Cataract Surgery in Open-Angle Glaucoma

Introduction

Cataract and glaucoma often coexist in the eye and where they do the surgeon should develop a management plan which considers them both. Glaucoma is cataractogenic and cataract can increase intraocular pressure. Symptoms of cataract and glaucoma overlap – decreased contrast, increasing blur, poor night vision and glare occur due to both cataract and glaucoma. Cataract affects visual field results and may hinder disc observation and imaging. Cataract surgery may usefully lower intraocular pressure in the surgically naïve eye but when performed after glaucoma surgery often produces an increase in intraocular pressure. Cataract surgery is more technically challenging in patients with glaucoma and the postoperative management needs to be scrupulous with a close eye on IOP control ( Fig. 102-1 ).

Preoperative Assessment

The eye with glaucoma undergoing cataract surgery is at increased risk of complications. A formal preoperative assessment is recommended and should cover updated general medical issues, ocular examination findings, updated imaging and visual fields if required, biometry data, and explicit documented rationale for procedure.

Examination findings should include state of lids and lid margins, state of bleb/tube (if present), corneal health (which may include formal topography and endothelial imaging), gonioscopy findings, iris mobility and maximum pupil size, presence of PXF and its effects, dilated fundus exam and updated disc status (+/– imaging).

The stage of glaucoma needs to be re-addressed prior to surgery, and the possibility of worsening glaucoma for the patient's symptoms should be considered and evidence documented. In updating the glaucoma staging, the examiner needs to be aware that the presence of cataract can preclude an accurate assessment of the optic nerve, either by direct visualization or by imaging. Cataracts can alter the objective assessment of the optic nerve and retinal nerve fiber layer making subtle defects harder to identify. OCT can over-estimate RNFL loss with cataract, as retinal nerve fiber layer measurements on TD- and SD-OCT reduce with decreased signal strength (SS) due to cataract. Interestingly, PCO development has the same effect.

Cataract decreases visual field performance. Overall the visual field tends to show an increase in mean deviation and blunting of the pattern of standard deviation (PSD) with cataract, although PSD may be less affected using SITA algorithms. For example, extensions of focal defects, especially if they are quite sharply delineated, may be missed with increasing cataract ( Box 102-1 ).

The preoperative assessment should include whether it is better to have glaucoma surgery prior to cataract surgery or combined with cataract surgery, or is it likely to be needed in the postoperative period. Aqueous flare values tend to remain elevated for greater than one month, but generally fall by three months, following uncomplicated cataract surgery. Flare persists much longer where there are significant operative difficulties or diabetic retinopathy. Elevated flare may affect subsequent glaucoma surgery suggesting that, if intraocular pressure control is likely to be poor post-cataract and require surgery, then combined cataract and trabeculectomy may be a better option.

Preoperative biometry has become more accurate due to improved keratometry and non-contact laser axial length measurements. In spite of these advances, intraocular lens power calculation formulas can significantly mislead in the context of significantly shallow anterior chambers, unusual Ks, and the presence of silicone oil (which needs to be identified by the user) ( Fig. 102-2 ).

Anesthesia

Cataract surgery is increasingly done under topical anesthesia but this strategy may not be appropriate for the patient with glaucoma, particularly if the pupil is poorly dilating or the patient has other health problems. Sub-Tenon's anesthesia is a good alternative, particularly done in the inferotemporal quadrant. If retrobulbar anesthesia is chosen, care should be taken to minimize volume and potentially do without adrenaline/epinephrine in the anesthetic. Poor pupil dilatation should have been noted preoperatively, and maximal dilation achieved with timely and effective topical mydriatics.

Surgical Techniques

Cataract surgery in the glaucomatous eye may proceed in the same manner as normal, but will deviate where there is unusual ocular anatomy (trauma, buphthalmos, nanophthalmos, anterior segment dysgenesis, etc.), disorders of the cornea, poor pupil dilation or instability of the crystalline lens. In addition, prior glaucoma surgery will impact on wound site and globe behavior during surgery, and alter postoperative management.

Preoperation hypotony provides unique challenges to the surgeon. It is technically difficult to create satisfactory wounds and the antero-posterior stability of the crystalline lens can be poor due to slackening of the zonules. Furthermore, inflation of the anterior chamber with OVD often results in unusually posteriorly placed crystalline lens for surgery. Reinflating of the vitreous cavity with viscoelastic may be required to balance pressure across the lens/iris plane. This is usually achieved through the iridectomy.