p.12
Surgical Techniques for Myopia Correction
What is the purpose of clear lens extraction?
To remove noncataractous lenses and insert an intraocular lens to correct spherical refractive errors.
p.12
Surgical Techniques for Myopia Correction
What is the effect of corneal incisions that are closer to the visual axis?
They have the greatest effect on central corneal curvature.
p.10
Surgical Techniques for Myopia Correction
What does the Epikeratophakia procedure involve?
Attaching a lenticule of pre-shaped donor corneal stroma to the surface of the host cornea.
p.10
Surgical Techniques for Myopia Correction
What is a key characteristic of the Epikeratophakia procedure?
The eye is not entered, and the procedure can be reversed by removing the lenticule.
p.11
Surgical Techniques for Myopia Correction
What type of refractive error can keratomileusis correct?
High degrees of myopia, but not hypermetropia.
p.13
Effects of Vitreo-Retinal Surgery on Refraction
What happens to the refractive index of the lens when silicone oil is present?
It changes the posterior surface of the lens from a converging to a diverging interface.
p.15
Angles Formed by Parallel Lines
What is true about the angles formed by parallel lines AB and CD intersecting line EF?
The angles α formed are all equal.
p.7
Surgical Correction of Astigmatism
What is the advantage of placing incisions wholly within the graft?
It conserves the wound and has a more predictable effect.
p.9
Surgical Correction of Astigmatism
What happens to corneal topography if compression sutures are removed?
The topography will change, potentially leading to overcorrection or degeneration.
p.14
Surgical Techniques for Myopia Correction
What advantage does gas filling provide for indirect ophthalmoscopy in a phakic eye?
It may allow indirect ophthalmoscopy without the use of a condensing lens.
p.9
Surgical Correction of Astigmatism
How can high degrees of astigmatism after penetrating keratoplasty be corrected?
By removing a deep arcuate wedge measuring 60–90° from the graft–host junction in the flattest meridian.
p.12
Surgical Techniques for Myopia Correction
What are phakic intraocular lenses used for?
To correct refractive errors in phakic eyes.
p.12
Patient Suitability and Expectations
What is a significant concern regarding phakic intraocular lenses?
The long-term effects on the corneal endothelium, crystalline lens, and iridocorneal angle are unknown.
p.11
Surgical Techniques for Myopia Correction
Why have keratomileusis and keratophakia not been widely adopted?
Because they are technically difficult and the refractive outcome is often unpredictable.
p.6
Surgical Correction of Astigmatism
What is a challenge in correcting post-keratoplasty astigmatism?
The meridia of maximum and minimum curvature may not be at right angles to each other.
p.13
Effects of Vitreo-Retinal Surgery on Refraction
What refractive change can occur due to the presence of silicone oil in the posterior segment of the eye?
It induces a hypermetropic shift in refraction of +5.00 to +7.00 D.
p.9
Surgical Correction of Astigmatism
How can relaxing incisions be combined to reduce large degrees of corneal astigmatism?
By placing compression sutures 90° away from them.
p.11
Surgical Techniques for Myopia Correction
What is keratomileusis?
The use of a microkeratome to remove a lamella of anterior corneal stroma, which is then shaped on a cryolathe before being replaced.
p.6
Surgical Correction of Astigmatism
How is the success of surgical correction of astigmatism often measured?
By the post-operative tolerance of spectacles or contact lenses to correct the residual refractive error.
p.13
Surgical Techniques for Myopia Correction
What determines the refractive outcome of penetrating keratoplasty?
The dimensions of the donor tissue.
p.14
Surgical Techniques for Myopia Correction
How does silicone oil compare to the crystalline lens in terms of convergence?
Silicone oil is more strongly converging than the crystalline lens.
p.10
Surgical Techniques for Myopia Correction
What material is used in the Intrastromal Corneal Ring procedure?
PMMA (Polymethyl methacrylate) split ring.
p.9
Surgical Correction of Astigmatism
What effect does a tight suture placed across the graft–host junction have?
It increases the curvature of the cornea and reduces astigmatism.
p.7
Surgical Correction of Astigmatism
Why are linear incisions less favorable?
They pass through cornea of varying thickness and parts are closer to the visual axis.
p.3
Patient Suitability and Expectations
How long does corneal topography change after discontinuing contact lens wear?
Fifteen weeks for PMMA, ten weeks for gas permeable, and five weeks for soft lenses.
p.13
Surgical Techniques for Myopia Correction
What is the effect of a graft whose diameter exceeds that of the tissue removed in penetrating keratoplasty?
It is more likely to result in myopia.
p.14
Surgical Techniques for Myopia Correction
What is the result of gas filling an aphakic eye?
It allows an unaided view of the fundus.
p.5
Surgical Techniques for Myopia Correction
What is the purpose of the radial incisions in the cornea?
To weaken the cornea and allow intraocular pressure to cause the wounds to gape and the cornea to bulge.
p.5
Surgical Techniques for Myopia Correction
What is the outcome for myopes of less than –5.00 D after radial keratotomy?
More than three-quarters end up within 1.00 D of emmetropia.
p.12
Surgical Techniques for Myopia Correction
What is the role of sutures in large corneal incisions?
They appose the wound edges and can induce or reduce corneal astigmatism depending on their tension.
p.13
Surgical Correction of Astigmatism
How does the small self-sealing incision in phacoemulsification cataract surgery affect the cornea?
It tends to flatten the cornea in the same meridian post-operatively.
p.13
Effects of Vitreo-Retinal Surgery on Refraction
What is the purpose of attaching a silicone buckle during vitreo-retinal surgery?
To indent the wall of the eye and repair a retinal detachment.
p.15
Mathematical Definitions
What are the three primary trigonometric functions mentioned?
Sine, Cosine, and Tangent.
p.10
Surgical Techniques for Myopia Correction
What is the purpose of the Intrastromal Corneal Ring (ICR) procedure?
To flatten the central corneal curvature and treat myopia up to –4.00 D.
p.7
Surgical Correction of Astigmatism
What is a recommended technique for correcting astigmatism after corneal graft sutures are removed?
Incising the graft–host junction over 60–90° where it crosses the steepest meridian.
p.11
Surgical Techniques for Myopia Correction
In what cases might epikeratophakia be useful?
In cases of aphakia or cataract where there is contact lens intolerance or an intraocular lens is contraindicated.
p.3
Photorefractive Keratectomy (PRK)
What technique uses an excimer laser to change the anterior curvature of the cornea?
Photorefractive Keratectomy (PRK).
p.3
Photorefractive Keratectomy (PRK)
What can cause haloes to be seen around lights after PRK?
If the diameter of the treated area is 3.5–4 mm.
p.9
Surgical Correction of Astigmatism
What are nomograms used for in astigmatic correction?
They relate the astigmatic correction from different combinations of clear zone diameter, incision arc, and the number of incisions.
p.10
Surgical Techniques for Myopia Correction
What types of refractive errors can be corrected with Epikeratophakia?
High degrees of hypermetropia and myopia.
p.2
Patient Suitability and Expectations
What is the consequence of creating anisometropia?
It may make work requiring stereopsis and good visual acuity impossible.
p.11
Surgical Techniques for Myopia Correction
What is the purpose of keratophakia?
To correct aphakia by replacing a lamella of anterior stroma over a shaped lenticule of donor corneal stroma.
p.11
Surgical Techniques for Myopia Correction
What is thermokeratoplasty?
A largely experimental procedure that induces contraction of collagen in the peripheral cornea to increase corneal curvature.
p.6
Surgical Correction of Astigmatism
What effect does a transverse or arcuate keratotomy have on the cornea?
It causes the cornea to bulge at the incision site, reducing surface curvature in that meridian.
p.9
Surgical Correction of Astigmatism
What effect do longer incisions or incisions closer to the visual axis have?
They have a greater effect on astigmatic correction.
p.4
Surgical Techniques for Myopia Correction
Why is excimer laser correction of hypermetropia more difficult?
More tissue must be ablated peripherally than centrally to make the cornea steeper.
p.10
Surgical Techniques for Myopia Correction
What must be ensured during the Epikeratophakia procedure?
That surgery does not alter the shape of the recipient cornea to avoid unwanted refractive error.
p.11
Surgical Techniques for Myopia Correction
How does epikeratophakia correct keratoconus?
By suturing a lenticule of uniform thickness onto the conical host cornea to compress it and return it to a more normal contour.
p.13
Surgical Correction of Astigmatism
Why are temporal incisions considered more astigmatically neutral?
Because the temporal limbus is further from the visual axis.
p.8
Surgical Correction of Astigmatism
What configurations are shown for corneal incisions?
Configurations for reducing astigmatism alone or in combination with radial sutures.
p.9
Surgical Correction of Astigmatism
What is the purpose of suturing the wound with nonabsorbable mersilene?
To shorten the cornea and steepen the curvature in that meridian.
p.12
Surgical Techniques for Myopia Correction
How do phakic intraocular lenses compare to corneal procedures?
They correct higher refractive errors more predictably while conserving accommodation.
p.12
Surgical Techniques for Myopia Correction
How do longer corneal incisions affect healing?
They are more unstable and slower to heal.
p.3
Photorefractive Keratectomy (PRK)
What strategy can be used to correct higher degrees of myopia in PRK?
Multiple concentric treatment zones with smoothing transitions.
p.13
Surgical Correction of Astigmatism
How can surgically induced astigmatism be used to neutralize pre-operative corneal astigmatism?
By placing the incision in the steeper axis.
p.14
Surgical Techniques for Myopia Correction
What effect does an encircling scleral buckle have on the globe?
It constricts the globe and increases the axial length.
p.4
Surgical Correction of Astigmatism
What is the purpose of an ablatable mask in astigmatism correction?
To shield the cornea and allow deeper ablation of the corresponding area.
p.11
Surgical Techniques for Myopia Correction
How is aphakia commonly corrected today?
By a secondary intraocular lens.
p.10
Surgical Techniques for Myopia Correction
Why is Epikeratophakia no longer used to correct myopia?
Because the refractive outcome was highly variable.
p.2
Effects of Vitreo-Retinal Surgery on Refraction
What factors can affect refraction post-surgery?
Ocular incisions, suture placement, scleral buckles, silicone oil, and intraocular gas.
p.13
Effects of Vitreo-Retinal Surgery on Refraction
What effect does the degradation of suture material have post-surgery?
It reduces tensile strength and may cause a gradual change in refractive error for up to a year.
p.14
Surgical Techniques for Myopia Correction
What effect does gas in the posterior segment of a phakic eye have?
It greatly increases the refractive power of the posterior surface of the lens and causes a large myopic shift.
p.7
Surgical Correction of Astigmatism
How can pre-existing corneal astigmatism be reduced during small incision cataract surgery?
By making the incision in the steepest meridian of the cornea.
p.14
Surgical Techniques for Myopia Correction
What happens to the refractive power of the cornea when gas fills an aphakic eye?
It makes the posterior corneal surface highly diverging and almost neutralizes the refractive power of the cornea.
p.12
Patient Suitability and Expectations
For which conditions is clear lens extraction advocated?
High myopia and hypermetropes with presbyopia.
p.4
Radial Keratotomy (RK)
What is the purpose of radial keratotomy (RK)?
To irreversibly flatten the central corneal curvature to reduce its refractive power.
p.12
Patient Suitability and Expectations
How does age affect corneal healing?
Corneal healing is significantly slower in older individuals than in younger ones.
p.12
Surgical Techniques for Myopia Correction
What happens if a suture is tighter than others?
It induces corneal astigmatism by increasing the corneal curvature in that meridian.
