An anterior chamber intraocular lens (ACIOL) is an intraocular lens fixed to the angle of the anterior chamber in eyes with insufficient support from the lens capsule or zonules (ciliary zonules).
In standard cataract surgery, the intraocular lens is fixed within the lens capsule. However, when capsular support is lost due to intraoperative posterior capsule rupture, zonular dialysis, traumatic lens dislocation, or exfoliation syndrome, alternative fixation methods are needed. ACIOL is one of the long-standing options.
Modern ACIOLs typically have flexible open-loop haptics, with the footplates of each haptic positioned to contact the scleral spur of the anterior chamber angle. Early models were rigid closed-loop designs with many complications, but current open-loop designs have greatly improved outcomes.
When capsular support is insufficient, options for intraocular lens fixation include ACIOL, iris-fixated lenses (iris claw lenses), retropupillary sutured intraocular lenses, and scleral-fixated posterior chamber intraocular lenses 1).
Standard intraocular lenses are fixed within the lens capsule (posterior chamber), while ACIOLs are fixed to the angle of the anterior chamber. They are an alternative fixation method chosen when support from the lens capsule or zonules is lost.
When an ACIOL is appropriately sized and correctly positioned, good visual acuity is often achieved early after surgery. However, if there is size mismatch or malposition, the following symptoms may occur.
When the intraocular lens size is inappropriate, the following findings are observed 1).
Oversized ACIOL
Iris deformation: The haptic compresses the iris, causing distortion of its shape.
Pupil deformation: The pupil becomes oval or distorted.
Corneal endothelial damage: The lens is close to the corneal endothelium, damaging endothelial cells.
Ocular discomfort: Causes persistent discomfort or pain.
Undersized ACIOL
Chronic inflammation: Fixation is unstable, causing lens movement and persistent inflammation.
Cystoid macular edema: Edema occurs in the macula due to ongoing inflammation.
Corneal endothelial damage: Endothelial cells are damaged due to chronic inflammation.
Intraocular lens rotation/dislocation: The lens rotates or dislocates due to insufficient support.
UGH syndrome (Uveitis-Glaucoma-Hyphema syndrome) is a complication caused by mechanical irritation of the iris by an ACIOL. Uveitis, glaucoma, and hyphema appear as a triad, and if left untreated, can lead to corneal endothelial decompensation1).
Additionally, a misplaced ACIOL or an improperly designed intraocular lens placed in the ciliary sulcus can cause persistent intraocular inflammation1). In diabetic patients or those who used pupillary dilation aids during surgery, the risk of persistent postoperative inflammation is high, and the incidence of cystoid macular edema has been reported to reach up to 29.5%1).
It is Uveitis-Glaucoma-Hyphema syndrome. It occurs when an ACIOL mechanically irritates the iris, and the triad appears simultaneously or sequentially. If it progresses, it can lead to corneal endothelial damage1).
The main causes for which ACIOL is indicated and factors that increase the risk of complications are shown below.
In eyes at high risk of corneal endothelial decompensation, caution is also needed in selecting intraocular lens materials other than hydrophobic acrylic 1).
Precise preoperative ocular biometry is essential for proper placement of ACIOL.
Selecting the appropriate ACIOL size is of utmost importance. The main measurement methods are shown below.
| Measurement method | Characteristics | Accuracy |
|---|---|---|
| WTW horizontal diameter | Most standard method | Best option when anterior segment OCT is not available 1) |
| Anterior segment OCT | More accurate anterior chamber width measurement | Most reliable |
| Ultrasound biomicroscopy (UBM) | Detailed observation of anterior chamber structures | Variable consistency |
Horizontal measurement of the white-to-white (WTW) diameter is considered the most accurate method for estimating ACIOL length when anterior segment OCT is not used 1). The common approach is to select a lens that is 1 mm longer than the measured value. However, it is important to note that the optimal length may differ depending on the surgeon’s position (superior vs. temporal).
ACIOL insertion in cases with insufficient capsular support requires meticulous surgical technique.
When capsular support is insufficient, three options for intraocular lens fixation are available: anterior chamber fixation (ACIOL), iris fixation, and intrascleral fixation. A 2018 network meta-analysis supports the effectiveness of all three fixation methods (Evidence level I+, Good, Strong) 1).
Anterior Chamber Fixation (ACIOL)
Design: Flexible open-loop haptics placed in the anterior chamber angle.
Advantages: Relatively simple technique, high durability with PMMA material.
Cautions: Proper size selection affects outcomes.
Iris Fixation
Design: Haptics are directly clipped to iris tissue (e.g., iris claw lens).
Advantages: No need for angle evaluation, applicable to post-vitrectomy eyes.
Cautions: Can be placed anteriorly or posteriorly (retropupillary).
Intrascleral Fixation
Design: IOL haptics are fixed within scleral tunnels (e.g., Yamane technique).
Advantages: Does not use angle or iris, long-term stability expected.
Cautions: Requires conjunctival and scleral manipulation; complications include elevated intraocular pressure and IOL tilt 1).
Incision Creation: Standard ACIOLs are made of PMMA (polymethyl methacrylate) and cannot be folded, so a large incision matching the lens optic diameter (usually 6 mm) is required. To reduce corneal astigmatism, a scleral tunnel incision is often chosen.
Miotic administration: Before insertion, administer miotics such as Miostat (carbachol) or Miochol (acetylcholine) to constrict the pupil. This moves the iris away from the angle and prevents iris entrapment in the haptic loops.
Peripheral iridectomy: To prevent iris bombe due to pupillary block, this must be performed before lens insertion1).
Haptic orientation: The haptics should be placed opposite to the incision site to prevent early haptic prolapse1).
Check for iris entrapment: After insertion, pull each haptic loop centrally and anteriorly to stabilize the lens in the angle. If the pupil is peaked or oval, it indicates iris entrapment and repositioning is required.
In a retrospective analysis (Donaldson et al.), comparing ACIOL and sutured posterior chamber intraocular lenses, no statistically significant differences were found in best-corrected visual acuity or complication outcomes. The final choice of procedure depends on the surgeon’s experience and the patient’s specific anatomical characteristics.
The most standard method is to measure the horizontal white-to-white (WTW) diameter and select a lens that is 1 mm longer than the measured value1). If anterior segment OCT is available, more accurate sizing is possible.
Early ACIOLs were rigid closed-loop types. The haptics continuously compressed and irritated the angle, leading to frequent severe complications such as chronic inflammation, angle damage, corneal endothelial damage, and secondary glaucoma. UGH syndrome was also frequently reported in this era.
Modern flexible open-loop ACIOLs distribute compressive forces on the angle due to the flexibility of the haptics. This design change has significantly reduced complication rates, and outcomes comparable to sutured posterior chamber intraocular lenses have been reported.
Anterior chamber intraocular lenses are more likely to stimulate intraocular inflammation than posterior chamber intraocular lenses, especially when angle anatomy is compromised1). The following mechanisms of inflammation are considered.
Zonulopathy (zonular weakness) is common in uveitis patients and predisposes to the aphakic state requiring ACIOL1).
ACIOLs are closer to the corneal endothelium than posterior chamber IOLs, raising concerns about long-term risk of endothelial cell loss. Even with proper sizing and placement, ACIOLs may lead to faster age-related decline in endothelial cell density compared to posterior chamber IOLs. If corneal endothelial decompensation occurs, corneal endothelial transplantation (DMEK/DSEK) may be required.
The effect of the placement site (anterior vs. posterior) of iris-claw lenses on final outcomes is being investigated1). Whether there are differences in visual outcomes and complication profiles between anterior and posterior placement is a research question, and knowledge is accumulating to individualize surgical technique selection.
The Yamane technique (flange technique) is a sutureless scleral fixation method in which the intraocular lens haptics are fixed within the sclera and the haptic tips are deformed into a flange shape1). It has rapidly gained popularity in Japan, with reported complications including elevated intraocular pressure, IOL tilt, vitreous hemorrhage, cystoid macular edema, conjunctival erosion of the haptic, and endophthalmitis1). Prospective randomized trials directly comparing long-term outcomes of ACIOL and intrascleral fixation are still scarce, and further evidence is needed.
For each fixation method in cases of insufficient capsular support, including ACIOL, long-term comparative studies are needed that include not only uncorrected and corrected visual acuity but also qualitative assessments of visual function such as contrast sensitivity, glare, and halos. Currently, the choice of fixation method largely depends on the surgeon’s experience and the patient’s specific anatomical characteristics.
