Cataract surgery in an eye which has undergone a prior pars plana vitrectomy is different in many ways, including lens power calculation, intra-operative techniques, and even post-operative management.
Pars plana vitrectomy, particularly with smaller gauge instrumentation, is a safe and effective surgery that is essential in the treatment of a variety of posterior segment pathologies including retinal detachments, diabetic retinopathy, and macular lesions. But performing a vitrectomy, particularly with the use of intra-ocular gas or silicone oil, can induce cataracts, even in younger patients.
Cataract surgery in an eye which has had a prior vitrectomy can be challenging because the absence of the vitreous can lead to anatomic alterations, such as an overly deep anterior chamber and less support of the crystalline lens. Successful cataract surgery in these patients is important to restore their vision as well as to give the vitreo-retinal specialists a clear view to monitor the posterior segment in the future.
Pre-Operative Evaluation
The patient’s history is particularly important to determine the onset of symptoms and the development of the cataract. After most pars plana vitrectomies, cataracts develop slowly, over the course of months or years after the retinal surgery, in the form of increased nuclear sclerosis and often posterior subcapsular opacities. The use of intra-ocular gas as a retinal tamponade may induce cataract changes at a somewhat more rapid rate, but still it is typically months before the patient notices a visual decline.
If the patient reports a history of quickly developing a cataract, such as a white cataract, days or weeks after the vitrectomy, then iatrogenic damage to the lens capsule should be suspected. While it is uncommon, it is possible for the pars plana vitrectomy instruments to damage the posterior lens capsule, which can rupture and then cause the lens to opacify very quickly.
Clinical examination should include careful evaluation of the posterior capsule either by slit-lamp or ultrasound, if direct visualization is not possible. If the ultrasound shows an abnormally large lens thickness or an out-pouching of the posterior lens surface, a defect in the posterior lens capsule likely exists. You should proceed with extreme caution because the lens nucleus can easily fall into the vitreous cavity as the posterior capsule defect expands from the infusion pressure of the phaco probe. Perhaps a pars plana lensectomy would be the best approach followed by placement of a sulcus IOL.
Intra-ocular lens (IOL) calculations may be somewhat less accurate due to difficulty in estimating the post-operative effective lens position. The absence of vitreous and possible prior damage to zonular structures may cause the IOL to sit more posterior than predicted, resulting in a hyperopic surprise. This is why aiming for a mild degree of post-operative myopia by using a slightly higher-powered IOL tends to give better results.
The effective lens position of the IOL will likely be more posterior and therefore a slightly higher IOL power should be chosen to achieve the desired refraction.
If the eye is otherwise normal with respect to the capsule and zonular structures, a single-piece acrylic IOL is my first choice. A three-piece monofocal acrylic IOLs may help in eyes where zonular integrity is in question since there are more options for lens fixation. The three-piece IOL can be placed in-the-bag, in-the-sulcus, or sulcus placement of the haptics with optic capture through the capsulorhexis. In addition, the acrylic material minimizes condensation on the optic and adhesion to silicone oil if a repeat vitrectomy is needed in the future.
Intra-Operative Techniques
The vitreous in a virgin eye is semi-solid, thick, and viscous which allows it to help support the cataract during surgery when the patient is supine. This results in a normal anterior chamber depth and a more routine cataract surgery. In an eye which has undergone a prior vitrectomy, saline and aqueous have replaced the vitreous resulting in a fluid filled eye which does not provide additional support of the cataract during phacoemulsification. This causes the anterior chamber tends to be overly deep during cataract surgery. To address this, the infusion pressure can be decreased by lowering the bottle height on the phacoemulsification machine. To compensate for lowered infusion, the aspiration flow rate should also be dropped. Also, preventing reverse pupillary block is an important consideration in this situation
In some cases, posterior support can be increased by giving a retro-bulbar block since the anesthetic bolus will tend to provide pressure to the back of the eye. If there is reverse pupillary block, caused when the iris makes a tight seal on the anterior lens capsule, this can be solved by tenting up the iris with a second instrument or even by placing a single iris hook. These eyes may also have zonular damage or laxity which can lead to difficulties during cataract surgery. If there is a posterior capsule rupture, either from the vitrectomy or cataract surgery, the lens nucleus should be brought forwards, out of the capsular bag and viscoelastic placed behind it to support it. If any cataract pieces are displaced into the posterior segment, they will rapidly descend onto the retina due to the lack of vitreous. These pieces are best removed by the vitreo-retinal surgeon using a pars plana approach.
In some cases there may be pigment such as from the RPE adherent to the back surface of the posterior lens capsule. This will not be possible to easily remove during cataract surgery, but it can be easily treated with the YAG laser in the near future after the IOL is secured by capsular contraction.
Post-Operative Management
The patients who undergo cataract surgery after a prior retinal surgery are at higher risk for some post-operative complications. Patients with prior macular surgery are more prone to cystoid macular edema, even after a beautifully performed cataract surgery. These patients should be treated with anti-inflammatory medications for a prolonged period and their macular status should be monitored at post-op visits. Patients with prior retinal detachment surgery are at a higher risk for a recurrent detachment after cataract surgery, so their retinal periphery should be checked carefully. In addition, it may take longer for these patients to heal after surgery and to achieve a stable post-operative refraction.
Patients who undergo a pars plana vitrectomy are more likely to develop a cataract, typically months to years after their initial retinal surgery. With carefully pre-operative evaluation, select intra-operative techniques, and close post-operative monitoring these patients can achieve excellent results from their cataract surgery and restoration of their vision.
Click below to watch cataract surgery in an eye with prior pars plana vitrectomy:
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Very much informative sir..