RYAN VOLUME 3 - The biomechanics of Escleral Buckle in the treatment of RD #101 Flashcards
After a circumferential buckle, how is the horizontal and sagittal cross-section of the eye?
A prolate spheroid.
How can the anteroposterior axial posterior decrease after a buckle?
If the buckle is too tight and high.
How do the mattress sutures alter the axial length?
They shorten the AL.
What else contributes to a shift towards myopia?
Shallowing of the anterior chamber associated with displacement of the lens anteriorly (It may become less pornouced over time). There is also a reduction in the trabecular iris angle.
In which case does the buckle height decrease more: radial buckle or circumferential buckle?
Radial buckle.
What tends to happen when placing a buckle in a child?
It may retard growth-related increases in the axial length of the eye, causing the eye ti develop less myopia than the fellow eye.
Over time, the change in refractive error induced by the scleral buckle tends to normalize. Why?
- Stress relaxation of the band over time.
- The scleral invagination of the sutures decreases.
Which is shorter:: the scleral chord or the scleral arc?
The scleral chord is always shorter than the scleral arc. The longest the scleral chord, the highest difference to the the scleral arch lenght.
What is the lenght of the sutures that ensures maximum tension?
4 to 5 mm long (with deep bites).
Major variables that determine the internal geometry of the indentation:
- Shape of the buckle
- Composition of the buckle (silicone, sponge, hard silicon)
- Suture placement
- Suture tension
- Distribution of the tension from the suture
- IOP
Which buckle causes more fishmouth phenomenon: radial/wedge shaped buckle or encircling buckle?
Encircling buckle.
Anterior vitreoretinal traction, funnel-shaped retinal detachments: which is the best buckle?
Circumferential buckle.
How is the vitreous cavity volume after a bukcle?
It is reduced. A sphere contains the largest volume of fluid with the least surface area.
A 2.5 mm wide silicone encircling band displaces about _________ of the vitreous cavity volume.
0.5 mL or 12%.
Elastic bands width and height:
#40
#240
#41
#42
Elastic bands width and height:
#40 W 2.0 mm // H 0.75
#240 W 2.5 mm // H 0.60
#41 W 3.5 mm // H 0.76
#42 W 4.0 mm // H 1.25
What is ocular rigidity?
It is the change in intraocular pressure for a given change in intraocular volume. It is a measure of the elasticity of the eye.
IOP X scleral indentation.
Schiotz / Tonopen / Pneumotonometer / ORA are less accurate in eyes with scleral buckle.
Injection of gas or fluid in eyes with SB causes less elevation of IOP than normal eyes.
Eyes with SB and small intraocular bubbles have LESS / MORE increase in IOP with air travel than eyes WITHOUT SB.
Eyes with SB and small intraocular bubbles have LESS increase in IOP with air travel than eyes WITHOUT SB. The gas is more compressible.
After a SB, the corneal hysteresis INCREASES / DECREASES.
After a SB, the corneal hysteresis INCREASES.
SB and ocular blood flow.
Encircling SB decreases ocular blood flow.
Most vitreoretinal traction causing tears, tractional RD or RRD is ________.
Oblique (orthogonal vectors - 90º - or composed by radial and tangential traction).
Wich eye movement appears to be especially importante to forcing fluid through a tear?
Rotational eye movement. RDD is more common if there is vitreous traction elevating the flap of the tear.
ERM’s tend to form a _______ configuration.
Planar.
Factors that promote adhesion between the retina and the RPE.
- Viscous mucopolysaccharide betwnn the villous processes of the RPE interdigitating with the photoreceptors.
- Oncotic pressure. Proteins in the choroid cannot easily pass through the RPE and Bruch’s membrane into the subretinal space.
- Hydraulic forces. The vitreous pushes the retina against the RPE. The hydraulic forces are produced by more rapid passage of fluid from the subretinal space through the sclera than from the vitreous through the retina.
- RPE pump.
