How is the accuracy of biometry and visual acuity affected after glaucoma filtering surgery with phacoemulsification (Phaco - cataract removal using ultrasonic waves)?

Biometry Accuracy and Visual Outcomes After Combined Glaucoma Filtering Surgery with Phacoemulsification

Combined phacoemulsification with glaucoma drainage procedures achieves refractive outcomes within ±1.0D of target in approximately 71% of cases, with longer axial length being the primary risk factor for refractive prediction errors. 1

Biometry Accuracy

Overall Refractive Predictability

• Refractive outcomes within ±1.0D of target refraction are achieved in 71% of eyes at 3-6 months following combined phacoemulsification and glaucoma drainage device surgery 1
• The mean refractive prediction error (actual minus predicted spherical equivalent) is approximately -0.06D ± 0.75D in combined procedures 2
• This represents acceptable biometric accuracy, though slightly lower than standalone cataract surgery 1

Critical Risk Factors for Refractive Error

Longer axial length is the most significant predictor of refractive inaccuracy:

• Eyes with axial length >24.5mm demonstrate significant myopic shifts, with mean actual SE of -1.24D ± 0.79D versus predicted SE of -0.81D ± 0.76D (p=0.001) 2
• Eyes with postoperative SE outside ±1.0D from target had significantly longer mean axial length (25.37mm ± 0.98mm) compared to those within target (23.34mm ± 0.89mm, p=0.003) 1

Additional factors affecting biometric accuracy include:

• Preoperative visual acuity worse than 5/200 correlates with significant postoperative myopic shift (p=0.024) 2
• Preoperative foveal detachment increases risk of myopic shift (p=0.002) 2
• Surgically induced astigmatism of approximately 0.52D (range 0.02-1.49D) occurs in 29% of combined cases 1

Factors NOT Affecting Refractive Outcomes

• Age, central corneal thickness, preoperative anterior chamber depth, and pre/postoperative intraocular pressure do not significantly impact refractive outcomes 1
• Intraocular gas or air tamponade during surgery does not influence postoperative refractive error (p=0.336) 2

Visual Acuity Outcomes

Postoperative Visual Results

Visual rehabilitation is generally successful but varies by surgical technique:

• Combined phacoemulsification with trabeculectomy achieves IOP control <22mmHg in 97% of cases at 6 months 3
• Postoperative visual acuity is not significantly different between phacoemulsification-trabeculectomy and traditional extracapsular techniques 3
• Visual rehabilitation is faster with phacoemulsification-based combined procedures compared to extracapsular approaches 3

For combined phaco-goniosynechialysis procedures:

• 90.4% of eyes achieve IOP <20mmHg without medications 4
• Eight patients (approximately 17%) achieved 20/20 visual acuity 4
• No patients experienced worse visual acuity after surgery compared to preoperatively 4

Complications Affecting Visual Outcomes

Posterior capsule opacification:

• Significantly reduced incidence of early posterior capsule opacification with phacoemulsification-trabeculectomy compared to extracapsular techniques 3
• Fewer eyes require YAG laser capsulotomy with phacoemulsification approaches (p<0.001) 3

Clinical Recommendations

Preoperative Planning

• Exercise increased caution with biometry calculations in eyes with axial length >24.5mm, anticipating potential myopic shift 1, 2
• Consider adjusting IOL power selection toward more hyperopic targets in long eyes undergoing combined procedures 2
• Document preoperative visual acuity and foveal status, as poor baseline vision predicts greater refractive unpredictability 2

Surgical Technique Selection

• Phacoemulsification-based combined procedures offer faster visual rehabilitation without compromising IOP control compared to extracapsular approaches 3
• Combined procedures achieve IOP control rates of 85-97% at 6 months, comparable across different surgical techniques 3

Common Pitfalls to Avoid

• Do not assume standard biometry formulas will perform equally well in combined glaucoma-cataract surgery as in routine cataract surgery alone 1
• Anticipate approximately 0.5D of surgically induced astigmatism in nearly one-third of cases 1
• Recognize that while anatomic success rates are excellent (>90%), achieving precise refractive targets is more challenging than standalone cataract surgery 1, 3