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TECHNIQUE OF EYE DISSECTIONS
TECHNIQUE OF EYE DISSECTIONS
BY FREDERIC A. WOLL, Ph.D., Associate Professor, Department of Hygiene, College of the City of New York; Optometry Courses, Columbia University; Member of New York State Board of Examiners in Optometry; Honorary Member: American Optometric Association; State Societies—Alabama, California, Connecticut, Kentucky, Maine, Massachusetts, North Carolina, Rhode Island; Local Societies—Lehigh Valley Society of Optometrists, Mahoning Valley Optometrists’ Society, and Optometrists’ Club of Brooklyn . SECO
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PREFACE
PREFACE
The aim of this booklet is to present to the eye-specialist, the teacher, the student, and others interested in the study of the anatomy and physiology of the eye, some definite methods to follow in the dissection of that organ. Most dissections of the eye are not made with the same degree of care and skill used in the dissections of other organs. In following the usual method of dissecting eyes, much of the important detail is lost. Often certain membranes are confounded with others, and wrongl
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INTRODUCTION
INTRODUCTION
In eye dissections it is unnecessary to have either a large equipment of instruments or a special room. To have a laboratory at one’s disposal is but a small added convenience. Not to have it, is no serious hindrance. The work may be carried on and successfully done in one’s office or in the home, as well as in class-room or laboratory. If it is true that the atmosphere of a laboratory adds zeal to the efforts of a worker, but there is no laboratory available, then reverse the order; let the zea
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THE CANAL OF PETIT
THE CANAL OF PETIT
The canal of Petit is a “triangular space around the circumference of the lens.” That it can be “inflated through a fine blowpipe inserted through the suspensory ligament,” is the usual direction given. However, the ordinary “fine blowpipe” is much too large and too dull to be inserted through the suspensory ligament. Take a long medicine-dropper (5 or 10 cents at a drug store), or a pipette, and heat it until it is red hot over an alcohol lamp or a Bunsen burner; hold one end with one hand and
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THE POSTERIOR HALF
THE POSTERIOR HALF
The posterior half is taken first because it is the simplest and easiest of the two halves to dissect. In this half of the eye the retina may be readily seen through the vitreous; the choroid and its apparent iridescent colors through both vitreous and retina. ( Fig. 10 .) Remove the vitreous by simply tilting this half of the eye, and with the finger push out the vitreous. Fig. 10—The retina, retinal vessels, and iridescent choroid showing through the vitreous. Sometimes the vitreous will adher
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THE OPTIC NERVE
THE OPTIC NERVE
Fig. 15—Enlarged to show the entrance of the optic nerve. ( Page 48 .) The excavated posterior half may be used now to show and to study the construction of the optic nerve. In cutting the optic nerve away from the sclerotic leave at least 5 mm. of the sclerotic attached. It will make handling easier. With the thumb and forefinger of the left hand hold the nerve in such a way on the table that it will be straightened out lengthwise, and then, using the scalpel or a safety-razor blade, the latter
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THE ANTERIOR HALF
THE ANTERIOR HALF
The anterior half will show the lens in situ , the ciliary processes, the posterior aspects of the iris and the lens, the corona ciliaris, the orbicularis ciliaris, and the ora serrata. ( Fig. 16 .) If the eye has been cut in two too far forward of its equator, the ora serrata will not be present. The ciliary processes and posterior aspect of the lens may be seen to better advantage when the anterior half of the vitreous is removed. This is done with the dull-pointed tweezers, by catching hold o
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THE IRIS
THE IRIS
To see the iris, take hold of the cut edge of the choroid, and, gently pulling, separate it from its attachment to the corneo-scleral junction. The white ring on the anterior surface of this part of the second coat of the eye is the ciliary ring. With a scissors, cut around this ciliary ring at its outer edge. This specimen will show the anterior surface of the iris, and on the posterior side it will show the close relationship between the iris and the ciliary processes. A hand lens will help gr
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THE CORNEA
THE CORNEA
After the anterior portion has had everything removed from it there will be left nothing but the first coat or tunic of the eye—the anterior portion of the sclerotic and the cornea. The way the cornea seems to fit into the sclerotic is not quite as one is led to believe when told that it fits into the sclerotic much the same way in which a watch crystal fits into a watch. [3] Holding this part of the eye up to a strong light one will see that the sclerotic seems to overlap the cornea in the vert
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THE CRYSTALLINE LENS
THE CRYSTALLINE LENS
If the preceding dissections have been done, the crystalline lens will already have received some notice. To study the lens properly one should use an eye that has not been hardened and also an eye or the lens of an eye that has been in a 5 per cent. solution of formaldehyde for about two weeks. The lens in the unhardened eye will prove too friable to permit much handling. The dissection should be made, however, in order to give opportunity to notice the crystalline clearness of the lens substan
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THE CHOROID
THE CHOROID
Select an eye that has had a long part of the optic nerve left on it and place it into a 5 per cent. solution of formaldehyde. Leave it in that solution for from two to three weeks. That period of time in the fluid will be sufficient to permit the choroid to become sufficiently toughened and hardened. Leaving it in the solution longer than that length of time will not injure the eye in any way. Fig. 22—Showing how to puncture the cornea. (Page 62.) Fig. 23—Removing the cornea. ( Page 63 .) Fig.
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THE RETINA
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 n
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THE SAGITTAL OR VERTICAL SECTION OF THE EYE
THE SAGITTAL OR VERTICAL SECTION OF THE EYE
Place an eye in a 5 per cent. solution of formaldehyde for about two weeks. If the eye is kept in that solution longer than that time, the lens is apt to become so hard that in cutting it the capsule and suspensory ligament will be torn, and the lens will then become detached; if for a shorter space of time, the lens and other tissues will be so soft that all may be so badly torn or lacerated, that a perfect specimen will not be possible. It sometimes happens that in keeping a number of eyes tog
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THE PAPILLA, PUNCTA LACRIMALIA, AND NASAL DUCT
THE PAPILLA, PUNCTA LACRIMALIA, AND NASAL DUCT
The only way to dissect the lacrimal apparatus, other ocular accessories, and the extrinsic muscles, is to procure the head of some animal, preferably a calf’s head, because of its size. Any butcher will supply one for from forty to sixty cents. Have the lower jaw removed. It will make a less bulky piece of material to handle. Close to the inner canthus, on the inner side of each lid, will be found a little rounded eminence—lacrimal papilla—in the centre of which is a small opening—punctum lacri
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MEIBOMIAN GLANDS AND DUCTS
MEIBOMIAN GLANDS AND DUCTS
An examination of the eyelids will show the openings of the ducts of the meibomian glands a short distance back of the cilia. Very fine pins or needles that have been greased may be easily inserted for a short distance into the ducts, and then a dissection made along the course of the duct as outlined by the presence of the inserted pins or needles. Another way to see the glands is to slice through the ducts, with the scalpel or safety-razor blade, the entire width of either eyelid. This will se
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OPHTHALMOSCOPIC EXAMINATION
OPHTHALMOSCOPIC EXAMINATION
By practising on an enucleated eye, one may gain considerable ability in the use of the ophthalmoscope, and also learn to recognize the blood-vessels and other important parts of the retina. To do this, the eye to be examined must be very fresh, for only in this condition will the cornea and lens be sufficiently clear to permit rays of light to enter the inside of the eye. However, since the pupil is oblong in shape, and often only a narrow slit—but several millimetres in diameter—the field pres
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THE LACRIMAL DUCTS
THE LACRIMAL DUCTS
To find the lacrimal ducts, cut across the outer and inner canthi of the enucleated eye, pushing the eye forward and the lids backward. That will expose the conjunctiva of both eyelids and eye, and also show the conjunctival fornices. On the upper surface of the palpebral conjunctiva, and near the outer canthus, will be seen, upon close inspection, a number of minute openings, usually eight. These are the openings of the lacrimal ducts. Pins or straw that have been lubricated with vaseline, may
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THE LACRIMAL GLAND
THE LACRIMAL GLAND
The lacrimal gland is easily distinguished by its pink appearance. There are two parts, inferior and superior. The gland lies directly over the eye and near the outer angle of the orbit. In the enucleated eye, it will be found to lie near the outer canthus and over the eye. The gland may be easily dissected out of its position and then examined more closely. A hand lens will show the racemose construction of the gland. If the gland is cut in two, the racemose construction may be seen even better
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THE CAPSULE OF TENON
THE CAPSULE OF TENON
To dissect the capsule of Tenon, it is necessary to carefully remove the superficial fat and connective tissue. In text-books and illustrations, the capsule is usually shown as a definite sac-like membrane of considerable thickness, with all its parts well defined. The dissector will soon find that the capsule is not discerned so easily. It will be found to be the thin, semi-transparent, fibrous membrane that surrounds each muscle, as well as the “posterior two-thirds of the eye,” and is continu
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THE SUPERIOR OBLIQUE MUSCLE AND ITS PULLEY
THE SUPERIOR OBLIQUE MUSCLE AND ITS PULLEY
After the lacrimal gland has been dissected away, a beginning will have been made for cutting away the fat and the connective tissue. The first thing to do then is to locate the superior oblique muscle. Try to keep track of which part of the eye is the inner side. Having located the inner side, feel along the top for a little hard eminence. That is the pulley. Begin to dissect around the pulley, not through it, and then follow the muscle along to its origin; do not separate the muscle from its o
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THE OTHER EXTRINSIC MUSCLES
THE OTHER EXTRINSIC MUSCLES
With the dissection of Tenon’s capsule and the superior oblique muscle, the work of isolating the other extrinsic muscles will have begun. This work needs no directions except a warning to be careful not to injure the pulley of the superior oblique, and to be careful not to cut away the inferior oblique. The inferior oblique will be found to be near the “pulley.” If the dissection is not carried too close to the origin of the recti muscles, all the muscles may be kept in place. If the eye has no
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THE THREE TUNICS OF THE EYE, THE HYALOID AND ITS ATTACHMENTS
THE THREE TUNICS OF THE EYE, THE HYALOID AND ITS ATTACHMENTS
This dissection is a rather difficult one to make, and requires patience. Fig. 61—Cutting through the iris. Prepare an eye by placing it in a 5 per cent. solution of formaldehyde for about ten days to two weeks. Remove all the outside tissues. Cut away the cornea, as in the dissection for the choroid or the retina. Loosen, as far back as possible, the sclerotic from the choroid. Remove the sclerotic for about 10 mm. back of the equator of the eye. With the tweezers pick up the pupillary edge of
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