NOBC 2025 SESSION F - SURGICAL FACTOR/SIA/ A-CONSTANT

1. Regarding surgical factor

• A. The placement of IOL in the sulcus and posterior chamber will produce a different result

• B. The anterior placement of IOL enhances it’s refractive effect, the power should be 0.5-1.0D higher in sulcus IOL compared to PCIOL

• C. The shorter diameter of CCC tends to shift the IOL more anteriorly post operatively

• D. Retained viscoelastic can cause displacement of the IOL

Answer explanation

B. False: The anterior placement of IOL enhances it’s refractive effect, the power should be 0.5-1.0D lower in sulcus IOL compared to PCIOL

C. False: The larger diameter of  CCC tends to shift the IOL more anteriorly post operatively

2. Which of the following statements is/are true about SIA

• A. The tight corneal suture lead to SIA

• B. Larger wound causes more SIA as compared to smaller wound

• C. Temporal corneal wound cause more SIA as compared to superior wound

• D. SIA will cause changes in the pre-operative corneal astigmatism axis

Answer explanation

C. False: Superior wound causes more SIA due to the anatomical corneal diameter

3. Which of the following are the issues encountered with SIA calculations

• A. Most machine does not calculate posterior curvature

• B. Astigmatism is a vector where it has its own magnitude and direction

• C. Patient’s biological responses such as healing do not play role in the SIA calculations

• D. Wound incision may cause a change in power and axis

Answer explanation

C. False: Patient’s biomechanical issues such as healing do play role in the SIA calculations

4. Factors affecting A-constant include

• A. IOL design

• B. Intended location within the eye

• C. Axial length

• D. Keratometry

5. 5. Regarding effective lens position (ELP)

• A. Explains position of the IOL pre- and postoperatively

• B. All IOL formula require ELP

• C. Errors can lead to refractive surprise

• D. ELP increase in longer eyeball

Answer explanation

A. False: Explains position of the IOL postoperatively