Cataracts are the leading cause of blindness worldwide, and phacoemulsification combined with intraocular lens implantation has become the most mainstream surgical approach. With advancements in surgical techniques and equipment, this procedure has evolved from a simple vision-restoring surgery into the era of refractive surgery. Patients now have higher expectations for postoperative visual quality, particularly the recovery of early vision, which directly impacts their satisfaction. Intraoperative surgical details have a direct influence on postoperative visual acuity.

Thanks to intraoperative optical coherence tomography (iOCT) technology, surgeons have gradually recognized that factors such as surgical incisions and intraoperative anterior chamber collapse can affect the survival of corneal endothelial cells after surgery, which is directly related to early postoperative vision and patient satisfaction. Swept-source intraoperative OCT (SS-iOCT) has further improved imaging range and clarity, helping us discover that the depth of intraoperative ultrasound energy use (such as cumulative dissipated energy) correlates with postoperative corneal endothelial cell loss. This suggests that compared to performing phacoemulsification at the capsular opening plane or in the anterior chamber, intracapsular phacoemulsification may reduce postoperative corneal endothelial cell loss, potentially leading to better early postoperative vision, which is crucial for patient satisfaction. However, evidence is still lacking.

Therefore, this study aims to compare the effects of intracapsular versus extracapsular phacoemulsification on early postoperative vision, as well as long-term visual acuity, corneal endothelial cells, corneal changes, and the incidence of intraoperative and postoperative complications.

Inclusion Criteria:

• Age ≥ 50 years and ≤ 90 years
• Able to cooperate with preoperative examinations
• At least one eye meets the study eye criteria
• Has the capacity and willingness to provide informed consent
• Age-related cataract
• Nuclear opacity (N) graded ≥4 according to the Lens Opacities Classification System III (LOCS III)
• Scheduled for phacoemulsification with intraocular lens implantation
• Pupil size ≥6 mm after dilation
• Corneal endothelial cell density ≥1500 cells/mm²

Exclusion Criteria:

• Considered unsuitable by the investigator for participation in this clinical trial for other reasons (e.g., unstable systemic condition, uncontrolled blood pressure/blood glucose, severe cardiovascular disease, renal disease, etc.)
• Blood pressure > 180/110 mmHg (systolic >180 mmHg or diastolic >110 mmHg). Patients may be considered for inclusion if blood pressure can be controlled below these thresholds with medication.
• History of myocardial infarction or other cardiac disease requiring hospitalization, cerebral infarction, transient ischemic attack, or acute heart failure within 4 months prior to enrollment.
• Women with childbearing potential (i.e., currently pregnant, breastfeeding, or planning to become pregnant within the next 2 years). Women of childbearing potential should be asked about the possibility of pregnancy, and the investigator will determine when a pregnancy test is necessary.
• Currently participating in another clinical trial
• History of ocular trauma or surgery
• Presence of other ocular diseases (e.g., glaucoma, diabetic retinopathy)
• Other ocular factors that may complicate surgery (e.g., small pupil, shallow anterior chamber)