Saturday, July 22, 2006

Synthetic Intraocular Lenses

Intraocular lenses have a variety of shapes and sizes. The type of lens should be identified whether it is an anterior chamber or posterior chamber lens and if it is intact. Sometimes the haptics are amputated or the optic is transected. If there is attached tissue and the specimen was fixed in formalin, consideration should be given to sectioning the tissue. There may be infections in the residual lens capsule that are subclinical such as P. acnes or there may be evidence of pseudoexfoliation syndrome which may lead to displacement because of weak zonular support. The lens should be described carefully. In the images there is a 6 mm optic (number 1), two positioning holes (number 2) located in the haptics and there is attached tissue (number 3). The first image is a plate style and the one below has clear C shaped haptics. Both are 1 piece lens. The texture of the lens should be described, as silicone lenses are soft and flexible but polymethymethacrylate lens are hard and rigid. Careful observation will reveal that the lens above has fibrous tissue remaining from the residual lens and the other has iris tissue from an anterior tuck. These findings should be correlated with the clinical history to understand the reason for removal of the lens. The color of the haptics should be described for the posterior chamber style PCIOL below. This particular lens is flexible and made of silicone, which must be proven by attempting to fold the optic..

One important lens is the RESTOR lens which is recognized by its apodized diffraction rings. This is best seen with reflected back illumination. It is easily missed without careful examination. The lens should be returned to the patient for a rebate if appropriate.

Close inspection of intraocular lenses under the dissecting microscope sometimes reveals some very interesting findings. For example here is a lens that was removed after cataract surgery for displacement into the vitreous. Note the pits in the IOL follow a somewhat circular distribution (arrows 1). However, one disruption of the plastic appears to have occurred in the substance of the lens (arrow 2).

Turning the lens at a slight angle reveals that the defect is fan shaped similar to the energy burst from an exit wound. The patient has had Yag capsulotomy and frequently there are a few shots that are slightly off focus. These findings should be recorded, particularly the location of the defects to the visual axis, in this case off axis.

The anterior chamber style intraocular lens is easily recognized by the distinctive shape of the haptics. Each haptic joins the optic to form an "S" (white arrows). The anterior chamber lens is placed in the eye when a posterior chamber lens is contraindicated. The most common reason is posterior capsule rupture during cataract surgery. The remaining lens capsule and zonule are not sufficient to support the intra capsular sulcus placement of the lens. Anterior chamber intraocular lenses are generally removed because an inappropriate size was placed in the anterior chamber. The direct trauma to the posterior cornea or the iris may produce endothelial cell loss or iridocyclitis. It is important to look for any vitreous clinging to the wound.

Phakic intraocular lenses, like the Artisan lens, have become somewhat popular and their insertion is considered a cosmetic procedure. The lenses may have a modification so that the lens can rest against the iris. They are partially flexible. However, endothelial cell loss has been well documented at about 1.8%/year with these lenses. The lens may be removed after the onset of corneal edema and bullous keratopathy as in this case. The phakic intraocular lens may be recognized by their distinctive shape.



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