Deep Anterior Lamellar Keratoplasty (DALK)The Procedure Is Technically Skilled And Involves Dissecting The Cornea To Almost 95% Thickness, And Removing The Top Layer. A Donor Corneal Button Is Prepared By Removing Descemet's Membrane And Donor Endothelium. The Donor Graft Is Then Sutured To The Host. The Cornea Takes A Little Longer To Clear But Visual Results Can Be Similar To Those Of A Penetrating Keratoplasty.
Deep Anterior Lamellar Keratoplasty (DALK), Is A Newer Method Of Corneal Surgical Procedure That Selectively Removed The Diseased Anterior Layers Of The Cornea And Retains The Healthy Innermost Layer (Endothelium). As The Inner Layer Is Retained The Body Does Not Recognize The Donor Tissue, Hence There Is No Risk Of Rejection, And Steroid Medications Need Not Be Continued For A Long Duration.
- Closed Eye Surgery
- No Chance Of Blinding Endothelial Rejection (By Retaining The Recipient's Own Endothelial Layer)
- Can Always Perform A Penetrating Keratoplasty If Visual Results Are Not Satisfactory
- Technically Challenging
- Potential For Interface Scarring (And Reduced Visual Clarity)
IndicationsDALK Can Be An Effective Treatment For Any Pathology Of The Anterior Cornea As Long As The Patient Has An Intact, Functioning Endothelium. Common Indications For DALK Include Keratoconus And Corneal Scars. Patients With Keratoconus Are Good Candidates For DALK Because They Are Typically Young And Have Healthy Endothelium. These Patients Stand To Lose The Most From The Occurrence Of Post-PK Immunological Reactions That Can Compromise Endothelial Function In Up To 20 Percent Of Cases. Less Common Indications For DALK Include Vernal Keratoconjunctivitis, Corneal Dystrophies And Ocular Surface Diseases With Limbal Stem Cell Deficiency, Including Stevens-Johnson Syndrome, Ocular Cicatricial Pemphigoid
Performing DALKVarious Approaches For Performing DALK Have Been Described In The Literature. One Method Is To Remove The Host Anterior Corneal Tissues Layer-By-Layer Until Reaching The Deep Stroma Or The Bare Descemet’s Membrane. Although Different Surgical Techniques Vary In Their Details, The Basic Surgery Consists Of The Following Steps:
Recipient Eye. The Anterior Corneal Surface Is Cut With A Suction Trephine Set To A Depth Of About Two-Thirds Of The Corneal Thickness. Then The Stromal Layers Are Dissected With A Rounded Blade, Angled Parallel To Descemet’s Membrane. Fluid Or Air Is Then Injected Using Either A 27- Or 30-Gauge Cannula In Between The Deep Stroma And Descemet’s Membrane To Separate Those Layers.
Because Early Techniques Failed To Visualize The Depth Of Stromal Dissection, There Was A Greater Risk Of Perforation Than When Descemet’s Membrane Can Be Visualized. New Techniques Described Below Can Decrease Surgical Times While Improving The Safety And Success Rates Of DALK:
- Intrastromal Air Injection. One Innovation In DALK Has Been The Use Of An Air-Filled Tuberculin Syringe, The Needle Of Which Is Injected Obliquely Into The Stroma Prior To Trephination. This Intrastromal Air Renders The Cornea Opaque And Provides A Safe Deep Interface For The Trephine.
- Hydrodelamination. After The Initial Trephination To About 75 Percent Of The Corneal Thickness, The Surgeon Can Inject Balanced Salt Solution Through A Cannula Into A Small Pocket Created In The Central Stroma. The Saline Induces Stromal Fiber Swelling, Which Facilitates Fine Manipulation With Forceps.
- Viscoelastic Dissection. After An Initial 80 To 90 Percent Trephination, Sodium Hyaluoronate Can Be Injected Through A Blunt Cannula Deep Into The Central Corneal Lamella Near Descemet’s Membrane. Injection Of The Viscoelastic Substance Between The Deep Stroma And Descemet’s Membrane Facilitates The Separation Of The Final Layers.
- Big Bubble. With The “Big Bubble” Technique, Air Is Injected Deep Into A Groove Created By Trephining 60 To 80 Percent Stromal Thickness. This Introduction Of Air Into The Stroma Anterior To Descemet’s Membrane Creates A Dome-Shaped Detachment Of Descemet’s Membrane, Which Is Then Identified By A Ring Visible With The Microscope.
- Anterior Chamber Air. In Order To Obtain The Best Visualization During The Surgery. This Injected Air Creates A Mirrorlike Effect That Facilitates The Movement Of Surgical Instruments Between Descemet’s Membrane And The Deep Stroma. Furthermore, The Air-To-Endothelium Interface Becomes A Landmark To Identify The Posterior Surface Of The Cornea, Serving As A Reference For Dissection Depth.
- Donor Eye. Although Preserved Grafts Can Be Used, Most Of The Literature Reports Use Of Fresh Corneas Prepared By The Surgeon. Descemet’s Membrane And Endothelium Are Removed By Gently Swabbing The Posterior Corneal Surface Of The Donor Corneoscleral Rims With Dry Cellulose Sponges. Forceps Also May Be Used For Removing The Posterior Corneal Layers. Then A Corneal Button Is Punched Out From The Tissue. Suturing Technique Be Done According To The Surgeon’s Preference In DALK, Just As In PK. After Suturing, A Bandage Soft Contact Lens Is Placed On The Cornea.
ComplicationsThe Most Frequently Encountered Complication Of DALK Is Perforation Of Descemet’s Membrane And Entering The Anterior Chamber From The Stroma. Descemet’s Membrane And The Posterior Cornea Are Especially Susceptible To Perforation By Sharp Instruments. Tears Or Perforations Occur In Approximately 10 To 30 Percent Of Cases. The Viscoelastic Dissection Technique May Offer Some Protection Against Perforation.
If A Perforation Occurs, Management Depends On The Timing And The Size Of The Injury. If The Tear Occurs While The Stroma Still Covers Descemet’s Membrane, It Generally Self-Seals.
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