Cataract Surgery in Post-Vitrectomized Eyes

1. Introduction

Pars plana vitrectomy is a surgical technique that allows a successful treatment of many diseases of the posterior segment of the eye, such as retinal detachment, proliferative diabetic retinopathy, vitreous hemorrhage, epiretinal membrane, or macular hole, among others. The increase in vitreoretinal surgery procedures has led to a predictable and consequent increase in cataract surgery in these eyes. Therefore, the ophthalmologist must be aware of the special characteristics of this type of patient and the impact of a vitrectomized eye on cataract surgery.

2. Development of cataract

Cataract formation or progression is one of the most frequent complications we can find after vitreoretinal surgery. According to several studies, up to 65–80% of the eyes develop a cataract in the 24 months following vitrectomy. [1, 2, 3, 4, 5, 6]

Although posterior subcapsular and cortical cataracts can be formed after surgery especially in young patients, nuclear cataracts are much more frequent. Transient subcapsular opacification in the early postoperative period is not unusual. The time interval between vitrectomy and phacoemulsification can vary between 9 and 29 months. [1, 2, 3, 7, 8, 9, 10, 11, 12]

Even though the exact etiology of cataracts formed after vitrectomy is not known, there are several elements that seem to have a role in it as predisposing or precipitating factors:

• Age: patients over 50 years of age show a significant increase in cataract incidence after retinal surgery when compared to younger ones. They usually develop a nuclear sclerosis, whereas posterior subcapsular opacification is more usual at earlier ages. Whenever there is a previous cataract, vitrectomy favors its progression. [1, 2, 8, 13, 14, 15]

• Composition of fluid infusion into the vitreous cavity: the high concentration of 150 mmHg of oxygen in the irrigating solutions used during vitrectomy, much higher than the 17 mmHg of the anterior vitreous or the 30 mmHg of the aqueous, may contribute to the oxidation of the proteins of the lens, thus accelerating the formation of cataracts. However, it remains to be demonstrated that this exposure to high levels of oxygen is maintained in the postoperative period. [2, 15, 16, 17]

• Diabetes: there seems to be a lower rate of cataract progression in vitrectomized diabetics (especially in cases of ischemic retinopathy) compared to patients without diabetes, given that the oxygen level in their vitreous is lower (Figure 1). [18, 19]

• Direct surgical damage: iatrogenic cataracts can be generated by direct trauma to the posterior lens capsule from the instruments used during pars plana vitrectomy, causing its rupture and producing a very rapid lens opacification. Trauma is more likely to be suffered in long difficult surgeries, such as retinal detachment with vitreoretinal proliferation. If a cataract is formed in the four months following retinal surgery, traumatic etiology should be suspected. [1, 20]

• Light toxicity: intense exposure to surgical microscope light or the fiber optic probe can be a factor that facilitates the oxidative damage of lens proteins. However, light sources currently incorporate Xenon light filter systems that eliminate the phototoxic fraction of the blue-ultraviolet wavelength, reducing the phototoxicity caused in the lens or in the retina. [2]

• Vitreous gel removal: the elimination of the vitreous seems to increase the level of retrolental oxygen, generating oxidation of the lens proteins. The incidence of cataracts is much higher after an extensive removal of the vitreous gel and it drops significantly when a limited vitrectomy or a nonvitrectomizing technique is performed. In other surgical procedures that do not include vitrectomy, such a scleral buckling or pneumatic retinopexy, the risk of inducing cataracts is also lower. [1, 2, 6, 17, 21, 22]

• Vitreous substitutes: the presence of gas bubble (SF6 or C3F8) or silicone oil in the vitreous chamber raise the incidence of lens opacification when compared with eyes without any tamponade after surgery. Long lasting substances increase even more the cataract progression. Lens opacity in patients with silicone oil is associated with epithelial cell metaplasia due to inhibition of lens metabolism (anaerobic glycolysis). Secondary gas-related lens opacities can appear as posterior subcapsular vacuoles, which sometimes can be transient and disappear if a layer of liquid is maintained between the gas bubble and the posterior surface of the lens. It is important for the patient to keep the head in a prone position, to prevent the meniscus of the gas bubble from contacting the posterior surface of the lens, and to avoid metabolic disruption of the lens cells. [1, 2, 8]

• Small gauge vitrectomy: although theoretically one of the advantages of the minimally invasive vitreo retinal surgery (23, 25 or 27 gauge) was the lower incidence of cataracts following the operation, there are no studies that demonstrate this relationship. No significant differences have been found between the different systems in the rate of cataract development. It seems that the progression of the lens opacification depends more on the amount of vitreous gel removed rather than the size of the instruments that are used. [1, 23, 24, 25]

3. Considerations before cataract surgery

The surgical criteria should be early, avoiding advanced cataracts requiring higher ultrasound power or poor posterior pole exploration. The final visual acuity after retinal surgery and the underlying retinal pathology for which vitrectomy was required to predict the visual prognosis of the patient should be identified through the anamnesis: retinal detachment with or without macular involvement, proliferative diabetic retinopathy with or without macular edema, history of ocular trauma or high myopia, among others. At times, it is difficult to determine whether the degree of visual impairment in the patient is due to underlying retinal pathology or to cataract progression. In patients operated on for macular disease who present metamorphopsia or central scotoma, these symptoms will persist after cataract surgery. Likewise, it is important to identify the time interval between vitrectomy and cataract, since when opacity occurs at intervals of less than 4 months, iatrogenic lens touch in the posterior capsule must be ruled out. [20]

In the ophthalmological examination, pupillary dilation should be evaluated, as in uveitic or diabetic eyes, and the state of the zonular fibers, since there may be phacoiridodonesis due to alteration of the zonule in vitrectomized eyes. It is important to perform a fundus examination to rule out retinal pathology and, occasionally, to perform an optical coherence tomography (OCT) to assess the status of the macula. In patients with macular edema, the need to treat it with an intravitreal injection before surgery or during the procedure itself will be assessed. In the case of not being able to visualize the fundus, an ocular ultrasound should be performed to assess the state of the retina and be able to rule out complications such as vitreous hemorrhage or retinal detachment that require combined surgery.

4. Intraocular lens calculation

Intraocular lens power calculation is based on the measurement of anatomical eye parameters. Regardless of the formula we apply, to calculate the intraocular lens (IOL) in our patients we must know precisely the axial length (AL), keratometry and anterior chamber depth (ACD). Prediction of IOL power in eyes undergoing retinal surgery can sometimes be challenging and certain considerations should be taken into account.

4.3 Axial length in oil-filled eyes

Phacoemulsification and silicone oil (SO) removal in a single act could avoid surgical risks and is optimal for patients with cataract formation in a short time after vitrectomy with SO tamponade. Obtaining accurate AL measurements in silicone oil-filled eyes can be difficult.

Whenever possible, we should quantify the AL in oil-filled eyes with optical biometers (optical interferometry or reflectance) because of the optical laser is not appreciably affected by SO, by its molecular weight or by the interfaces that remain between aqueous humor and silicone in eyes with incomplete filling. [35, 36] In the main menu of our optical biometer we will select the option “vitreous cavity filled with oil” and the refractive index of light will change from 1.33 in vitreous to 1.4 in silicone oil (Figure 2). [37]

However, cataracts generated by silicone oil are often dense and do not allow optical biometrics to be performed. It is estimated that in 4.7–17% of AL measurements, interferometry cannot be performed due to poor visual acuity, corneal opacity or dense cataract among others. [38, 39] Low coherence reflectometry and optical coherence tomography use longer wavelength than interferometry, so we can assume that the proportion of eyes measured with these techniques should be greater. [40] In cases where measurement with optical systems cannot be performed AL measurement becomes a biometric challenge.

The replacement of vitreous with silicone oil implies that the propagation of acoustic waves is modified. The speed of sound in a medium is inversely related to the refractive index of the medium. Because silicone has a higher rate than vitreous, it reduces the speed of sound a 36% approximately. The sound velocity declines from 1532 m/sec in the vitreous to 980 m/sec in 1000 centistokes molecular weight silicone oil. [41] This reduction in speed generates a higher axial length measurement. If we do not calibrate our ultrasonic biometer, we will generate a hypermetropic refractive defect.

If we use higher molecular weight silicone oil the speed variation would be different [42, 43, 44, 45].

If our ultrasonic biometer does not have a speed adjustment for eyes with silicone oil, we can multiply a corrective factor of 0.64 to the vitreous cavity length obtained with a speed of 1532 m/sec. [46] To calculate the axial length we will have to add the rest of the structures (anterior chamber depth, lens thickness and retrosilicone space) to the value obtained from vitreous cavity with the corrective factor. [37]

Another source of error appears when the vitreous cavity is not completely filled with SO. An aqueous space is generated between the oil and the retina, the “retrosilicone space”. It is maximum in supine position, decreases when the patient is erect and is minimized in the prone position. [47] And as we have seen before, it should be taken into account for IOL calculation. If we do not consider it, leads to a shorter and erroneous measurement of the AL in A-mode biometry.

Abu El Einen et al. [43] found better refractive results in oil-filled eyes explored by inmersion B-guided than in contact A-mode biometry. Although both are echographic techniques, immersion ultrasound prevents us from possible compression of the scanning probe on the cornea and mode B helps us to locate fovea, specially in patients with staphyloma or fluid interfaces. [48]

In addition to slower sound speed, SO absorbs sound, leading to poor penetration with low-quality echoes. [49] This significant sound attenuation generates poor identification of the retinal spike by contact A-mode biometry. [50] In these cases biometry may be unsatisfactory and other methods as we mention below have been proposed. Vitreoretinal surgeons should know that the appearance of cataract occurs after 3 months in 100% of the eyes with SO. [51, 52] Therefore, a useful strategy would be to perform a pre-vitrectomy biometry in all cases with macula on in which there is a possibility of fluid exchange by SO. [53] In these cases, we should take into account that the placement of a scleral buckle during surgery will also modify the axial length of the patient. [54, 55]

Another option is the two-step surgery with the removal of cataract and silicone oil in a first step and the placement of an implant in a second time if the retina remains stable. [56, 57]

El-Baha et al. perform more complex techniques with intraoperative biometry after remove SO with a sterilized ultrasonic biometer probe. [58] Elbendary et al. make an intraoperative calculation with a portable retinoscope. [59] These techniques consume more intraoperative time and require more specific devices that are not available in all centers, including a large stock of IOL powers.

5. Intraoperative complications

It has been reported that cataract extraction in eyes with previous vitrectomy is often more complicated because of various anatomic changes in the eye. In the vitrectomized eye, whose vitreous cavity was filled with air, gas or liquid solutions, the aqueous humor is the one that ends up occupying said space, so the lens does not have the counter pressure of the vitreous, which is a semi-solid and viscous substance, and during cataract surgery can occur significant variations in the depth of the anterior chamber that make the procedure difficult. Potential complications that may arise from this situation include bad pupil dilatation, zonule damage, posterior synechia, posterior capsule tears, increase mobility of complex lens-iris and altered intraocular fluid dynamics as a result of the absence of the anterior hyaloid face. Thus, cataract surgery (phacoemulsification) in vitrectomized eyes has been reported to be associated with an increased rate of complications. [74, 75, 76, 77]

Cataract surgery in the vitrectomized eye can be performed under topical anesthesia, or in complex cases local anesthesia. When surgery was performed under topical anesthesia, the anterior chamber was irrigated with lidocaine 0.5% before it was filled with an ophthalmic viscosurgical device. There are ophthalmologists who prefer peri- or retrobulbar anesthesia, since when the anterior chamber is deepened, oscillations of the irido-crystalline diaphragm occur with variation in pupillary diameter that generates discomfort to the patient. If the surgery is performed using local anesthesia (retrobulbar), it is necessary to be cautious with the pressure exerted by the Honan balloon. Excessive pressure exerted by this balloon could damage or increase damage to a compromised zonule, increasing the risk of intraoperative drop of the nucleus into the vitreous cavity. For this reason, the use of topical anesthesia is preferable for cataract surgery in previously vitrectomized eyes. Finally, general anesthesia will be reserved for children, neurological and psychiatric patients and bad collaborators.

Biro et al. reported posterior capsule tears and dropped nucleus in 7,3% in 41 vitrectomized patiens. [78]

Nevertheless, others authors suggest that eyes with and without prior pars plana vitrectomy (PPV) have a similar likelihood of having intraoperative complications. These authors reported that recognize the differences in the physiologic state of the vitrectomized eye compared with that of non-vitrectomized eyes reduced the frequency of intraoperative complications. [79]

A clear corneal incision for performing the phacoemulsification was recommended, avoiding the conjuntival-scleral scarring from previous retinal surgery. [80]

No intraoperative wound-related problems have been described using this clear corneal approach, with a 3-step wound construction with a 50% vertical groove.

In patients with inadequate dilation of the pupil, the use of intracamerular phenylephrine or the insertion of iris retractors or pupillary elongation maneuvers will be evaluated, and if there are posterior synechiae, synechiolysis will be performed with the help of viscoelastics.

In the case of severe crystalline opacities that do not allow the visualization of the background orange reflex, the use of trypan blue in the staining of the anterior capsule, facilitating capsulorhexis, will be considered. In vitrectomized eyes, trypan blue must be introduced into the anterior chamber slowly to avoid its diffusion to the vitreous chamber through zonular dehiscences. If this happens, phacoemulsification can be very complicated by the loss of the foveal reflex, increasing the risk of rupture of the posterior capsule.

If possible, very small capsulorhexis should be avoided to avoid capsular phimosis that later hinders the evaluation of the retinal periphery. Both cohesive viscoelastics that have expansive property allowing the management of mydriasis, and dispersives that protect the corneal endothelium can be used.

Phacoemulsification with a constant pressure minimizes complications in the event of significant ocular collapse. [81]

Fluctuations in the anterior chamber, such as the antero and retropulsion phenomenon, can be minimized by keeping the infusion bottle low, although sometimes there are unavoidable intraoperative mioses that make surgery difficult.

Accurately sized wounds, including the clear corneal incision for the phaco tip and the side port for the nucleus manipulator, help to maintain a relatively sealed chamber during surgery and minimize fluctuation of the anterior chamber depth.

In the case of having a reverse pupillary blockage, produced when the iris contacts the anterior capsule, preventing the flow from reaching the posterior chamber, it can be solved either by lifting the iris with a second instrument from the paracentesis or using the phaco tip lifting the iris and put the foot pedal in the irrigation level before any phaco manipulation.

In a study of 75 vitrectomized eyes, this blockage was observed in 53.3% of the cases during cataract surgery, especially in younger patients, with greater axial length and greater anterior chamber depth. [82]

Infusion deviation syndrome occurs when fluid migrates backward through the zonule and it increases the volume of the vitreous and causes flattening of the anterior chamber. Titiyal et al. [83] presented this complication in 12.3% of the 89 vitrectomized eyes during cataract surgery. To prevent this, it is recommended to carry out the hydration maneuvers carefully, reduce the flow of fluid within the anterior chamber (lowering the height of the bottles if possible or reducing the flow/aspiration rate). Once this complication appears, it is very useful to place in the pars plana a vitrectomy trocar without a valve to allow the pressure to escape from the posterior chamber and to be able to continue performing phacoemulsification.

Maneuvers that push the lens during phacoemulsification and cause zonular tension should be avoided. Thorough careful hydrodissection, confirmation of adequate lens rotation before phacoemulsification and gentle nucleus manipulation help to avoid unnecessary zonular damage and posterior capsule tears. If there is a fall of the nucleus or fragments to the vitreous cavity after the rupture of the posterior capsule, aggressive maneuvers should not be carried out when trying to recover them since they can generate ruptures in the retina and subsequent retinal detachment. The appropriate management in these cases is to perform a posterior approach to the complication through pars plana vitrectomy. In general, it is recommended to complete the vitrectomy if necessary, ensure by direct visualization that retinal tears have not been generated, removal of all fragments (either using the vitreotome or using the posterior chamber phacoemulsifier). In these cases, exploration of the peripheral retina to detect tears by indentation is highly recommended (Figures 3 and 4).

If there is good capsular support, a lens can be placed in the capsular bag remnants or in the sulcus if the anterior capsule remains intact. In the latter case, it is highly recommended to perform the Gimbel maneuver, which consists of dislocating the optic of the intraocular lens through the opening of the anterior capsule, keeping the haptics of the lens in sulcus. With this maneuver great stability in the implanted intraocular lens is obtained. The technique provides stability and long-term centration of the IOL and prevents vitreous from extending anterior to the IOL. [84]

If there is no capsular support, other alternatives must be chosen to place the intraocular lens, such as the sulcus-sutured lens or the iris fixation lenses.

The use of multifocal lenses in eyes with retinal pathology remains controversial, so it is generally preferred to implant single vision lenses.

6. Postoperative complications

Vitrectomized patients after cataract surgery have a higher risk of postoperative complications. In patients with previous macular surgery and diabetic eyes, a higher incidence of cystic macular edema has been observed. It was reported after a mean time of 42 days after cataract surgery. [85] Nevertheles, there are other studies which have not found CME however, OCT was not routinely used. Therefore, it is important to monitor these patients with fundus and OCT postoperatively since some are refractory cases and require subtenon or intravitreal treatment (Figure 5). [86, 87]

Patients with a history of retinal detachment or high myopia surgery may have a higher incidence of retinal detachment, so the peripheral retina should be evaluated throughout the postoperative period. The incidence of RD has been reported between 2% and 8% in different studies [88, 89, 90]. Cataract surgery in these patients can no have intra-operative complication which may predispose to RD. Therefore, this complication was a consequence of the previous posterior segment pathology in these eyes.

The incidence of posterior capsular opacification (PCO) was higher in vitrectomized eyes compared with nonvitrectomized eyes. [91, 92] It is ranging between 2.2% and 19.9% [15, 16, 17] within the first year after surgery. [88, 89, 90].

Finally, another complication in vitrectomized patients undergoing cataract surgery may be long-term subluxations or dislocations of the lens to the vitreous cavity. High myopia was the most frequent predisposing factor in 18.1% of the 83 eyes with this complication. [93]

In summary, cataract development and progression are known as frequent complications of PPV. Because of the application of vitreoretinal surgical techniques to a broader range of posterior segment diseases and because cataract surgery is frequently performed in postvitrectomy eyes, cataract surgeons should be familiar with the challenges of cataract extraction in vitrectomized eyes.