Managing eyes at the extremes of axial length (AL)—longer than 26 mm or shorter than 20 mm—presents unique anatomical and surgical challenges during phacoemulsification. This article summarizes key considerations for biometry and intraocular lens (IOL) calculations, chamber stability, and the selection of minimally invasive glaucoma surgery (MIGS) procedures in these complex cases.

The crux of the matter, and the key to managing any eye whether long or short, is understanding the dynamic relationship between the iris, the lens-capsule complex, and the hyaloid face (Figure 1). A short eye will tend to push forward, with fluid being directed behind the iris and/or between the posterior capsule and hyaloid face (aqueous misdirection), pushing the entire capsular complex forward, shallowing the anterior chamber, and causing iris prolapse. A long eye will have a larger volume of anterior chamber, an iris prone to posterior bowing, and bouncy zonules. This leads to overfill of the anterior chamber, pushing the iris back toward the anterior lens capsule, causing posterior pupillary block due to a posteriorly bowed iris, pushing the whole capsular complex posteriorly stressing zonules.

Considerations in Biometry and IOL Calculations for Long Eyes (>26 mm)

Artifacts in AL measurement need to be considered for long eyes. Staphylomas may cause macular dragging or distortion, and manual A-scan biometry may be less accurate than fixation-based methods in these eyes, where the patient guides the measurement. Additionally, adjustments for axial lengths longer than 26 mm need to be used with certain formulas to prevent error in IOL power calculation. The Koch/Wang formula (Adj AL = 0.8289 × IOLM AL + 4.2663) gives a more accurate “effective” AL, which can then be used with the Holladay 1 formula to predict lens power more accurately in long eyes. Newer generation formulas, like the Barrett, tend to be more accurate for longer lengths without a specific adjustment. Additionally, corneal measurements can be a source of error if the patient had prior refractive surgery, is a long-term contact lens wearer, or possibly forgot to remove a contact lens before the corneal measurements are taken. Surgeons may need to special order lenses like the MA60MA or MN60MA (Alcon), available in ±5D ranges.

Chamber Stability

Long eyes often exhibit posterior pupillary block as the iris margin pushes down onto the anterior capsule, trapping fluid in the anterior chamber. In general, all tissue in longer eyes exhibits some level of “floppiness”—iris, zonules, wound, and retina—requiring careful fluidics and wound management, with low threshold for suturing the wound to ensure tight closure. Longer eyes have higher risk for retinal detachment, and this should be discussed with the patient preoperatively. Dilated exams can be performed postoperatively at month 1, 6, and 12, then annually.

MIGS Options for Long Eyes

Most MIGS options can be used at the time of phaco in a longer than average eye, including goniotomy using an instrument like the Kahook Dual Blade (New World Medical), gonioscopy-assisted transluminal trabeculotomy (GATT) using a suture or something like the Omni surgical system (Sight Sciences), ab interno canaloplasty (ABiC), trabecular bypass using Hydrus Microstent (Alcon) or iStent (Glaukos), or Xen gel stent (AbbVie). Considerations for MIGS procedures in longer eyes include device length and placement challenges due to increased circumference of Schlemm’s canal or a flatter radius of curvature which may cause stents to poke through at the distal tip. For stent cases in longer eyes, it can be helpful to leave the stent a little underdeployed to prevent this, assuming that there is adequate space between the iris and the inlet of the device. The “floppiness” of a long eye can complicate visualization due to an underinflated anterior chamber and too much corneal compression under the goniolens. Additionally, there is an increased risk of hypotony with filtration procedures.

Biometry and IOL Calculations for Short Eyes (<20 mm)

Shorter eyes are prone to myopic surprises due to effective lens position (ELP) errors. The myopic surprise may be transient or permanent depending on the cause. Short eyes are more susceptible to aqueous misdirection, both intraoperatively and postoperatively. A myopic surprise in a short eye may indicate a subacute aqueous misdirection due to an anteriorly shifted IOL, even with normal eye pressure. A nice way to test (and treat) this issue is to atropinize the patient and see if the IOL plane shifts posteriorly as the myopia resolves. In eyes with a plateau iris configuration, the ciliary body is rotated forward, which causes the IOL to sit more anteriorly than predicted by the formulas. This will not resolve with atropinization because there is no component of aqueous misdirection. Treatment of aqueous misdirection postoperatively may involve atropinization, a YAG laser to the posterior capsule/hyaloid face, or a trip back to the OR for an iridozonulohyaloidectomy.

High-power IOLs like SA60AT (Alcon; up to 40D) or CT Lucia (Zeiss; up to 34D) may be needed in shorter eyes. Although piggyback IOLs are tempting, your local glaucoma surgeon would urge you to avoid them in favor of hyperopic contact lenses or glasses.

Key Consideration for Phacoemulsification

Keeping a stable anterior chamber is the key to getting in and out of short eyes without trouble. Short eyes have tight anterior chambers, floppy irides after laser peripheral iridotomy (LPI), and weak zonules. A tendency toward intraoperative bombe and misdirection will only aggravate the issue and can quickly complicate surgical maneuvers.

The best way to manage iris prolapse is to avoid it. Begin in the preoperative area by giving atropine with the routine dilation drops. Although I avoid retrobulbar blocks in these patients, a lid block can help keep the patient comfortable and prevent posterior pressure from squeezing the lids. Reverse Trendelenburg positioning which pulls the diaphragm off the chest and helps prevent airway obstruction, also helps decrease posterior pressure.

A dose of intravitreal acetazolamide (Diamox; GlaxoSmithKline) may be given prior to starting the procedure. Although I rarely use mannitol, it is helpful to have it available if needed. I highly recommend the use of a viscoadaptive ophthalmic viscosurgical device (OVD), such as Healon V (Johnson & Johnson). Make paracenteses a little on the longer side to ensure they will be self-sealing. Irrigation is kept constant, and if I am about to come out of the eye, I have viscoelastic ready to fill.

In very short eyes (less than 18 mm), I take additional precautions prior to the first corneal incisions. A small conjunctival peritomy is opened in the temporal quadrant (I operate temporally), followed by a scleral cutdown to the suprachoroidal space at least 2 mm behind the limbus. If the sclera is overly thick or suprachoroidal fluid is encountered, a sizeable paracentesis is thinned to leave a scleral window of about 90% depth. In these eyes, I will start with bimanual incisions and create the capsulorhexis using a bent-needle cystitome and microforceps through the right-handed paracentesis before making the main wound.

In younger patients, when the nucleus is soft, it may be possible to remove the nucleus and cortex using a bimanual approach prior to making the main wound for IOL insertion. A primary posterior capsulotomy and limited core vitrectomy for aqueous misdirection may also be considered; in that case, a 3-piece IOL is placed in the sulcus with optic capture.

If you encounter intraoperative choroidal effusion or misdirection prior to removal of the crystalline lens, you should be prepared for a decompression procedure such as an iridozonulohyaloidectomy through the peripheral iris or a dry vitrectomy through the pars plana (which you have already prepared with your cut-down site).

MIGS Techniques in Short Eyes

All short eyes are on the angle-closure spectrum. In general, additional MIGS is not required because the relatively large crystalline lens is the main issue. Goniosynechiolysis can  easily be performed at the time of phacoemulsification. Goniotomy may be considered in more chronic cases that require multiple agents to control IOP preoperatively. There has been some literature on the role of endocyclophotocoagulation in plateau iris cases to help rotate the ciliary processes more posteriorly.

Conclusion

Successfully managing eyes at the extremes of axial length depends on anticipating anatomical challenges and adapting surgical techniques accordingly. Surgeons should carefully select IOLs, tailor fluidics, and choose MIGS procedures based on axial length–specific risks such as posterior iris bowing, zonular laxity, or anterior chamber crowding. Preoperative planning—including accurate biometry and consideration of viscoelastic use, positioning, and decompression strategies—can reduce intraoperative complications. Applying these targeted strategies allows for safer phacoemulsification and glaucoma interventions, helping surgeons achieve consistent outcomes even in eyes outside the typical axial length range. GP

Lauren S. Blieden, MD, is professor and vice chair of education at the Cullen Eye Institute, Baylor College of Medicine, in Houston. She is a consultant to Alcon, AbbVie, Elios, and New World Medical. Reach her at Lauren.Blieden@bcm.edu.