Anterior Chamber Depth and Axial Length Changes After Phacoemulsification
Phacoemulsification consistently increases anterior chamber depth (ACD) by approximately 0.86-1.43 mm depending on the measurement reference point, with these changes stabilizing by 1 month postoperatively and persisting long-term, while axial length itself does not change as it represents the total eye length from cornea to retina.
Anterior Chamber Depth Changes
Magnitude and Timeline of ACD Increase
The anterior chamber deepens significantly after phacoemulsification, with the extent depending on the anatomical reference point used for measurement 1:
- Angle-referenced ACD (ACD1): Increases by approximately 0.1 mm (from 3.06 mm to 3.16 mm) 1
- Pupil-referenced ACD (ACD2): Increases by approximately 0.86-0.87 mm (from 2.76 mm to 3.62-3.63 mm) 1
- Lens-referenced ACD (ACD3): Shows the most dramatic increase of 1.37-1.43 mm (from 2.54 mm to 3.91-3.97 mm) 1
These changes are evident as early as 1 week postoperatively and remain stable through 1 month and beyond 1. The 90-day follow-up data confirms persistent ACD deepening with statistically significant increases maintained at 3 months 2.
Factors Influencing ACD Changes
Baseline axial length significantly predicts the magnitude of ACD change 3:
- Eyes with shorter axial lengths (21.0 to <23.0 mm) show greater relative ACD increases 3
- Eyes with longer axial lengths (≥27.0 mm) demonstrate different patterns of change 3
- Preoperative ACD differs significantly between axial length groups, with greater increases observed as axial length increases 3
Capsulorhexis size affects final ACD positioning 2:
- A 4 mm capsulorhexis results in deeper postoperative ACD (3.73 ± 0.32 mm) compared to 6 mm capsulorhexis (3.50 ± 0.33 mm) at 90 days 2
- The ACD/axial length ratio is significantly higher with smaller capsulorhexis (0.152 vs 0.142) 2
Axial Length Considerations
Axial length does not change after phacoemulsification because it represents the fixed anatomical distance from the corneal surface to the retinal pigment epithelium 3. However, axial length serves as an important predictor of postoperative changes in other parameters 3.
The relationship between preoperative axial length and postoperative outcomes includes 3:
- Shorter eyes (AL <23.0 mm) experience statistically significant IOP decreases postoperatively 3
- Longer eyes (AL ≥25.0 mm) may experience IOP increases in the early postoperative period 3
Associated Angle Changes
The iridocorneal angle widens significantly after phacoemulsification, with more pronounced effects in eyes with narrow preoperative angles 4:
- Angle opening distance at 500 μm (AOD500) increases from 0.179 mm to 0.389 mm in narrow angle eyes at 6 months 4
- Both nasal and temporal iridocorneal angles show statistically significant widening at 1 week and 1 month postoperatively 1
- AOD500 increases significantly from 0.440 mm preoperatively to 0.522 mm at 3 months in open angle eyes 5
Clinical Implications
Preoperative anterior chamber parameters predict postoperative IOP changes 5:
- Higher preoperative lens vault correlates strongly with greater IOP reduction (r = 0.606) 5
- Smaller preoperative AOD and TISA values predict greater IOP reduction 5
- Mean IOP reduction of 2.43 mmHg occurs by 3 months in non-glaucomatous eyes 5
Common Pitfalls
The crystalline lens rise measurement (mean 0.497 mm) and pseudophakic posterior chamber depth (mean 0.322 mm) demonstrate the anatomical repositioning that occurs with IOL placement 1. These measurements help explain why the lens-referenced ACD shows the most dramatic change—the IOL sits more posteriorly than the anterior lens capsule position but more anteriorly than the natural crystalline lens equator 1.