8. Intraocular lenses

Question 1

list types of IOL designs. diagram p.2

Answer 1

anterior chamber
iris fixation
iridocapsular fixation
posterior chamber.

Question 2

optic (and loop) part of some lenses are made of? give some information regarding initial and secondary lenses.

Answer 2

most initial lenses are now of posterior chamber type. secondary lenses are of anterior chamber type.

optic part of some lenses made of PMMA. sg (specific gravity?) = 1.19, RI = 1.49.

various materials for loops e.g. nylons, polypropylene.

Question 3

list some types of posterior chamber lenses.

Answer 3

foldable silicon posterior chamber lenses.
HEMA posterior chamber lenses.

Question 4

describe the theoretical formulae of power calculations with IOLs

Answer 4

most measurements provided by instruments such as IOLMaster and Lenstar. these provide corneal power (keratometry), anterior chamber depth and axial length. for IOL master, axial length provided by PCI and anterior chamber depth by an optical method. for Lenstar and then new version of IOLMaster, both of these measurements provided by PCI.

Question 5

describe the correlation between pre- and post-operative anterior chamber depth.

Answer 5

little correlation. post operative depth depends on lens type.

Question 6

list some examples of instruments used to take required measurements for power calculations of IOLs.

Answer 6

IOLMaster and Lenstar

Question 7

what measurements are needed for power calculations of IOLs?

Answer 7

These provide corneal power
(keratometry), anterior chamber depth and axial length.

Question 8

theoretical formulae of power calculations with IOLs? (draw diagram)

Answer 8

F = n/(l – c) – nK/(n – Kc) (p.4)

Question 9

Example: An eye is to undergo cataract surgery and IOL
implantation. K 40 D, l 24 mm, c 3 mm (estimated). What is
required lens power for emmetropia?

Answer 9

F = n/(l – c) – nK/(n – Kc)
= 1.336/(0.024 – 0.003) – 1.336x40/(1.336 – 40x0.003)
= +19.67 D