What are the typical changes in visual acuity, refraction (spherical equivalent, astigmatism), axial length, anterior chamber depth (ACD), and central macular thickness (CMT) before and after cataract surgery?

Pre and Post-Cataract Surgery Changes in Ocular Parameters

Cataract surgery typically results in significant changes in visual acuity, anterior chamber depth, refraction, and occasionally central macular thickness, with anterior chamber depth deepening by approximately 1.3-1.9 mm postoperatively depending on preoperative anatomy.

Visual Acuity Changes

• Significant improvement in uncorrected visual acuity (UCVA) and best-corrected visual acuity (BCVA) is the primary outcome of successful cataract surgery 1
• The degree of improvement depends on:
  • Accuracy of intraocular lens (IOL) power calculation
  • Management of pre-existing astigmatism
  • Type of IOL implanted (spherical vs. aspheric)

Refractive Changes

Spherical Equivalent

• Postoperative refractive outcomes are influenced by preoperative anterior chamber depth (ACD) and axial length (AL) 2
• A hyperopic shift (approximately +0.57 ± 0.47 D) occurs when ACD change is less than 1.65 mm 2
• A myopic shift (approximately -0.18 ± 0.62 D) occurs when ACD change is greater than 1.65 mm 2
• With modern IOL calculation formulas and techniques, 67-93% of eyes can achieve within ±0.5 D of target refraction 1

Astigmatism

• Pre-existing astigmatism can be reduced through surgical techniques:
  • Opposite clear corneal incisions (OCCIs) can reduce pre-existing astigmatism by approximately 1.3 D (±0.9 D) 3
  • Single clear corneal incision typically induces or reduces astigmatism by about 0.4 D 3
• Residual astigmatism affects UCVA differently depending on IOL type:
  • With spherical IOLs, UCVA correlates significantly with residual astigmatism 4
  • With aspheric IOLs, UCVA is less affected by residual astigmatism up to 1.5 D 4

Anatomical Changes

Anterior Chamber Depth (ACD)

• ACD typically deepens after cataract surgery and stabilizes after approximately 2 weeks 2
• The magnitude of ACD change depends on preoperative factors:
  • Shallow preoperative ACD results in larger postoperative change (1.92 ± 0.40 mm) 2
  • Deep preoperative ACD results in smaller postoperative change (1.33 ± 0.42 mm) 2
  • Short axial length eyes show greater ACD change (2.12 ± 0.37 mm) compared to long axial length eyes (1.32 ± 0.49 mm) 2
• Postoperative ACD can be predicted using regression formulas:
  • Postoperative ACD = 3.524 + 0.294 × preoperative ACD 2
  • Postoperative ACD = 3.361 + 0.228 × (preoperative ACD + 1/2 lens thickness) 2

Axial Length (AL)

• Axial length typically remains stable after cataract surgery
• Preoperative AL significantly influences postoperative ACD and refractive outcomes 2, 5
• Short eyes (<22.20 mm) are more prone to hyperopic outcomes and require careful IOL selection 1

Central Macular Thickness (CMT)

• While not specifically addressed in the provided evidence, transient increases in CMT can occur postoperatively due to inflammatory response
• This typically resolves within weeks to months after surgery

Clinical Implications and Pitfalls

1. Preoperative Measurements:

   • Accurate measurement of preoperative ACD and AL is crucial for IOL power calculation 5
   • Multiple variables (AL, preoperative ACD, keratometry, lens thickness, refraction) should be considered for predicting postoperative ACD 5

2. IOL Selection:

   • For eyes with significant pre-existing astigmatism, consider surgical techniques like OCCIs or toric IOLs 3
   • Aspheric IOLs may provide better UCVA in cases with residual astigmatism >1.5 D 4

3. Refractive Surprises:

   • Be aware of potential hyperopic shift in eyes with shallow ACD and short AL 2
   • Consider adjustable IOL technologies for high-risk patients (e.g., axial hyperopes) to address postoperative refractive errors 1

4. Formula Selection:

   • Choose appropriate IOL calculation formula based on AL:
     • Hoffer Q for AL < 22.0 mm
     • SRK/T for 22.0 mm ≤ AL ≤ 30.0 mm
     • Haigis for AL > 30.0 mm 2

By understanding these typical changes and their relationships, surgeons can better predict outcomes, select appropriate IOLs, and manage patient expectations for cataract surgery.