It is essential that the surgeon be able to recognize and identify patients with a higher risk of developing this surgical complication to take the appropriate measures and technique modifications to minimize the risk. In a good preoperative evaluation, most of these causes can be detected, including significantly hard cataracts, poor pupillary dilation, capsular pseudoexfoliation, previous trauma causing zonular weakness, and vitrectomized eyes lacking vitreous back support [2].

Dislocation of lens material during cataract surgery may be essentially due to two mechanisms: posterior capsule rupture (Fig. 1) and dehiscence of the zonules. Tearing of the posterior capsule can occur during the hydrodissection or when the nucleus is phacoemulsified. The latter is more frequent in eyes with variations in anterior chamber depth, especially if high levels of aspiration and power are used, and in previously vitrectomized patients, when the density of the vitreous does not exert posterior support for these changes. Capsular rupture can occur when the core is sculpted too close to the posterior capsule, especially when there is no good visibility. It can also be due to the shift from a dense area of the core to another softer area, where the increase in the suction force can drag nuclear, cortical, and capsular content quickly into the phacoemulsification handpiece opening.

When a posterior capsule tear is detected (Fig. 2), the phacoemulsification technique must be modified to prevent further tearing. The surgeon should avoid rotating the core as it may increase the defect and increase the risk of dislocation (Fig. 1).

Excessive handling and large fluctuations in chamber pressure should be avoided. The surgeon should use a second instrument to hold the nucleus and approach the phaco tip. If it is a large capsular rupture, it can be protected with a sheet slider, raising the upper pole of the nucleus while protecting underneath the aperture and helping extraction by phacoemulsification. Finally, it can be converted to extracapsular extraction of the core with large corneal incision [3].

Lens fragment dislocation is a potentially serious ocular complication with clinical manifestations largely dependent on the amount of dislocated material. While smaller fragments may be generally well tolerated, large amounts can cause severe intraocular inflammation. The intensity of this inflammation as well as the final visual prognosis will depend on the type of lens material, with nuclear fragments causing far more severe symptoms than remnants of epinucleus or cortex. [4].

The most common complications include decreased visual acuity, intraocular inflammation, corneal edema, and ocular hypertension. Less frequent complications are retinal detachment, choroidal detachment, vitreous hemorrhage, cystoid macular edema, and endophthalmitis.

A decrease in vision is the most common symptom of this complication with several series reporting visual acuity rates of 20/400 or worse from 41.2 to 89 % [5–7]. Intraocular inflammation is present in most cases with reported rates between 67.1 and 87 % [5–7] and often manifests as corneal edema, secondary glaucoma, or cystoid macular edema. Also known as phacoanaphylactic uveitis, this inflammation is caused by proteins of the lens fragments and may manifest as conjunctival hyperemia with ciliary injection, eye pain, and ocular hypertension. In some cases, this inflammation can be very severe with cell/flare >2+ accompanied by a hypopyon, giving the appearance of a real endophthalmitis. Cases of acute endophthalmitis have been reported that are associated with dislocation of lens fragments and have been demonstrated by positive cultures [8]. Therefore, in cases with the presence of severe intraocular inflammation, culture is required to rule out infection and pursue appropriate treatment.

Corneal edema is another manifestation of lens fragment dislocation and has been estimated as having an incidence of 46–61 % [5, 6]. Corneal edema may be caused by intraocular inflammation as well as by increased intraocular pressure and should be treated rapidly as vitrectomy should ideally be performed with greatest possible corneal transparency.

An increase in intraocular pressure as high as 25–30 mmHg can be seen in about half of these patients [6, 7]. The increase in pressure may be due to either the massive presence of inflammatory cells at the level of trabecula or the remains of lens material. This acute increase in intraocular pressure can cause chronic glaucoma if the inflammation remains persistent.

Retinal detachment is present with an incidence that varies between 3.6 and 21.5 % [1, 9]. It is a feared complication and can be responsible for poor visual prognosis for some patients. This detachment is usually caused by surgical maneuvers in complicated cataract surgery or during subsequent vitrectomy which can cause retinal tears or secondary vitreous traction. Excessive irrigation and the search for material in the vitreous cavity increase the risk of retinal breaks. The lens fragments themselves may directly cause retinal breaks as well as indirectly lead to vitreoretinal traction and neurosensory detachment secondary to inflammation, bleeding, and subsequent cellular proliferation [10].

Cystoid macular edema can appear as a late complication secondary to intraocular inflammation caused by the lens material in approximately 7 % of cases [6].

Detailed patient evaluation is important before considering vitrectomy to obtain the best possible results. This preoperative evaluation will depend on the time lag between initial surgery and vitrectomy. If the vitrectomy is immediately following surgical complication, the evaluation will be shallower; however, if a vitreoretinal surgeon or necessary equipment is not available, it is more convenient to delay the surgery and undertake a thorough patient evaluation.

Knowledge of the patient’s ocular history helps to determine whether preexisting disease may have caused the complication and determine viability of subsequent surgeries. Eye trauma, high myopia, previous episodes of uveitis, diabetic retinopathy, vitrectomy, sclerectomies, or previous valve implants may complicate surgical removal of fragments or help determine the surgical approach.

When examining the patient, the first thing to be noted is the visual acuity. This will depend on many factors such as the presence of fragments in the visual axis, macular edema, the degree of cellularity in the anterior chamber, and vitritis. Visual acuity is an important prognostic factor because visual acuity of 20/40 or better has been shown to be an indicator of better final visual acuity [9]. The external examination should be performed after and the degree of eye and eyelid inflammation assessed.

Pars plana vitrectomy for removal of retained lens fragments should be indicated when the displacement of the lens to vitreous cavity occurs spontaneously, secondary to trauma, or following a surgical complication [11–16]. It is also considered when a large part of the crystalline remains have gone into the vitreous cavity and/or persisted in the capsular bag.

Surgery must also be considered to prevent complications attributable to the retention of fragments in the vitreous whether these appear immediately (ocular hypertension, inflammatory reaction), late (cystoid macular edema, retinal detachment), or may affect the visual acuity as in the case of vitreous opacities or symptomatic floaters.

The indication for vitrectomy is not so clear if lens residues are scarce and do not generate pressure or inflammation beyond the early postoperative period [14, 17]^. In fact, if the material amount is small, it may gradually be reabsorbed, thus avoiding further surgery.

There is some controversy about determining the optimal timing of vitrectomy to remove the lens fragments. Currently, there are two trends: either to perform the vitrectomy as soon as possible after cataract surgery (early surgery) [18, 19] or do it in a deferred way [9, 15, 16, 20].

Early vitrectomy, immediately after cataract surgery, involves only moderate technical difficulty. In addition, the condition is prevented from worsening and a second procedure is avoided. Wilkinson suggests that the absence of macrophages and other inflammatory markers during the first days after cataract surgery leads us to think that early surgery may prevent further complications [11].

Corneal opacity appears often on the day after surgery and limits the visualization, making it necessary to delay the surgery until the eye is in good condition.

On the other hand, performing vitrectomy when the complication arises makes it necessary to have a vitreoretinal surgeon available with assistants familiar with the technique. In addition, due to the widespread use of topical anesthesia for cataract surgery, either additional peribulbar or retrobulbar anesthesia is required.

Vitrectomy, when deferred, can be performed with the necessary equipment. In addition, the resolution of corneal edema provides transparent media. Moreover, greater hydration of cortex and core debris that occurs over time increases the ease of fragment extraction.

The disadvantages of delaying vitrectomy include delayed resolution of the issue, the need for a second operation, and the increased possibility of a secondary pathology (chronic glaucoma).

Several studies conclude that the time lag before vitrectomy does not significantly influence the final functional outcome [9, 14, 15, 20–22].

However, these findings may be biased by the limited number of cases in the series and the consequent variability.

Although there are studies like those of Kageyama et al. showing that 82 % of patients undergoing vitrectomy at the time of complicated cataract surgery reach a BCVA of 20/40 or greater [12], the literature does not support early vitrectomy as a superior choice.

An initial aggressive drug treatment can aid in delayed vitrectomy by improving corneal edema and acute inflammation, thereby improving visualization and conditions to perform the surgery.

Moreover, other studies conclude that the risk of secondary open-angle glaucoma increases when surgery is delayed by over 1 week [9, 15, 21].

Since it is not always possible to perform vitrectomy the same day as cataract surgery, the most appropriate time to carry it out will depend on the degree of corneal transparency and intraocular inflammation, the patient’s general condition, and the availability of instruments and skilled staff.

In general terms, assuming there are no significant complications requiring earlier surgery, the vitrectomy should be performed in the week following failed phacoemulsification [2].

Evaluation depends on when the vitrectomy for extraction of lens remnants is performed. Theoretically, although there is no consensus, this second surgery should ideally occur at the same time as the surgical complication, even though this means a very superficial examination of the patient is undertaken. In this case the surgeon must take into account the intraocular pressure of the eye—usually hypotonus—especially if previously the eye has been manipulated by the cataract surgeon in an attempt to remove the vitreous core. Hypotonia may hinder the incision maneuvers through trocars, which may only incompletely perforate the wall of the globe, causing subretinal fluid infusion. To avoid this, the eye should be filled with viscoelastic fluid through the anterior chamber or a saline infusion through the paracentesis (Figs. 3 and 4).

Because immediate action is not the most frequent due to the difficulty of having a vitreoretinal surgeon available, deferred action is often necessary. In that case a complete clinical record and exploration can be made.

Slit-lamp examination assesses the degree of corneal transparency when special emphasis is placed on the endothelium and helps determine the choice of location of lens implantation in cases of aphakia. Incisions and degree of cooptation, presence of vitreous incarceration, and remains of suture are problems which also must be solved to avoid further complications. Also important is the evaluation of the cellularity in anterior chamber (Tyndall phenomenon) that can range from slight to a true hypopyon and the presence of blood or fibrin and lens fragments that may be housed in the anterior chamber, trabecular angle, or behind the iris. As discussed above, in cases of suspected endophthalmitis, obtaining microbiological cultures and treatment will be a priority. Both corneal edema and inflammation should be treated but preferably without delaying the removal of lens material. Also pupillary dilation will need to be evaluated because poor mydriasis due to the presence of synechiae complicates the surgery and requires maneuvers to increase the pupil size. Evaluating the structure of the remaining posterior capsule in aphakic cases helps to determine the necessity of implanting the lens either in capsular bag, in sulcus, or sutured. In cases where the lens is implanted, the surgeon should assess the stability of the lens, correct its position if necessary to prevent posterior dislocation, or in cases of instability remove it along with the crystalline remains and defer implantation of an intraocular lens to a later date.

The measurement of intraocular pressure and its pharmacological control in cases of elevation are essential before performing the vitrectomy. Also, the presence of hypotonia can suggest a major complication such as retinal detachment.

Once the anterior segment is evaluated, a thorough dilated fundus exam should be performed to explore the posterior segment. Through indirect ophthalmoscopy, we can determine the degree of transparency of the vitreous, the presence of bleeding, and size, density, and amount of dislocated lens material. Nuclear fragments cause more inflammation and have a worse prognosis than the remnants of cortex or epinucleus, making composition more important than size. The presence of vitreous hemorrhage is a sign of severity that can be related to inadequate manipulation, direct trauma, or vitreoretinal traction. If the low intensity of media opacity permits indirect ophthalmoscopy, the surgeon must always rule out the presence of retinal breaks that can be treated preemptively with argon laser and the presence of choroidal detachments, most of which can be resolved with conservative treatment. Retinal detachment requires urgent vitrectomy as inflammation caused by the lens fragments in the vitreous cavity increases the risk of developing a proliferative vitreoretinopathy [23]. Finally, the presence of cystic macular edema or Irvine-Gass syndrome, which require early treatment, must be excluded.

Although pars plana vitrectomy itself resolves most symptoms and complications of retained lens fragments, some risks remains. This risk of retinal detachment has been reported in several series ranging from 4 to 10.3 % [24–27].

Moore et al. found an incidence of retinal detachment of 7.3 % before vitrectomy to remove lens fragments and 5.5 % after, with 42 % of these detachments occurring 3 months after surgery and half of them occurring with macular involvement [28]. Due to this, some surgeons recommend performing prophylactic retinal photocoagulation 360° to reduce the risk of subsequent retinal breaks [29].