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.


Glaucoma valvular devices

The filtration devices are equipped with a tube (at the top of the photo) that protrudes from a base plate (white in the photo) with holes.
The device in the image is a Baerveldt implant. The description should be accurate and any obstruction of the tube should be noted. If there is unusual or exuberant soft tissue on part of the valve it should be submitted for sectioning.

Ahmed valves are clear plastic devices that contain a membrane type valve composed of 2 flaps that seal an opening. In the figure below an Ahmed valve is photographed face on or from above. In the overview, five holes lie at the periphery of the valve for positioning with suture and the trapezoidal valvular mechanism. The tube (missing in this picture would be at the base of the arrow and the direction of flow would follow the arrow. The inner workings of the valve are seen after longitudinally making a cross section of the trapezoidal chamber (in the plane of the red arrow). The aqueous flows from right to left in the blue colored channel (arrow 1). The leaves of the valve are relatively long and indicated by number 2. When the pressure in the anterior chamber is high, the valve leaves separate creating an open valve as depicted. When the pressure is low the leaves of the membrane have natural elasticity that keeps them together seen in the photograph below (valve closed arrow 3). It is important to examine the region of the valve carefully in case of Ahmed valve failure for evidence of fibrous tissue or obstruction of the valve.

An express shunt is a considerably more simple glaucoma filtration device. Click here.


Thursday, July 06, 2006

Extraocular Muscle

Rectus Muscle for ID only
How do you examine rectus muscles?
Rectus muscles receive a gross description after viewing under the dissecting microscope. The high magnification under the dissecting microscope is of the same order of magnitude (usually greater) than the low magnification at the compound microscope. During the gross examination the resident should try to identify tendon which is white and usually quite abundant with striations that run parallel to the apparent short axis (yellow arrow 2 in the figure above ). Muscle appears tan and is usually most abundant at one edge (white arrows above and arrowhead 2 in the figures). The length of the muscle removed needs to be documented accurately. Since the extraocular muscle is quite wide in vivo (about 9 mm) but the length resected quite small (usually 2-4 mm), the width that the pathologist sees in the gross is really the length of the muscle. This is especially evident when one sees the striations running in the short axis of the specimen. In the figure striations are obvious both in muscle and tendon (arrows 1 and 2) and therefore the muscle length is actually the distance between the arrowheads marked 3. In the body the long axis of the muscle is oriented parallel to arrow 3. An accurate measurement has ramifications medico-legally if the patient is under or overcorrected. So be careful!

How do you write up the gross description of an extraocular muscle?
Gross description:
Specimen 1, in formalin, labeled "right lateral rectus muscle" consists of one rectangular red and white fragment measuring 9 x 2 x 2mm in greatest dimensions. Under the dissecting microscope the external surface has fibrous white strands which are parallel and longitudinally oriented, adipose tissue, and blood vessels.
FINAL DIAGNOSIS: Muscle and fibrous tissue, "right lateral rectus muscle" (resection) - consistent with muscle and tendon

Very often a short length of muscle tendon is removed at its scleral insertion. Knowledge of the lengths of the extraocular muscle tendons is essential to determining whether it is likely that there is any muscle in the specimen at all. The medial rectus tendon is only about 3.8 mm in length and the lateral rectus tendon can be about 8 mm in length (see link for others). Without any muscle tissue the diagnosis would read:
FINAL DIAGNOSIS: Fibrous tissue, "right lateral rectus muscle" (resection) - consistent with tendon

When should you send an extraocular muscle for microscopic sections? Extraocular muscle may be sent for sectioning whenever it is necessary for the diagnosis. For example if a "slipped" muscle is suspected the surgeon wants to muscle or tendon versus a fibrotic pseudotendon. In this case microscopic sections are mandatory and a trichrome stain will highlight muscle fibers in red and collagen fibers (fibrosis and tendon in blue). Tendon appears as a compact lamellar array of fibers oriented in parallel.

Another example of an extraocular muscle that should be sent for sectioning is in cases of suspected chronic progressive external ophthalmoplegia. Here frozen sections for muscle enzymes, immunohistochemistry stains done in panels for specific proteins, and electron microscopy are necessary for the diagnosis. The surgeon needs to be wary of the needs of the pathologist to make the diagnosis, lest information will be lost without the proper fixation. The infamous ragged red fiber of CPEO is often not diagnosable in a specimen largely composed of tendon. A notable lawsuit was awarded against the surgeon that dumped a muscle biopsy into formalin in a patient with a suspected muscle dystrophy.

There are many other example when microscopy may be needed. Graves ophthalmopathy is associated with muscle enlargement, chronic inflammation, and Alcian blue mucopolysaccharide deposition.