Intraocular lens implants (IOLs) are used to replace the extracted lens as part of the standard surgical treatment for cataracts. The presence of a lens implant is known as pseudophakia (literally, "artificial lens").
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Structure
Knowledge of the structure of an intraocular lens implant is required to ensure accurate identification on cross-sectional imaging.
Generally all intraocular lens implants consist of two main elements: the optic, which is the functional lens element, and the haptics (or footplates) that hold the optic in situ. The implant is generally impervious to fluids and therefore does not enhance post-contrast administration.
The first intraocular lenses were made from polymethylmethacrylate (PMMA), an inert plastic, this has now been superseded by flexible synthetic materials, e.g. acrylic and silicone (hydrogel), such that lenses are usually now folded, allowing a smaller incision in the lens capsule, and unfolded once inside the capsule.
Multifocal lenses are now available, precluding a requirement for additional reading glasses 3.
Radiographic features
Ultrasound
On ocular ultrasound, the prosthetic lens is a hyperechoic linear/curvilinear structure lying in place of the native lens, posterior to the iris 6.
CT
The optic, the central component is visible as a thin linear hyperdensity. The haptics cannot be seen.
MRI
The optic, i.e. the central component, is visible as a thin linear hypointense structure on both T1 and T2 weighted sequences. The haptics cannot be seen.
A few of the older IOLs had platinum in their haptics which can produce a susceptibility artifact. These were generally not used after the 1980s 5.
Differential diagnosis
-
aphakia
- thick-slice images: partial voluming from the iris superior and inferior to the pupil can produce an appearance mimicking a lens implant 1
Practical points
- all intraocular lens implants are considered MRI safe up to 3 tesla 7. A study of 21 IOLs in 2012 found no significant torque of the implants in a 7 T field, nor any appreciable heating effect. Susceptibility artifacts may be seen with IOLs that contain platinum in their haptics 5.
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