A study recently published in BMC Ophthalmology compared the long-term outcomes of posterior capsular opacification (PCO) in highly myopic eyes between hydrophilic intraocular lenses (IOLs) and hydrophobic IOLs.
Give me some background.
High myopia is characterized by axial length [AL] ≥26 mm and is accompanied by early-onset cataract.
Patients with high myopia often show higher risks of complications after cataract surgery compared to emmetropic patients—with PCO being one of the most frequent long-term complications.
Why: Highly myopic eyes have larger capsular bags and thinner implanted IOLs, making it easier to form incomplete capsular-IOL interaction and thereby to develop PCO.
Bring in IOL designs.
Of note: Higher rates of PCO have been linked with specific IOL designs and materials, with IOLs with a square edge design potentially reducing the occurrence of PCO.
- Plus: In recent years, the hydrophilicity of IOLs has also gained attention as a risk factor for PCO in the normal population.
Consequently: The research team hypothesized that the hydrophilicity of IOLs may also affect the occurrence and severity of PCO.
Now talk about the study.
In this retrospective study, investigators included 679 highly myopic eyes (AL ≥26 mm) undergoing phacoemulsification with IOL implantation and divided the cohort into two groups:
- Hydrophilic IOL (n=613)
- Hydrophobic IOL (n=66)
The severity scores of PCO were evaluated using the EPCO 2000 software system, with both the areas of central 3.0 mm (PCO-3 mm) and of the capsulorhexis (PCO-CCC) analyzed.
Clinically significant PCO was defined as eyes with visual-impairing PCO or history of capsulotomy.
Findings?
The mean follow-up time was 34.7±12.3 months. Both PCO-3 mm and PCO-CCC scores were significantly higher in the hydrophilic IOL group compared with those of the hydrophobic IOL group (P<0.05).
The hydrophilic IOL group also had a shorter time to clinically significant PCO development (P=0.029).
Higher scores of PCO-3 mm and PCO-CCC in highly myopic eyes were both associated with (P<0.05):
- Hydrophilicity of IOL
- Longer follow-up duration
- Worse postoperative best-corrected visual acuity (BCVA)
Anything else?
Patients with a hydrophilic IOL and younger age showed higher risk of clinically significant PCO.
In extreme myopia (AL >30 mm), hydrophobic IOLs reduced PCO risk by 41% (hazard ratio [HR]: 0.59, p=0.003).
Patients with hydrophilic IOLs had a shorter time to PCO-related visual impairment (41.8 vs. 84.0 months), indicating the clinically significant PCO occurs earlier.
Expert opinion?
The study authors noted that the surface of hydrophilic IOLs has been confirmed to promote the proliferation and migration of lens epithelial cells into the visual axis, potentially amplifying PCO severity in eyes with suboptimal capsular coverage or minor intraoperative stress.
Conversely: Hydrophobic IOL can adhere to the collagen membrane, making the IOL tightly connected to the capsular bag, reducing the space for the migration of residual cells, and thus lowering the occurrence of PCO.
- Long story short: The study authors speculated that reduced bioadhesion in hydrophilic IOLs may exacerbate PCO severity.
Any limitations?
A few to note, including:
- The retrospective and non-randomized design introduced the potential for selection bias, as IOL selection was based on surgeon preference and inventory, preventing causal inference
- Unmeasured factors such as AL and potential differences in IOL edge sharpness could also have influenced PCO outcomes
- The significant imbalance in group sizes reduced the statistical power for the hydrophobic cohort, which decreased the statistical power for that group and limited the generalizability of findings
- This study did not account for variations in capsulorhexis size, surgical technique, or specific ophthalmic viscosurgical device (OVD) types due to data constraints
- There was a lack of data on capsulorhexis size and the consequent overlap with the IOL optic, which are well-established major determinants of PCO; their absence means that the observed effect sizes for IOL hydrophilicity may be confounded by variations in these surgical parameters
- The binary definition of clinically significant PCO has inherent limitations, as the EPCO score cutoff of 0.127, while specific, has only modest sensitivity
- Nd:YAG capsulotomy can be subjective and influenced by surgeon preference and patient tolerance, which were not standardized in this study
Take home.
These findings suggest that in highly myopic patients, the hydrophilicity of IOL correlates with earlier and more severe postoperative PCO in the long-term.
This study may bring new insights into the selection of IOL types and management of postoperative complications.
Next steps?
The study authors noted that future studies should prospectively:
- Compare next-generation IOL materials in high myopia
- Investigate mechanistically how chronic inflammation in myopic eyes modulates IOL-capsule interactions using in vitro models
- Standardize capsulorhexis size and surgical techniques in controlled trials to isolate material-specific PCO effects and pharmacological adjuvants to mitigate PCO risk with hydrophilic IOLs in high-risk patients