Does cataract surgery affect intraocular pressure (IOP) in patients?

Does Cataract Surgery Affect Intraocular Pressure?

Yes, cataract surgery consistently reduces intraocular pressure (IOP) in most patients, with an average reduction of approximately 2 mmHg, and this effect is particularly pronounced in patients with pre-existing glaucoma or elevated baseline IOP. 1, 2, 3

Magnitude of IOP Reduction

General Population

• Cataract surgery with IOL implantation alone results in a modest IOP reduction of less than 2 mmHg on average in patients without glaucoma 1
• In real-world settings, mean IOP decreases from approximately 15.2 mmHg preoperatively to 14.2 mmHg at 12 months postoperatively 2

Glaucoma Patients

• Patients with primary open-angle glaucoma (POAG) experience greater IOP reduction after cataract surgery compared to non-glaucomatous patients 2, 3
• In early POAG, cataract surgery reduces mean IOP by 2.22 mmHg, with 34% of eyes achieving at least 3 mmHg reduction 3
• Normal-tension glaucoma patients show significant IOP reduction (from 14.7 mmHg to 11.4 mmHg) along with decreased IOP fluctuations over 24 hours 4

Patients with Elevated Baseline IOP

• Higher preoperative IOP predicts larger postoperative IOP reduction 2, 3
• Eyes with preoperative IOP ≥21 mmHg show mean postoperative IOP reduction ranging from -6.2 to -6.9 mmHg 2
• Eyes with preoperative IOP ≥24 mmHg experience mean IOP reduction of 4.03 mmHg, with 81% achieving at least 3 mmHg reduction 3

Angle-Closure Disease

• Patients with primary angle closure (PAC) with elevated IOP and primary angle-closure glaucoma (PACG) achieve superior IOP control with clear lens extraction compared to laser peripheral iridotomy (LPI) 1
• The EAGLE Study demonstrated that clear lens extraction provides greater IOP control and quality of life benefit for PAC and PACG patients compared to standard LPI 1
• Lens extraction significantly widens the anterior chamber angle in eyes with primary angle-closure disease 1

Predictors of IOP Reduction

Anatomical Factors

• Increased lens thickness is the anterior segment parameter most strongly associated with IOP changes after cataract surgery in glaucoma patients 5
• Increased axial length is also associated with greater IOP reduction 5
• Anterior chamber depth alone is not predictive of IOP reduction 3

Medication Factors

• Patients on fewer preoperative glaucoma medications experience larger IOP reductions after cataract surgery 3
• An average IOP decrease of 16.5% was observed among patients in the Ocular Hypertension Treatment Study after cataract extraction, persisting for 3 years postoperatively 1

Early Postoperative IOP Spikes

Incidence in Normal-Tension Glaucoma

• IOP spikes occur in less than 3-5% of normal-tension glaucoma patients after cataract surgery, similar to non-glaucomatous controls 6
• Both normal-tension glaucoma and control groups show gradual IOP decrease in the early postoperative period with no significant difference between groups 6

Risk Factors for IOP Spikes

• IOP spikes on postoperative day 1 occur in 45.8% of glaucoma patients when defined as IOP ≥21 mmHg with ≥5 mmHg increase, and in 29.2% when defined as ≥10 mmHg increase 5
• Increased lens thickness and lower number of preoperative medications are significant predictors of postoperative IOP spikes 5
• Mean postoperative day 1 IOP (22.8 mmHg) is significantly higher than mean preoperative IOP (15.3 mmHg) in glaucoma patients 5

Clinical Implications for Combined Surgery

When to Consider Combined Cataract-Glaucoma Surgery

• If IOP is well-controlled on one or two medications, cataract surgery alone may be adequate with the additional benefit of modest IOP lowering 1
• If IOP is markedly uncontrolled on several medications after laser trabeculoplasty and the patient has moderate cataract, glaucoma surgery should be performed first, followed by cataract surgery once IOP is controlled 1
• Generally, combined cataract and glaucoma surgery is not as effective as glaucoma surgery alone in lowering IOP 1

Surgical Considerations

• Use of mitomycin C (MMC), but not 5-fluorouracil, results in lower IOP in combined procedures 1
• Patients with mild cataract requiring filtration surgery may be better served by filtration surgery alone followed by later cataract surgery 1
• Combined procedures offer protection against IOP rise that may complicate cataract surgery alone and eliminate risk of bleb failure with subsequent cataract surgery 1

Special Considerations

Femtosecond Laser-Assisted Cataract Surgery

• During femtosecond laser-assisted cataract surgery, IOP briefly increases upon application of the suction ring and vacuum 1
• This effect may cause additional damage in patients with advanced optic nerve damage 1
• These procedures may be relatively contraindicated in patients with advanced glaucomatous damage, especially after trabeculectomy 1

Postoperative Monitoring

• Establish preoperative and baseline documentation of optic nerve head status and visual field to facilitate subsequent glaucoma management 1
• Monitor for corticosteroid-induced IOP elevation in the postoperative period, which can be masked by interface fluid accumulation in certain circumstances 1