· Involves resecting the host stromal pathology (leaving the Descemet’s membrane and endothelium intact), and transplanting a complementary donor stromal button.
INDICATIONS:
· Ectasias:
o Keratoconus
o PMD
o Progressive post LASIK ectasia
· Hereditary stromal dystrophies
· Corneal scars sparing the DM
· Infectious keratitis
· Tectonic: Descemetocele
CONTRAINDICATIONS:
Corneal conditions with diseased endothelium.
Pre-existing rupture in DM.
Deep scars however small involving the DM.
Macular corneal dystrophy is a relative CI because of fragile nature of DM.
TYPES OF DISSECTION:
· Layer by layer manual dissection: A variable amount of stroma is left behind, therefore, the interface between the donor and recipient is intrastromal. Can impede visual acuity due to visible interface haze.
· Air-assisted manual dissection (Archila technique)
· Air guided deep stromal dissection (Melles’ technique)
· Anwar’s big bubble technique: apposition of the donor button to the bare DM provides an interface of high quality.
· Viscoelastic dissection
· Hydrodelamination
ADVANTAGES:
Non-penetrating surgery: reduces the risk of intraocular complications such as glaucoma, cataract formation, CME, RD, endophthalmitis and expulsive hemorrhage.
Retains the normal recipient endothelial layer, reducing the risk of endothelial graft rejection.
Does not require good endothelial quality donor tissue.
As the integrity of the Descemet's membrane is not disturbed, ALK technically achieves a stronger corneal wound
Suture related astigmatism is lesser.
DISADVANTAGES:
More demanding and time consuming.
Steeper learning curve.
Suboptimal visual acuity compared to PK if there are interface problems.
Lamellar dissection regularity.
Residual scarring.
PREOPERATIVE ASSESSMENT:
Detailed slit lamp biomicroscopic evaluation of the corneal pathology to assess depth of stromal involvement is to be done.
Pachymetry and AS-OCT indicating depth of involvement of the corneal pathology is recorded.
Preoperative assessment of lid and ocular adnexa, precorneal tear film, rule out presence of infection/inflammation, posterior segment evaluation and intraocular pressure.
General systemic evaluation may be required in cases to be operated under general anesthesia.
ADVANTAGES OF DALK OVER PK:
Elimination of the graft- host stromal interface, and the associated haze and irregularity.
Faster visual rehabilitation.
The visual outcomes of deep lamellar keratoplasty have been found to be comparable to standard penetrating keratoplasty with the endothelial cell loss also being reported to be equal to that of penetrating keratoplasty.
COMPLICATIONS:
INTRAOPERATIVE:
· Irregular lamellar bed: gives rise to astigmatism and poor optical quality of vision.
· Perforation of posterior stroma/DM
· Graft-host malapposition/ edge irregularity
· Interface debris
POSTOPERATIVE:
· Persistent epithelial defect
· Graft infection
· Recurrence of primary pathology (if HSV)
· Graft rejection (less common than in PK as host endothelium is preserved)
· Graft vascularisation
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Image from Rajan Eye Care Hospital