Any procedure that involves placing something inside the anterior chamber risks damaging these cells, and intracameral implants sit in close proximity to them for months. This is one of the more carefully watched safety endpoints for sustained-release glaucoma devices.

In the ARTEMIS 2 phase 3 trial, eyes receiving the 10 µg bimatoprost implant lost about 5% of their corneal endothelial cells by 20 months, compared to roughly 1% in eyes receiving topical timolol drops. The higher 15 µg dose caused more corneal complications, including endothelial cell loss and corneal edema, particularly after repeated administrations.¹⁷ A separate phase 3 trial comparing the implant to selective laser trabeculoplasty found a mean endothelial cell loss of about 6% in implant-treated eyes at 24 months, versus about 3% in laser-treated eyes, with the fixed readministration group losing closer to 8%.¹⁸

For most patients, a few percent of cell loss over a couple of years is manageable since there is a large functional reserve. But repeated implantation over many years could accumulate losses that matter, and clinicians are understandably cautious about long-term use in younger patients or those with pre-existing endothelial compromise.

Clearing Fibrin Clots and Treating Abnormal Blood Vessels

Intracameral injection is not limited to prophylaxis or chronic disease management. It is also used as a rescue therapy when things go wrong inside the eye. One classic example is injecting tissue plasminogen activator (tPA), a clot-dissolving enzyme, to clear fibrin or blood clots that form in the anterior chamber after surgery or in eyes with glaucoma drainage devices.

In a series of 36 eyes with valved glaucoma implants that developed tube occlusion from fibrin or blood, intracameral tPA successfully cleared or prevented the blockage in about 89% of cases. The average pressure drop 24 hours after the injection in eyes with fully occluded tubes was dramatic, falling by roughly 21 mmHg. Complications, including severe bleeding, low pressure, and chamber flattening, occurred after about 11% of injections.¹⁹ A separate study using a low-dose tPA protocol for fibrinous membranes found that 84% dissolved within 2 to 12 hours, with complete resolution in all cases by 3 days and no hemorrhagic complications.²⁰

Abnormal new blood vessels growing on the iris, a condition called rubeosis iridis often driven by diabetes or retinal vein occlusion, can also be targeted with intracameral anti-VEGF drugs like bevacizumab. Injecting bevacizumab directly into the anterior chamber in a small series of eyes with iris rubeosis showed decreased leakage from the abnormal vessels as early as one day after injection, with no relapse seen within a four-week follow-up.²¹ In neovascular glaucoma, the pressure-lowering effect of intracameral bevacizumab appeared within a week but was limited to about three weeks on average, buying time for additional procedures like laser or surgery that offer more durable control.²²

Controlling Inflammation After Surgery

Some surgeons inject a steroid directly into the anterior chamber at the end of cataract surgery to get a head start on controlling postoperative inflammation. A study comparing intracameral dexamethasone to intracameral triamcinolone found both equally effective at suppressing inflammation in the first day after surgery. However, the triamcinolone group had higher eye pressure on postoperative day one, likely due to the particulate structure of the drug. The highest recorded pressure in that group was 24 mmHg, which resolved within days, but the authors noted this could matter in patients with glaucoma, making dexamethasone the preferable choice for those individuals.²³

Fungal Infections

Fungal keratitis, a corneal infection caused by organisms like Fusarium or Aspergillus, can be extraordinarily difficult to treat. Standard topical antifungal drops penetrate poorly, and some infections progress despite aggressive topical therapy. Intracameral voriconazole injection has emerged as a treatment option for cases that resist conventional therapy. In a series of 10 eyes with fungal endophthalmitis spreading from corneal infections, intracameral voriconazole injections showed promising results.²⁴ Another study found intracameral voriconazole had similar therapeutic effect to intracameral amphotericin B, but with a potentially better safety profile for the delicate intraocular tissues.²⁵

In particularly stubborn cases, combining intracameral with intrastromal injection, where the drug is placed directly into the corneal tissue, has shown benefit. A case report of recalcitrant Acremonium keratitis described marked improvement beginning three days after this combined approach, with the result sustained through six months of follow-up.²⁶

Risks and Complications

Intracameral injection is generally safe when done properly, but the margin for error is narrow because the anterior chamber is a small, enclosed space. Dosing accuracy matters enormously. Laboratory work has shown that cefuroxime concentrations above a certain threshold cause significant damage to corneal endothelial cells, and the safety window between a therapeutic dose and a toxic one is not wide.²⁷ A case of severe anterior segment toxicity was reported after undiluted, high-volume moxifloxacin was injected intracamerally, a dosing error that caused a condition known as toxic anterior segment syndrome, or TASS.²⁸

TASS is the complication that gets the most attention because it can mimic an infection while actually being a sterile inflammatory reaction, often caused by incorrect drug concentration, contaminated solutions, or residual detergent on instruments. It typically presents within 24 hours of surgery with diffuse corneal edema and anterior chamber inflammation.

Pressure spikes are another risk. In one case, a viscoelastic substance (Healon 5) injected intracamerally to support the anterior chamber after a glaucoma procedure caused pressure to spike to 70 mmHg within 12 hours. Emergency washout of the viscoelastic resolved the problem rapidly, with the pressure dropping to 14 mmHg and vision recovering to near-normal.²⁹ Preservatives commonly found in ophthalmic solutions can also cause damage if injected intracamerally. Benzalkonium chloride, a preservative used in many eye drops, causes dose-dependent endothelial toxicity when placed directly inside the anterior chamber, which is why preservative-free formulations are critical for intracameral use.³⁰

Emerging Frontiers in Cell Therapy

One of the more experimental applications of the intracameral route involves injecting cultured human corneal endothelial cells to treat bullous keratopathy, a painful condition caused by endothelial failure. Because these cells do not regenerate on their own, the standard treatment has historically been a corneal transplant. A recently described technique uses a long, tangential corneal tunnel created with a 26-gauge needle to inject cultured cells into the anterior chamber, where they can settle on the inner corneal surface and potentially restore function.³¹ If this approach matures, it could transform the treatment of corneal endothelial disease by replacing surgery with a brief injection, dramatically expanding access for patients in regions where donor corneas are scarce.