Comparative graft survival and visual outcomes of penetrating keratoplasty versus lamellar keratoplasty: A retrospective cohort study

The human eye relies on a clear, window-like structure at the front called the cornea to focus light and create sharp images. When disease, injury, or genetic conditions damage this window beyond repair, vision fades. For decades, the standard solution has been to replace the entire damaged window with a healthy one from a donor. This full-thickness swap, known as penetrating keratoplasty, has saved sight for countless people. However, like any major surgery, it carries risks, including the body rejecting the new tissue or the eye developing high pressure that can damage the optic nerve. In recent years, surgeons have developed a more selective approach called lamellar keratoplasty. Instead of swapping the whole window, this technique removes only the specific damaged layers while leaving the healthy inner lining of the patient's own eye intact. The hope has been that by preserving more of the eye's natural structure, this newer method would lead to fewer complications and better long-term vision, but the medical community has needed real-world data to confirm if this is truly the case across different types of patients.

Researchers at King Abdulaziz Medical City in Riyadh set out to compare these two approaches by looking back at the medical records of 255 eyes that underwent corneal transplants between 2016 and 2023. The team examined patients who received either the traditional full-thickness replacement or the newer, partial-thickness procedure. They tracked how long the new corneas lasted before failing, how well patients could see after surgery, and whether complications like high eye pressure arose. The study focused on a diverse group of patients with various eye conditions, ranging from corneal scarring and infections to a condition where the cornea thins and bulges outward, known as ectasia. By analyzing this large collection of cases, the researchers aimed to determine if one surgical technique was objectively superior to the other in terms of survival and visual recovery.

The initial numbers told a story that seemed to favor the newer, partial-thickness method. In the group of eyes that received the full-thickness transplant, about one in five eventually experienced graft failure, meaning the new cornea became too cloudy to see through or required a second surgery. In contrast, only a tiny fraction of the partial-thickness group faced this same fate. At first glance, it appeared that the selective technique was far safer. However, a closer look revealed that the two groups of patients were not starting from the same place. The partial-thickness group was made up almost entirely of patients with the bulging cornea condition, a disease that typically leaves the deepest layer of the eye healthy and thus ideal for the selective procedure. The full-thickness group, on the other hand, included many patients with severe scarring, infections, or failed previous surgeries, conditions that are much harder to treat and carry a higher risk of failure regardless of the technique used.

When the researchers adjusted for these differences, the picture changed significantly. They isolated the patients who had the bulging cornea condition and compared the two techniques only within that specific group. In this fairer comparison, the survival rates were nearly identical, with both methods showing excellent results. The statistical analysis confirmed that the surgical technique itself was not the deciding factor in whether a graft would fail; rather, the underlying reason for the surgery and the patient's specific eye history were the true drivers of the outcome. This suggests that the apparent advantage of the newer method was not because the surgery was better, but because it was being used on patients who were already more likely to succeed.

Visual outcomes, however, told a slightly different story. Patients who received the partial-thickness surgery were more likely to achieve good vision, with over 70 percent reaching a level where they could see clearly enough to drive, compared to less than half of those who received the full-thickness transplant. The researchers noted that this difference might be partly due to the fact that many patients in the full-thickness group had more complex eye damage to begin with. Additionally, the study found an unexpected finding regarding eye pressure. While previous studies often suggested that partial-thickness surgeries caused less pressure buildup, this specific group of patients saw a larger increase in eye pressure after the partial-thickness procedure compared to the full-thickness one. The authors cautioned that this result might be influenced by how the patients were managed after surgery or the specific mix of conditions in their group, and it does not necessarily mean the technique is inherently more likely to cause pressure issues.

The study concludes that the choice between these two surgical methods should be guided primarily by the specific disease affecting the patient's eye, rather than a blanket assumption that one technique is universally better. For conditions where the inner lining of the cornea is healthy, the selective approach offers a way to preserve the eye's natural structure without sacrificing the chance for a successful transplant. For more severe damage involving the entire thickness of the cornea, the traditional full-thickness replacement remains the necessary and effective standard. The research highlights that while the newer technique has gained popularity, its success is deeply tied to selecting the right patients for the right reasons. Future studies with longer follow-up periods and more consistent data collection will be needed to fully understand the long-term benefits and risks, but for now, the evidence points to a tailored approach where the surgeon matches the technique to the specific needs of the individual eye.