Keratoplasty Types (PK, DALK, DSAEK, DMEK) Compared for Exams

The simplest way to answer a keratoplasty question is to name the diseased corneal layer and then choose the operation that replaces that layer while preserving healthy host tissue where appropriate. Penetrating keratoplasty (PK) is full thickness. Deep anterior lamellar keratoplasty (DALK) replaces anterior stroma while retaining host Descemet membrane and endothelium. DSAEK and DMEK are posterior lamellar/endothelial procedures, but their donor tissue differs.

That is the framework, not a patient-specific surgical rule. Choice of operation depends on the individual eye, diagnosis, anatomy, surgeon assessment, tissue availability and current practice. This article is for postgraduate theory and viva preparation; it does not teach a surgical procedure or recommend one for a patient.

Start with the corneal layer map

An examiner can hide the required operation inside the pathology. First decide where the problem sits.

The word predominant is important. A cornea can have more than one problem. The exam method is to identify the pathology the stem makes decisive, rather than treating any diagnosis as automatically linked to one procedure.

The anatomy you must be able to say aloud

From front to back, the cornea includes epithelium, Bowman layer, stroma, Descemet membrane and endothelium. The stroma makes up most corneal thickness. The endothelium and its pump function are central to corneal deturgescence. That is why a stromal disorder with healthy endothelium creates a different surgical conversation from endothelial decompensation.

Say the retained tissue explicitly. It is the easiest way to prevent the classic viva error of calling DALK “a partial PK” without explaining what is partial about it.

The four procedures at a glance

Memory line: “PK passes through; DALK leaves Descemet; DSAEK adds stroma; DMEK is membrane plus endothelium.” The line is deliberately compressed. After saying it, explain the tissue table. A mnemonic gets you to the correct branch; anatomy gets you the marks.

Penetrating keratoplasty: full-thickness means full-thickness

PK replaces a full-thickness corneal button. The AAO-hosted EyeWiki overview of PK is a useful educational reference for the core terminology and complications, while surgical decisions remain case-specific.

In an exam, PK is the contrast procedure. It is the answer when the question makes clear that pathology is full-thickness, structurally extensive, or not suited to retaining a healthy posterior layer. Do not state that PK is “obsolete” because lamellar surgery exists. Lamellar approaches preserve tissue where feasible; they do not remove the need for full-thickness transplantation in every complex cornea.

The key drawbacks worth naming in a viva are that a full-thickness graft involves an open-sky operation and carries issues such as wound integrity, suture-related problems, astigmatism, infection, raised intraocular pressure, graft failure and rejection. Do not produce a long complication list without separating categories. “Rejection” and “failure” are not synonyms: rejection is an immune event; failure describes loss of graft clarity/function and may have several causes.

Exam-ready sentence: “PK is a full-thickness graft. I would consider its role when the corneal pathology is full thickness or when a lamellar approach cannot preserve a suitable host layer; I would then discuss graft survival, rejection, astigmatism and wound-related risks in the appropriate clinical setting.”

DALK: preserve healthy endothelium when the disease is anterior

DALK removes diseased anterior corneal tissue while preserving the recipient Descemet membrane and endothelium. That retained host endothelium is the defining contrast with PK. A peer-reviewed DALK review describes its use in stromal pathology and the importance of the interface/Descemet plane.

The theory logic is straightforward: if the stroma is the major problem and the endothelium functions, an anterior lamellar approach may retain viable recipient endothelium. Typical exam contexts include keratoconus, anterior stromal scar and certain stromal dystrophies. The exact indication depends on the individual cornea; avoid the simplistic statement “keratoconus always gets DALK.” Scarring depth, prior hydrops, endothelial status and surgeon judgement affect a real decision.

The classic intraoperative issue is Descemet membrane perforation. In a viva, say it may alter the procedure or require conversion depending on extent and circumstances. Do not give a mandatory conversion rule unless an authoritative current surgical source and the stem justify it.

PK versus DALK: use retained endothelium as the discriminator

If the examiner asks for an advantage of DALK, the defensible anatomical answer is preservation of healthy host endothelium. Do not turn that into an unqualified claim of universally better vision, fewer complications or automatic superiority. Outcomes depend on diagnosis, technique, interface and follow-up.

Endothelial keratoplasty: DSAEK and DMEK

Endothelial keratoplasty addresses endothelial dysfunction by replacing posterior donor tissue while retaining most recipient stroma. It is the correct branch of the decision tree for a stem describing endothelial failure rather than a primary anterior scar.

DSAEK: the stromal-backed posterior lenticule

Descemet stripping automated endothelial keratoplasty (DSAEK) uses donor endothelium and Descemet membrane with a thin amount of posterior donor stroma. The stromal component is its simplest contrast with DMEK. A DSAEK review provides the foundational terminology and clinical context.

For exams, say “posterior lamellar endothelial graft with stromal support.” Do not merely call it “an endothelial transplant,” because both DSAEK and DMEK qualify and the question often asks you to distinguish them.

DMEK: Descemet membrane and endothelium only

Descemet membrane endothelial keratoplasty (DMEK) transplants donor Descemet membrane and endothelium without the stromal layer included in DSAEK. The DMEK review is a peer-reviewed source for that tissue distinction and its place in endothelial keratoplasty.

The high-yield comparison is tissue, not an overconfident outcome slogan. DMEK has a thinner donor graft than DSAEK. It also has its own technical and postoperative issues, including graft attachment/detachment and the potential need for an air/gas re-bubble procedure. State this as a recognised consideration, not as a prediction for every patient.

DSAEK versus DMEK: the table to redraw from memory

Memory hook: “DSAEK has the S for stroma; DMEK is DM plus endothelium.” It is not etymologically perfect, but it reliably preserves the tissue difference when you are under time pressure.

Indications: state pathology first, procedure second

An exam answer becomes clearer if you use this grammatical order:

“The pathology predominantly affects ___; the host ___ is functional/not suitable to retain; therefore I would compare ___ with ___.”

Examples:

• “In a stromal ectatic or scarred cornea with functional endothelium, I would compare DALK with PK.”
• “In endothelial dysfunction with suitable stroma, I would compare DSAEK and DMEK.”
• “With extensive full-thickness corneal pathology, PK may be the relevant graft category.”

This avoids a frequent teaching trap: listing indications as if each disease has one irrevocable operation. It also lets you answer an unfamiliar stem because the layer logic still works.

Fuchs endothelial corneal dystrophy is a common example of endothelial disease in exam questions. It is not enough to say “Fuchs equals DMEK.” The correct study statement is that endothelial keratoplasty is the relevant family to consider when endothelial dysfunction is the key pathology, with selection depending on the eye and current corneal-surgeon practice.

Complications and rejection terminology without mixing labels

Candidates often lose marks by using “graft rejection,” “graft failure,” “infection” and “raised pressure” as a single undifferentiated list. Sort them by mechanism.

The corneal transplantation review in StatPearls is a useful cross-check for general terminology. For an exam, do not claim a fixed complication rate unless the question gives a source and a population. Rates vary by indication, technique and era.

Six common viva traps

1. Calling DALK an endothelial procedure. It preserves host endothelium; it is an anterior/stromal procedure.
2. Forgetting the stromal component in DSAEK. This is the key contrast with DMEK.
3. Calling every corneal transplant “PK.” State whether it is full thickness, anterior lamellar or posterior lamellar.
4. Saying DMEK is always best. Thinner tissue does not erase case selection and technical context.
5. Confusing rejection with failure. Explain the category and the mechanism.
6. Answering a surgical choice without naming the diseased layer. The pathology-to-tissue chain is usually what the question is testing.

A one-minute comparison answer

“I classify corneal grafts by the tissue replaced. PK is full-thickness. DALK replaces anterior stroma while preserving recipient Descemet membrane and endothelium, so it is relevant when stromal disease occurs with functional endothelium. DSAEK and DMEK are endothelial keratoplasty procedures: DSAEK includes a thin posterior stromal component, whereas DMEK transfers Descemet membrane and endothelium only. I would choose the operation family from the diseased layer and then consider individual anatomy and current surgical practice.”

That answer has enough detail for a short viva and leaves room for the examiner to ask about a particular disease or complication.

Rapid revision grid

Before an exam, redraw this from memory:

Then review the cornea study guide for the surrounding disease framework. For practical-answer rehearsal, OSCE, Practical & Viva Voce Ready is the relevant site resource, and Handwritten Exam Ready Notes provides the broader revision collection. Product pages describe their own contents; none is a substitute for supervised surgical training or current clinical guidance.

Sources

1. Penetrating Keratoplasty, EyeWiki — AAO-hosted educational overview of full-thickness graft terminology and complications; checked 18 August 2026.
2. Deep anterior lamellar keratoplasty review — DALK tissue, indications and interface concepts; checked 18 August 2026.
3. Descemet stripping automated endothelial keratoplasty review — DSAEK graft composition and context; checked 18 August 2026.
4. Descemet membrane endothelial keratoplasty review — DMEK graft composition and endothelial-keratoplasty context; checked 18 August 2026.
5. Corneal Transplantation, StatPearls — terminology and complication cross-check; checked 18 August 2026.