Week 6 - Refractive Procedures Flashcards
What is Laser vision correction?
• Involves reshaping cornea by removal of corneal tissue
• Reduces or eliminates need for spectacles or contact lenses
• most common procedures : LASIK and LASEK
• For Myopia, Hyperopia and astigmatism
What is the excimer laser, and how does it work?
• UV laser using inert gas and reactive gas
• Pseudo-molecule created called Excimer
- Needs electricity, can only exist in energised state
• UV light from excimer well absorbed by biological matter, disintegrates it into air in tightly controlled manner referred to as ablation
• Excimer lasers can remove fine layers of surface tissue - with no heating or “change” to surrounding tissue
How is the stromal reshaped depending on cornea+ depth of cornea?
• Myopic errors require overall corneal flattening
• Hyperopic errors require corneal steepening
• Lasik requires 480um
- Ablation + flat thickness (120um)
• Lasek requires 450um
- Ablation
What does LASIK stand for and what is it?
• Laser assisted In Situ Keratomileusis
- Kerat = cornea Mileusis = carving
• Requires superficial corneal flap to be created prior to ablation with excimer laser
• Most commonly performed Laser Vision correction (Approx 90%)
• For Myopia, Hyperopia and astigmatism
What is the Lasik flap, and how is it done, and what are the benefits?
• Femtosecond laser is modern day method to create
- This is because Flap thickness created by Intralase typically thinner than mechanical microkeratomes (100-120um)
• Microkeratome - old tech (160um)
• Controlled Flap Structure
• Uniform Flap Thickness
• Superior Visual Outcomes
What are the 6 steps of LASIK?
- Cornea anaesthetised, lid speculum inserted
- A suction ring is applied to limbus to create an immobile cornea
- The flap is created by IntraLase
- Flap is lifted to expose stromal bed, the hinge most often being placed at 12 o’clock
- Eye tracker is engaged and the excimer laser is applied
- The flap is washed with balance salt solution, replaced, and the edges are smoothed down
What does LASEK stand for and what is it?
• Laser Assisted Sub Epithelial Keratectomy
- PRK = Photorefractive Keratectomy
• Incorporates certain elemets of LASIK surgery
• Instead of Corneal flap, the corneal epithelium is loosened and moved aside
• Many surgeons simply discard epithelium instead of repositioning it (Makes it PRK)
What are the 7 steps of LASEK?
- cornea is anaesthetised and a lid speculum inserted
- 18% Ethanol is applied to the cornea in a corneal ring for around 30 seconds to loosen the epithelium
- The edge of the loosened epithelium is lifted with a surgical instrument
- The stromal bed is exposed and the laser is applied immediately
- Mitomycin C may be applied to reduce the risk of haze
- The epithelium is replaced (becomes PRK if the epithelium is discarded)
- A bandage contact lens is applied which is removed by the Optometrist between day 3-5
What is an Implantable Collamer lens? (ICL)
• Alternative to laser vision correction for treatment of px c high ametropia, or other features that result in laser vision correction procedure not possible
• Clear implantable lens placed either between cornea/iris or behind iris, without removing natural lens of eye
• For Myopia, Hyperopia and astigmatism
What are the 6 steps of implantable collamer lens?
- Small incision in cornea, and two paracentesis at 10 and 2 O’clock for needles
- Viscoelastic material injected through incision to create deep anterior chamber
- IOL introduced to anterior chamber through incision + centred over pupil
- Fixation of IOL done by gently creating iris fold and manipulating IOL claw beneath fold
- Viscoelastic material removed and wound closed
- Prophylactic iridectomy may carry out to prevent pupil block glaucoma (Hyperopic px)
What is a implantable Collamer Lens, contraflow and differences between the myopic/hyperopic subtypes?
• Made from collamer : a 100% biocompatible material
• Myopic version of lens has “contraflow” technology, basically a small hole in centre of lens to aid aqueous out-flow
- Contra-flow designs a PI is not required pre-op.
• Contraflow not available for correction of hyperopia, therefore PI requires with px
What is refractive lens exchange??
• Refractive Lens Exchange, Natural Lens Replacement and modern day Cataract Surgery are identical procedures
• For myopia, astigmatism, hyperopia and presbyopia
• Misty natural lens removed, new IOL inserted
What are the 10 steps in refractive lens exchange?
- A mydriatic is instilled to achieve pupillary dilation.
- An incision is made into the eye approximately 1mm inside of the limbus.
- One 1mm paracentesis is made.
- Viscoelastic material is injected into the anterior chamber to protect the endothelium.
- An anterior capsularhexis is formed using forceps to expose the crystalline lens.
- The crystalline lens is broken down and aspirated.
- The capsular bag is filled with viscoelastic material.
- The lOL is implanted and unfolded into the bag using specially designed forceps.
- The haptics of the lens are secured in the capsular bag and the viscoelastic material is
- The incision is closed
LEFT OFF SLIDE 24
What is the Catalys Femtosecond laser?
• Creates incisions/corrects corneal astigmatism
