Technique of Eye Dissections

THE RETINA

Isolating the retina from the other tissues requires considerable patience and dexterity. When the retina has been removed and placed in a special receptacle, it will be found that the specimen is well worth the little amount of time spent in making it. Previous techniques, even the writer’s own, sometimes took nearly two hours to do, and rarely was the retina isolated without puncturing or tearing it; perfect specimens were almost impossible. The following method will assure one of success in nearly every instance. Failures are almost impossible. Punctures, perforations, tears, etc., are rare. The beginner should isolate the retina in about six to seven minutes; the expert in about four and a half to five minutes.

Select an eye with a long optic nerve, and prepare it for this dissection by placing it in a 10 per cent. solution of formaldehyde for about ten to fourteen days, but no longer. If it is left in the hardening fluid longer than that length of time, it will interfere with the easy removal of the vitreous.

Fig. 31—Cutting through the iris. (Page 77.)

Fig. 32—Showing how to cut around the ciliary ring. (Page 77.)

The first part of this dissection is the same as the beginning of the dissection for the isolation of the choroid. Remove all the outside tissues first, and then the cornea, and about 10 mm. of the sclerotic, as described in the preceding dissection. (See Figs. 22, 23, 24, and 25.) That will lay bare the iris and a few millimetres of the choroid.

Fig. 33—Lens, iris, and part of vitreous removed. (Page 78.)

After that has been done, turn the eye so the iris will be uppermost. With the tweezers pick up the pupillary margin of the iris, and with the fine-pointed scissors cut through the iris and the ciliary processes (Fig. 31); separate both from the choroid by cutting close to the posterior edge of the processes. (Fig. 32.) In doing that, cut partly through the vitreous also, but be careful not to injure the peripheral edge of the retina—ora serrata. After the iris has been separated from the choroid, cut completely through the vitreous in such a way that the lens will also be removed with the iris. (Fig. 33.)

Fig. 34—Showing how to force glass blowpipe (A) into vitreous (B). (Page 80.)

Fig. 35—Showing bulging out of vitreous caused by blowing air through glass blowpipe. (Page 80.)

Fig. 36—Showing the vitreous (A) removed.

Holding the eye suspended by its optic nerve, force the glass blowpipe through the vitreous until it all but touches the posterior part of the retina (Fig. 34); blow gently at first, increasing the pressure until the vitreous suddenly bulges outward. (Fig. 35.) If the iris has been cut away close to the ora serrata, the vitreous will not only bulge forward, but it will fall out. If, however, it does not detach itself at once, insert the scalpel close to the choroid and with its flat side press downward until a separation occurs. Do not let the vitreous drop out too suddenly, because it may tear the retina. Let the vitreous detach itself slowly by the force of its own weight, though it will be well to hold some of its weight on the scalpel. (Fig. 36.)

Fig. 37—A. Showing retina folded upon itself by blowing air at it through the glass blowpipe. (Page 83.)

Fig. 38—A. Showing folded retina suspended from its attachment, so sclerotic and choroid may be easily cut away. (Page 83.)

After the vitreous has been removed, turn the eye upward, and by blowing strongly through the blowpipe at the marginal edge of the retina, turn the retina upon itself. Repeat this until the retina lies in a small wrinkled lump at the “bottom” of the posterior part of the eye. (Fig. 37.) Invert the eye (Fig. 38) and cut away both the choroid and the sclerotic close to the optic nerve. No care need be taken in doing this until the scissors come close to the optic nerve. (Fig. 39.)

Fig. 39—Showing the sclerotic nearly all cut away.

Fig. 40—Isolated retina, with optic nerve attached.

After the choroid and the sclerotic have been cut away, drop the retina into some water, and it will slowly unfold itself by “ballooning” out into a perfect and beautiful specimen. (Fig. 40.) But, if it is desired to study the specimen closely, it is better to suspend it in a jar or bottle made of thin glass, and containing a 5 per cent. solution of formaldehyde. Remember that the retina is a delicate membrane in any state; the slightest rough handling may cause it to be torn, or otherwise damaged. If the vessel, in which the specimen has been placed and suspended, has enough preserving fluid to completely fill it, and it is firmly stoppered, the whole thing may be inverted, and turned in any direction, even abruptly, without fear of damaging the retina. This way of keeping the retina will give opportunity to inspect and study the inside as well as the outside of the membrane; the blood-vessels, and other important parts easily recognized.

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