PPT describes the effects of scleral buckles on the changes in geometry of the eye in retinal detachment surgery.

1. EFFECT OF SCLERAL BUCKLES ON THE
GEOMETRY OF THE EYE
DR. ABHIJAAT CHATURVEDI
DR. SAURABH LUTHRA
DR. S.M. DAS
DR. SHWETA PARAKH
DR. VAIBHAV BHATT

2. • The scleral buckle alters the shape of the eye, depending on:-
– Type of buckling material used,
– The location,
– Tension of the scleral sutures,
– The circumferential tightening of an encircling
buckle.
• Secondary effects d/t changes in geometry of the eye:-
• Changes in the axial length of the eye,
• Induced spherical equivalent,
• Astigmatic refractive errors,
• Changes in the volume of the eye,
• Altered compliance (ocular rigidity) after scleral buckle placement.

3. AXIAL LENGTH CHANGES AFTER SCLERAL
BUCKLES
• Radial soft silicone sponges - induce little change,
• Segmental scleral buckles - hyperopic shift,
• Encircling scleral buckles - increases or decreases in AL, depending on :-
– The scleral buckle material,
– The location of the buckle,
– The height of the buckle.
• Hard silicone encircling buckles – increase in
AL,
• Occasionally, high encircling silicone buckles – decrease in AL.

4. GEOMETRY OF EYE WITH
ENCIRCLING BUCKLES
• (A) The normal spherical shape of the eye.
• (B) The spherical eye acquires the shape of a
prolate spheroid after placement of a moderately
high circumferential buckle.
• Horizontal and sagittal cross-sections of an eye
with a broad circumferential buckle at moderate
buckle heights show an ellipse.
• Coronal cross-section of an eye with a
circumferential buckle shows a circle.
• The anteroposterior axial length of the eye
increases at moderate buckle heights.

5. • (A) The normal spherical shape of the eye.
• (C) The eye acquires a dumbbell shape at
very high circumferential buckle heights.
• Coronal cross-section of an eye with a
very high circumferential buckle still
shows a circle,
• But the sagittal and horizontal
cross-sections show a
dumbbell shape.
• The axial length of the eye decreases
at very high buckle heights.

6. DUAL EFFECTS OF BUCKLES AND SUTURES
• The first effect:- circumferential shortening - increases the axial
length,
• By changing the shape of the eye from
a sphere to a prolate spheroid,
• With mild to moderate
circumferential tightening of an
encircling buckle.

7. • The second effect:-
• Invagination of the sclera,
• Around a broad encircling element with mattress sutures,
• Contributes to a decrease in the
axial length of the eye.
• The increases in AL,
• from circumferential shortening,
• predominate over decreases in AL
• from scleral invagination at low to moderate buckle heights,
• producing a shift toward myopia.

8. • The decreases in axial length,
• from scleral invagination tend to predominate,
• over increases in axial length at very high buckle heights.
• Some eyes with moderate to high circumferential buckles,
• have no net change in AL,
• When -
– circumferential shortening,
– scleral invagination precisely balance.

9. REFRACTIVE ERRORS CAUSED BY SCLERAL
BUCKLES
• Three primary types of refractive error can be induced by
scleral buckles :-
– First Type - an astigmatic error caused by changes in the corneal
curvature.
– Second Type - change in the spherical equivalent induced by changes
in AL, ACD or position of the crystalline lens.
– Third Type - higher-order aberrations that were found to be greater
when segmental scleral buckles are used rather than circumferential
buckles.

10. ASTIGMATIC ERRORS
• Mostly from placement of segmental or radial exoplants.
• Usually d/t high, anterior radial buckle.
• The indentation of a radial buckle in the anterior sclera - transmitted
to the cornea - inelasticity of both the sclera and the cornea.
• The greatest astigmatic errors - segmental buckle spans one to two
quadrants.
• Encircling circumferential buckles of uniform width – rarely any
substantial astigmatism.

11. SPHERICAL EQUIVALENT ERRORS
• Small shift towards myopia.
• Phakic eyes – Displacement of eyes anteriorly after encircling
buckle.
• The buckle height decreases - radial buckles over a period of
months,
• While buckle height does not decrease - circumferential
buckles.
• Circumferential scleral exoplants – shift towards hyperopia.

12. Changes in Axial Length and Refractive Error with Different
Scleral Buckles
Buckle Type Axial Length (mm) Refraction (diopter)
Narrow band −1.3
2-mm band, low buckle +0.44 −1.25
2-mm band, moderate buckle +1.09 −1.89
2-mm band, high buckle −0.35 +0.47
Implant + explant No net change
2-mm band +0.98
Half of a 7.5-mm sponge No net change No net change
Band ± tire +0.99 −2.75

13. CHANGE IN REFRACTIVE ERROR OVER TIME
• Tends to normalize after several months.
• Silicone bands - #40 and #240-style – stress relaxation of the
band over time.
• As elasticity of rubber band decreases with continuous
stretches – buckling effect with band also decreases with time.
• Scleral invagination with sutures – decreases with time –
scleral erosion at sites where suture enters – also decreases
buckling effect.

14. SCLERAL CHORD Vs SCLERAL ARC LENGTH
• Calipers are commonly used to measure distances for placement of scleral
sutures.
• The shortest line between two points on the spherical globe - scleral
chord length.
• The distance measured along the
curved surface of the globe between
two points is the scleral arc length.
• A caliper setting (chord length) of
8 mm corresponds to a
scleral arc length of 8.16 mm,
a 2% error.

15. EFFECTS ON INTERNAL GEOMETRY OF THE EYE
• The major variables that determine the internal geometry of
indentation induced by the scleral buckle exoplant :-
(1) shape of the buckle;
(2) composition of the buckle (silicone sponge versus hard
silicone);
(3) suture placement with respect to the dimensions of the
buckle;
(4) suture tension;
(5) distribution of tension from the suture to the buckle;
(6) intraocular pressure.

16. • An analysis of scleral indentation from a 5-mm radial silicone
sponge showed that the following factors decreased indentation:
(1) Placement of the suture bites too close or too far apart;
(2) High intraocular pressure;
(3) Short suture bites in the sclera;
(4) Loose sutures;
(5) Use of a half-thickness sponge compared with a full-thickness sponge.
• Factors that increased scleral indentation included :
(1) low intraocular pressure
(2) tight sutures.

17. • Orientation of the scleral buckle - determines the topography of
the indentation in the sclera.
• Radial buckles – advantageous in solitary HST.
• Moderate to high circumferential encircling
scleral buckles – radial folding of retina.
• Encircling buckle forces a
reduction in the normal circumference of the eye in the equatorial
meridian.

18. • Sclera & Retina – unable to shrink,
• Hence, excess retina, choroid and sclera – radial folds.

19. • Circumferential shortening - basis of the “fishmouth
phenomenon”.
• Wedge-shaped buckles and radial scleral buckles – minimize risk
of fishmouthing. (cause less circumferential shortening).
• The fishmouth
phenomenon results
when a radial fold
bisects a retinal tear.

20. • Circumferential encircling buckles are necessary in some eyes:-
– Multiple retinal breaks,
– Circumferential VR traction,
– Circumferential shortening d/t ERM,
– Broad circumferential encircling buckle is preferable – reduces
the circumference of eye,
– Allows repositioning of Retina against RPE.
– Allows the surgeon to avoid circumferential retinectomy.

21. VOLUME CHANGES IN THE EYE AFTER SCLERAL
BUCKLES
• Indentation by scleral buckle – displaces fluid in vit cavity – reduction in volume
of vit cavity.
• Estimation of the intraocular volume of an eye with a scleral buckle is important:
(1) Estimation of how much fluid must be withdrawn from the vitreous cavity or
drained from the subretinal space to permit placement of a specific scleral buckle;
(2) Injection of pharmacologic agents such as antibiotics or antimetabolites into the
vitreous, when therapeutic and toxic concentrations
must be considered;
(3) Injection of expansile gases into the vitreous.

22. • Amount of displacement – small for most buckles ( substantial
in case of broad encircling buckles).
• The volume displacement of a scleral buckle can be predicted as
a function of the following variables:
(1) The axial length of the eye = 2× internal radius;
(2) The buckle width measured anterior and/or posterior to the
equator;
(3) The buckle circumference;
(4) The buckle height.

23. • The decrease in vitreous cavity volume increases with increasing
buckle width and height for circumferential buckles.
• Scleral Buckle Vitreous Cavity Volume Displacement (mL)
• Half of 5-mm sponge 0.09–0.15
• 3×5 mm sponge 0.11–0.20
• 5-mm round sponge 0.14–0.22
• #240 style (circumferential) 0.47–0.48
• #276 style (circumferential) 1.08–1.13
• #287 style (circumferential) 1.32–1.57
• #280 style (circumferential) 1.82–1.88

24. OCULAR RIGIDITY AND CORNEAL HYSTERESIS
• Ocular rigidity (OR) – change in IOP, for a given change in IO
Volume, & is a measure of elasticity of the eye.
• OR decreases with encircling buckles – volume of vit cavity
decreases.
• Corneal Hysteresis – property which measures the elasticity of
cornea.
• In vitrectomised eyes with scleral buckle – corneal hysteresis
increases.

25. • The increase in intraocular pressure (ocular rigidity) is decreased in eyes with
an encircling scleral buckle because the volume of the vitreous cavity was
decreased with placement of a scleral buckle.
• This decrease in volume is related to changes in the shape of the eye caused by
the scleral buckle.
• As the intraocular pressure is increased by injection of saline solution or gas
into the eye, the eye becomes less elliptical and more spherical as the sutures
holding the buckle are stressed or the encircling band is stretched.
• The net effect is to decrease the buckling effect and to increase the intraocular
volume such that the intraocular pressure does not rise as rapidly as in the
normal eye.
• This effect can be better understood by considering an eye with an encircling
buckle and no invagination by scleral sutures.
• If water is injected into the eye, the encircling buckle will stretch as the eye
assumes a more spherical shape.

26. • Once the buckle has stretched so that the eye returns to its original
spherical shape (before placement of the buckle), the intraocular
pressure will increase rapidly.
• An injection of fluid or gas into an eye with a scleral buckle will
cause less elevation of intraocular pressure than injection of the
same volume into a normal eye, if all other factors are equal.
• Placement of an intraocular gas bubble into the vitreous also itself
reduces ocular rigidity because the gas in the vitreous cavity is
more compressible than the vitreous fluid it replaces.
• Eyes with reduced ocular rigidity from an intraocular gas bubble
and an encircling scleral buckle require even larger volumes of fluid
aspiration to reduce the intraocular pressure than normal eyes
with elevated intraocular pressure.

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