Cataract and glaucoma are the first and second leading causes of blindness worldwide.^{1, 2} Although usually not severe enough to cause blindness, it is not surprising that these two diseases occur simultaneously in many patients. Many studies have demonstrated intraocular pressure reduction after cataract surgery.³ However, most recent data indicates that IOP reduction after cataract surgery is more significant and sustained than previously thought.⁴

The mainstay of glaucoma treatment is to lower intraocular pressure. Traditional glaucoma surgeries such a trabeculectomy and tube shunts work well to lower intraocular pressure and decrease progression of glaucoma, but these procedures carry significant risk.^{5, 6} Many patients with glaucoma have concurrent cataracts and some studies have suggested that glaucoma itself is a risk factor for cataract development.⁷?⁹ Glaucoma filtering procedures, peripheral iridotomy and some glaucoma medications increase the risk of cataract formation.^{5, 10}?¹⁷ Historically, patients with moderate to advanced glaucoma with concurrent cataracts would have either a combined procedure or a two-stage surgery.^{6, 18}?²² Surgeons have traditionally felt that cataract surgery lowers IOP in open angle glaucoma (OAG) only slightly and temporarily - despite a paucity of robust data.²³ In contrast, current data demonstrates a greater and more sustained IOP reduction.^{4, 10} As such, cataract surgery may be a safe alternative to glaucoma surgery in some patients and could shift the surgeon's approach in treatment of concurrent cataract and glaucoma.

The earliest studies of intraocular pressure after cataract surgery showed little if any reduction of intraocular pressure.²⁴?²⁶ However, these results probably don't apply today because of advances in surgical technique and intraocular lens technology. As extra capsular surgery became the standard, studies began to demonstrate a lowering of IOP²⁷ sometimes on a sustained basis.¹⁰ The conventional wisdom that cataract surgery lowers IOP by two to four? mmHg for a couple years was partially confirmed by the only meta-analysis of the topic.²³ This meta-analysis showed a long term mean IOP reduction of two to four? mmHg. However, long term was defined as longer than 24-hour follow-up (although many studies had even longer follow-up). Additionally, data in nearly all of the studies showed only mean IOP change and did not stratify patients based on preoperative IOP which has critical significance when interpreting the data. Studies which did stratify patients based on preoperative IOP clearly demonstrated that patients with higher preoperative IOP enjoy the greatest reduction of IOP after cataract surgery.^{4, 28, 29} Longer term studies have shown a drop in IOP of about three mmHG in POAG patients and nonglaucoma patients with 75-85% of patients maintaining a IOP reduction at five years.³⁰?³⁴ IOP can be controlled in 20% of patients with OAG without drops following cataract surgery.³⁵

The method of cataract extraction may influence the reduction of IOP. Phaco emulsification (particularly clear cornea phaco emulsification) seems to lower IOP more than manual extra capsular cataract extraction.^{10, 27, 36, 37} The type of OAG may also influence IOP reduction. Pseudo exfoliation patients may have an even greater long term decrease in IOP than POAG patients even though IOP often rises on postoperative day one.³⁸?⁴⁰ However, early IOP variability following cataract surgery has not been associated with clinical consequence.⁴¹ Many other factors such as pressurization at the time of surgery, immediate postoperative medications, and visco elastic type contribute to short term IOP fluctuations following surgery.⁴²?⁴⁴

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Conflict of Interest: None declared.