Video-Slide No 2

The Art & Science of

Pupil Dilating Devices

Dr. Suven Bhattacharjee. MS, DO, DNB, FRF.

suvenb@gmail.com

No Financial InterestPatent Pending (PCT)

For authors devicesNayan Eye Associates

Kolkata. INDIA.

Helical Loops or Notches at Corners?

Open or Closed Ring?

Hexagon or Square Shape?

Polypropylene or Nylon Material?

2.2-2.5 mm or 0.9 mm (20G) Incision?

Video-Slide No 2

Square or Hexagon ?

• For a 5 mm Capsulorhexis, an Incircle of 6 mm is required within the Regular Polygon

shaped Pupil Dilating device. (Regular Polygon: All sides & angles equal)

• A Square with an Incircle of 6 mm, lies within a 8.48 mm Circumcircle.

• A Hexagon with an Incircle of 6 mm, lies within a 6.92 mm Circumcircle.

• Smaller Hexagonal device - easier to handle – less injury to Cornea, Iris & Angle.

• Smaller Hexagonal device - less stretch & damage to sphincter – Post Op Round pupil.

6 mm

8.48 mm

3.46 mm

6.92 mm

Video-Slide No 2

Square or Hexagon ?

• Square with 6 mm side, when deformed : Max length of Diagonal = 6 x 2 = 12 mm.

• Hexagon with 3.46 mm side, deformed : Max length of Diagonal = 3.46 x 3 = 10.38 mm.

• New device invented by author is available as a Square and Hexagon.

• Square device is longer when deformed and delivered into AC through a small incision.

• Square device is also longer when deformed to engage or disengage pupillary margin.

• Hexagonal device requires two additional corners to be engaged to Pupillary margin.

• But with Notches & Flanges design (nxt slide) – Single flange tuck engages two notches.

6 mm

6 mm

6 mm

6 mm

6 mm

12 mm 10.38 mm

3.46 mm 3.46 mm

3.46 mm

Video-Slide No 2 Helical Loops or Notches at Corners?

Disadvantages of Helical loops (Malyugin) at Corners:

– Using Top View, aligning the side facing gap to receive pupillary margin – Is Difficult !!

– Biplanar structure at Corners - with upper and lower lips - Snags the incision !!

– Very small part of the Pupillary margin is engaged – Can Slip out !!

– Each Helical loop acts like a torsion & compression spring when the ring is deformed –

widening or narrowing the gap - Could crush or release the pupil margin unpredictably !!

New design by author, with Notches at corners and Flanges on sides with entire device lying in

Single plane, does not snag the incision. Device holds on to the Iris and does not get dislodged

easily.

Notches - can straighten and pass through a much smaller 0.9 mm (20G) incision

Flanges - easier to tuck than aligning gaps and pupil margin. Single Flange tuck engages two

notches

M Burger > 2.2 mm 0.9 mm

Video-Slide No 2

Polypropylene (PP) or Nylon?

Property PP Nylon SignificanceFloatability (in Water/ Aqueous)

Floats No PP tends to float and when disengaged may touch endothelium

Stiffness (Bend Recovery)

Good Excellent Nylon device regains shape better after being deformed as it passes through the incision, giving desired pupil size and shape

Flicking (springiness) Good Excellent Nylon device regains shape faster after being deformed

Stiffness in Water Excellent Fair Nylon (6 & 66) tends to soften a little by the end of the procedure. Nylon 612 absorbs less water. Removal is Easier. PP does not absorb water & does not soften.

Water Absorption Poor Fair

Heat Distortion/ Deflection Temperature

60-80 ˚C 165 - 185˚C PP can be bent and worked upon at lower temperature

Cost Cheaper Costlier A very small quantity being required to make a device, the difference is not significant.

PP & Nylon are both Thermoplastic, i.e. softening when heated and hardening when cooled, but are different in many ways.

Video-Slide No 2Open Ring

• Ends need to be wide apart as they collapse due to constricting force of Pupil• Device with 3 Flanges – collapses & is not practical , Thicker / Stiffer 4-0 Nylon required • Free ends can injure Cornea, Iris, Angle & capsule • May be inserted/ Removed through 23 G incision but 20 G preferable.

Closed Ring• Device maintains Shape • Pupil conforms to shape

of device • 5-0 Nylon • 20 G (0.9 mm) incision

Conclusion: Square/Hexagon closed ring, 5-0 nylon device, with notches & flanges, in a single plane - appears to be the best choice presently.

Closed Square Closed Hexagon