Superficial anterior lamellar keratoplasty (SALK) surgery is used to treat astigmatism, stromal scarring, or opacities located in a third of the anterior stroma (such as Reis-Buckler), surface irregularity, and keratoconus (stromal thinning). SALK is a subcategory of lamellar keratoplasty, which is involved with selectively removing and replacing diseased corneal layers.
In SALK, the surgeon removes and replaces the diseased anterior corneal stroma with similar thickness, and in some cases, the epithelium is removed and replaced. However, in keratoconus, there is no need to remove the stromal tissue before replacement with donor stromal lenticule. SALK uses human fibrin glue and is a procedure that does not employ sutures. These factors account for the decreased incidences of graft rejection and reduced intraoperative complications.
SALK carries certain advantages. It avoids the interface haze that results from interface irregularities brought about by manual dissection. Whereas phototherapeutic keratectomy (PTK) can remove anterior scarring, the scar often ablates differently. Besides, PTK patients need to take topical corticosteroids for several months, and more scarring may follow. SALK minimizes all these risks involving scarring.
Candidates for SALK may include those with:
- Post keratitis scars
- Stromal dystrophies
- Post-traumatic scars
- Severe scarring after PRK
- Post–chemical injury scars
- Trachomatous keratopathy
- Epithelial-stromal TGFBI dystrophies
- Salzmann nodular degeneration (SND)
- Epithelial ingrowth that recurs after laser in situ keratomileusis (LASIK)
However, the following conditions are unsuitable for SALK:
- Active uveitis can cause inflammation and lead to graft failure.
- Uncontrolled glaucoma can interfere with graft healing or can result in primary graft failure.
- Deep-set eyes and eyes with a small palpebral aperture pose difficulties in using the microkeratome to prepare the host bed.
- Corneal endothelial disorder. SALK is only considered when the endothelium is healthy. A full-thickness PK would do in such circumstances.
- Deep scars that cover more than a third of the anterior corneal stroma should not be considered. Such scars may require a full-thickness PK or DALK.
- Systemic conditions can impair healing and interfere with graft uptake. These conditions include immune-compromised conditions, collagen vascular disease, and uncontrolled diabetes.
- Ocular surface disorders like lid abnormalities and dry eyes can lead to failure of the graft. For example, recurrent tear film breakdown can interfere with the healing process and cause graft failure. The disorder needs to be treated first before SALK can be performed.
Three types of instruments are used in surgery leading to SALK techniques being categorized as:
- Hemiautomated SALK
- Microkeratome-assisted SALK
- Femtosecond laser-assisted SALK
Before the Procedure
A thorough preoperative evaluation is mandatory. History and clinical examination are taken to rule out any systemic conditions that may interfere with the procedure. History includes any ocular surgery, visual demands, ocular conditions, occupation, and systemic medications. The following ocular examinations will be done:
- Visual acuity
- Intraocular pressure (IOP)
- Use of pachymetry to measure corneal thickness
- External eye examination to check for dry eye and lid abnormalities
- Tear film assessment using the Schirmer’s test. The assessment also includes the tear film breakup time
- Slit lamp biomicroscopy to assess the tear film, previous surgical scars, status of the endothelium, and depth of opacity (using anterior segment optical coherence tomography)
- Visual potential because pre-existing amblyopia can interfere with postoperative visual gain. The ophthalmologist uses a thorough fundus examination, potential acuity meter, and laser interferometry to assess visual potential
SALK is performed under general or local anesthesia. The type of anesthesia used depends on the age and cooperation of the patient. The SALK procedure takes place in two stages. In stage one, the surgeon obtains a pachymetry. S/he removes a large flap using a microkeratome head and repositions it in a process similar to a routine LASIK. The patient is released to go home to return six weeks later for the second procedure.
In the second part of the surgery, with the patient under local anesthesia (can prevent scar formation), the surgeon:
- Uses a vacuum trephine to make a partial-thickness cut through the LASIK-style flap and leaves a 1mm flap rim
- Peels away the flap (section of lamellar) that has been trephined
- Replaces the flap with donor tissue of the same size
- Uses a microkeratome head to create a corneal donor cap. S/he then cuts the cap with a trephine
- Places the donor cap on the recipient’s bed
- In microkeratome-assisted SALK, the surgeon sutures the donor graft into the recipient bed
- Places a bandage contact lens
- May use intraoperative keratometry to position the donor tissue and minimize astigmatism
In femtosecond laser-assisted SALK, the surgeon uses an anterior segment optical coherence tomography to measure the corneal pathology's depth. S/he uses a femtosecond laser to create the lamellar cut. The surgeon then removes the scarred tissue and replaces it with the donor lenticule of the cornea. S/he dries the incision, checks the adhesion of the flap, and places a bandage contact lens. No sutures are used.
Risks & Complications
SALK is a minimally invasive procedure; therefore, the risks and complications are limited primarily because no sutures are used in some of the SALK procedures. There is no graft rejection. However, complications associated with Femtosecond laser-assisted SALK may include:
- Dry eye
- Suspicious ectasia
- Epithelial ingrowth
- Recurrence of pathology
- Residual corneal pathology
- Irregular astigmatism which can limit visual improvement
Aftercare & Recovery
The patient will need topical corticosteroid drops to be administered every two hours for ten days. The drops will be tapered over the next six to eight weeks, depending on the patient's condition.
The first follow-up visit will take place the day after the procedure. The next visit takes place a month later and for several years, according to the surgeon's instructions.
SALK improves vision when it minimizes ectasia after refractive surgery and keratectasia in keratoconus patients. One study reported improved best-corrected visual acuity in 100% of the operated eyes, with 80% of the eyes improved within the first month. There was also an improvement in refractive astigmatism by 0.7 diopters.