The cornea is the transparent, dome-shaped tissue at the very front of the eye, which plays a primary role in focusing light onto the retina. When disease or injury causes clouding, scarring, or distortion, vision becomes impaired, often requiring a transplant procedure called keratoplasty. A lamellar keratectomy is a modern surgical technique that involves the selective replacement or removal of only the diseased layers of the cornea, preserving the healthy structures underneath. Targeting only the damaged portion while leaving deeper, healthy layers intact reduces surgical risks and improves the long-term prognosis.
Understanding Partial Thickness Cornea Surgery
The term “lamellar” refers to the layer-by-layer structure of the cornea, which is composed of five distinct layers. The outermost layer is the epithelium, which serves as a protective barrier against infection, followed by Bowman’s layer and the thick central stroma. The stroma makes up about 90% of the cornea’s thickness and provides its shape and strength.
The innermost layers are Descemet’s membrane and the endothelium, a single layer of specialized cells. Endothelial cells function like a pump, constantly moving water out of the stroma to keep the cornea in a state of relative dehydration necessary for optical clarity. Partial thickness, or lamellar, surgery is defined by its method of only removing the layers that are affected by disease, which is in contrast to a penetrating keratoplasty (PK).
A penetrating keratoplasty involves a full-thickness exchange, where the entire central cornea is cut out and replaced with donor tissue. Lamellar surgery preserves the healthy inner layers, particularly the endothelium. This selective approach maintains the structural integrity of the globe and significantly reduces the exposure of the donor tissue to the recipient’s immune system.
Conditions Requiring Lamellar Keratectomy
The decision to perform a lamellar keratectomy is based on the depth of the pathology within the corneal layers. Conditions predominantly affecting the anterior and middle layers are ideally suited for this procedure, including superficial scarring from injury, infections, or inflammation that have not penetrated the full thickness of the stroma.
Hereditary corneal dystrophies, such as Reis-Bücklers or granular dystrophy, deposit abnormal material within the anterior stroma, causing visual haze. Salzmann’s nodular degeneration, which causes elevated nodules on the cornea, is also treatable by removing only the superficial layers. In these cases, a superficial anterior lamellar keratectomy (SALK) may be performed to excise the diseased tissue.
The most common indication for a deep lamellar procedure is advanced keratoconus, where the central cornea progressively thins and bulges outward. Keratoconus primarily affects the stroma, but the innermost endothelial layer often remains healthy. Replacing the entire diseased stroma down to Descemet’s membrane restores the cornea’s proper shape and transparency while preserving the patient’s own healthy endothelial cells.
Differentiating Surgical Approaches
Lamellar keratectomy encompasses several distinct surgical techniques, with the choice depending on how deep the corneal damage extends. The two primary approaches are Anterior Lamellar Keratoplasty (ALK) and Deep Anterior Lamellar Keratoplasty (DALK). Both procedures aim to replace the diseased anterior stroma while preserving the patient’s endothelium.
Anterior Lamellar Keratoplasty (ALK) involves dissecting and removing the outer layers of the cornea down to a specific, predetermined depth within the stroma. This technique is reserved for pathologies strictly confined to the superficial or mid-stromal layers. The surgeon then transplants a corresponding partial-thickness donor graft onto the remaining healthy stroma and secures it with fine sutures.
Deep Anterior Lamellar Keratoplasty (DALK) is the more technically demanding procedure and is used when the pathology extends through almost the entire thickness of the stroma, such as in advanced keratoconus. The goal of DALK is to remove the stroma right up to the level of Descemet’s membrane, leaving only the patient’s Descemet’s membrane and endothelium intact.
A common method to achieve this precise separation is the “big bubble” technique, where a cannula is used to inject air or fluid into the deep stroma. The injected air creates a distinct bubble that hydraulically separates Descemet’s membrane from the overlaying stroma. This separation allows the surgeon to peel away the diseased stromal tissue cleanly, exposing the smooth, inner surface of the membrane. A full-thickness donor stroma is then placed over the exposed Descemet’s membrane, providing a new, transparent layer.
Postoperative Care and Visual Recovery
Following a lamellar keratectomy, the recovery process is generally more favorable than with a full-thickness transplant. The patient requires careful monitoring with anti-inflammatory and antibiotic eye drops to prevent infection and manage swelling. Initial healing often occurs within a few weeks, though maximum visual acuity may take several months.
Suture removal, if necessary, is a gradual process that begins months after surgery, adjusted based on the patient’s visual progression and corneal curvature measurements. The primary long-term advantage of lamellar procedures is the preservation of the patient’s own endothelium. Since the transplanted tissue is only stroma, the risk of immune-mediated graft rejection is substantially lower compared to a penetrating keratoplasty.
This reduced risk of rejection means patients require less prolonged use of high-dose corticosteroid drops, helping prevent complications like glaucoma and cataract formation. Lamellar procedures shift the focus to managing the healing of the stromal interface, resulting in an excellent long-term prognosis and a durable solution for anterior and mid-stromal diseases.