Deformation of the globe under high-speed impact: Its relation to contusion injuries

F. Delori, O. Pomerantzeff, and M. S. Cox*

Enucleated pig in 10 per cent gelatin were submitted to nonperforating injury in order to record and measure the deformations of the and explain the mechanism of damage at the vitreous base. High-speed motion pictures and single flash high-speed photographs were used for this purpose. The general theory of the central impact of two bodies was correlated with previous and present experiments. Reconstruction of the motion was based on the con- stancy of the mass of the globe and on the experimental data obtained. This reconstruction was used to determine local accelerations of the ocular coats, distension of the walls, energetic balance and magnitude of the forces involved. A theory was proposed to explain the damage observed at the vitreous base.

Key words: vitreous base, photography, pigs, enucleation, mathematical analysis, eyeball contusion, capsule, , ciliaris.

D,amage to the peripheral and tography and cinematography, the very pars plana ciliaris from nonperforating rapid deformations of the globe caused by trauma of the eye often results in retinal the projectile and the mechanism by which breaks along the border of the vitreous damage was produced to the ocular tissues. base: dialysis along the posterior border and linear breaks in the epithelium of the Materials and methods pars plana ciliaris along the anterior bor- Eyes and molds. The pig eye was chosen by der.1 Weindenthal and Schepens2 dupli- Weidenthal because of its similarity to the in the area of the ora serrata and pars plana cated these breaks by traumatizing enucle- ciliaris. Pig eyes were enucleated and traumatized ated pig eyes, mounted in gelatin, with an within 2 to 4 hours after the animal's death. air rifle projectile. They demonstrated ex- Each eye was mounted in a separate gelatin perimentally that equatorial expansion of mold consisting of a 5 by 5 by 8 cm. container the globe under impact is partially respon- made with flat glass plates. The eye was suspended in the container by threads, and liquid 10 per cent sible for the damage. With Weidenthal's gelatin at a temperature of 30° to 40° C. was model we investigated, by high-speed pho- poured in the container leaving the anterior part of the eye exposed (Fig. 1). The liquid gelatin was then allowed to gel. From the Department of Retina Research, Institute In order to study the stretching of the ocular of Biological and Medical Sciences, Retina coats, fine black threads were sutured to the Foundation, Boston, Mass. and small knots made in it as reference points. This work was supported by a Public Health Changes in the length of the globe's axis were Service Research Grant B 3489 of the National measured with reference to the dimensions of the Institute of Neurological Diseases and Blind- axes before impact. ness, United States Public Health Service. Mounted in gelatin, the eyes had a pressure Manuscript submitted May 9, 1968; revised manu- varying between 15 and 20 scale readings with a Schi0tz tonometer. The normal reading in vivo script accepted July 11, 1968. was about 5 scale readings." No attempt was made * Special Fellow of the National Institute of Neuro- logical Diseases and Blindness, United States "Readings were relative on pig eyes since the Schi0tz Public Health Service (NB 1368). tonometer is designed for the human eye. 290

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1. Enucleated Eye the with the missile path. The disadvantage 2. 10% Gelatin of this type of mounting was a small deformation 3. Gun of the cornea before impact due to the air blast. 4. Contact Assembly Photographic recordings. Photographic record- 5. Glass Mold ings consisted of high-speed single flash photogra- 6. Steel BB phy and cinematography. In single flash high- 7. Magnesium Missile speed photography4 (Fig. 2), the object was illuminated during a very short time so that all motion seemed to have "stopped" on the photo- graph. The experiment took place in complete darkness. The camera, focused on the eye, was opened for one second during which the gun was fired. When the bullet left the gun, it closed momentarily a pair of electrical contacts consisting of 0.0015 inch steel blades. A resulting voltage pulse was sent through an adjustable delay line" to an electronic flash unit,f which produced a Fig. 1. Enucleated pig eye mounted in 10 per short but powerful flash of light. The exposure cent gelatin in a glass mold. The muzzle of the time was thus equal to the length of the light air rifle with its contact assembly is shown to the pulse (3 Msec), and the intensity of the flash was right. The insert illustrates the two types of mis- about 7 million beam candlepower. The light flash siles used. was intentionally produced between 0.1 and 10 msec, after the voltage pulse depending on the to normalize the intraocular pressure of the enucle- phase of motion to be photographed. The delay ated eyes. Fluid injected into the intraocular cav- was preset and measured for each exposure with ity might have escaped from the globe through the a cathode ray oscilloscope. The use of direct de- needle track during impact. Any method of in- velopment film with high sensitivity! made the creasing the pressure externally would have limited procedure very versatile. This technique would movements of the globe during impact. Since have been inefficient if only one picture per eye damage to ocular tissues, observed under these could have been taken. The deformations of the conditions, was similar to that observed when the globe under repetitive impact were so similar that globe was left in situ,1 it did not seem important no changes greater than the experimental error to normalize the pressure. could be detected. This permitted the use of the same eye for repeated impacts and photographs. Two human eyes were used which had been However, no measurements of eyes after the fifth enucleated 12 and 24 hours before the experi- impact were taken into account. Pictures of the ment. The donor" was a 24-year-old woman undistorted eye were taken before and after a whose eyes had been removed 4 hours after death series of impacts. A total of 213 single flash pic- from uremia. tures of pig eyes were taken. Missiles. The ocular injury was produced by a specially modified air riflef which fired a standard With high-speed cinematography (Fig. 3) the projectile called a BB (0.345 gr.) at an average object to be photographed was continuously illumi- speed of 62.3 M. per second (±2.5 per cent). This nated, and the film was exposed during very speed was selected to insure a nonpenetrating short times by a fast shutter. The camera^ was trauma of the cornea since it had been established driven by a motor at speeds between 5,000 and that penetrating injury occurred at speeds higher 3 9,000 frames per second. Some time was required than 72.0 M. per second. It was necessary to use before the film reached the desired speed, then a magnesium projectile, of greater length but the gun was fired by a pair of solenoids actuated identical speed and weight as the steel BB, to by an event synchronizer inside the camera. A 60 measure the depth of the corneal indentation dur- cycle per second flashing light was incorporated ing impact because this indentation was larger into the camera, and its flashing was recorded on than the diameter of the BB (0.45 cm.). The the film to permit the establishment of a time density of steel is 7.8 and that of magnesium is scale of events. 1.7 (Fig. 1). With either projectile, the same amount of kinetic energy was delivered to the eye The high-speed negative films|| used were 100 (K.E. = % mv.- = 0.68 joule). The mold con- feet long. Their relatively low sensitivity required taining the eye was rigidly mounted at a distance powerful illumination by 3, 625 watt projectors. of 2 to 3 cm. from the muzzle of the gun. This "General Electric 1531-p2. was necessary to insure alignment of the center of {General Electric 1531-A. JPolaroid Type 57 (3000 ASA black and white). "The eyes were supplied by the Boston Eye Bank. $Hycam. K1001, Red Lake Laboratories. fDaisy Manufacturing Company, Rodgers, Ark. ||Eastman Kodak Tri-X (ASA 400) and 4-X (ASA 443).

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SCOTCH LITE SCREEN

SOLENOIDS

MANUAL CONTROLS

CONTROL FOR PRESETTING TIME DELAY Fig. 2. Schematic illustration of the setup for single flash high-speed photography.

SCREEN ILLUMINATION

DIFFUSING SCREEN

DIRECT l» ILLUMINATION CONTROL NEON TIME MARKER P.S.

CONTROL -FOR FILM SPEED a FUSE

Fig. 3. Schematic illustration of the setup for high-speed cinematography.

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This method was more informative than the single flash procedure since the complete event was re- corded in one film strip. The picture quality, how- ever, was inferior because of the lower sensitivity of the film and the longer exposure time (50 to 70 fisec instead of 3 /isec). Ten high-speed movies were taken of pig eyes and 2 of human eyes. Other methods. Static indentation of the globe was performed with a known force by cylinder having a hemispherical end of the same diameter of the BB projectile (0.45 cm.). The resulting strain of the anteroposterior diameter was mea- sured for each load. The impact of a BB projectile was also applied on a rubber sphere filled with water. The sphere had an inside diameter of 25 mm. and a thickness of 1.7 mm. The deformations of the rubber sphere

Fig. 4. Series ot 5 single flash photographs taken Fig. 5. Single flash photographs illustrating the before impact, 0.05 msec, after impact, 0.30 msec, long missile 1 Msec before and 25 msec, after im- after impact, 0.80 msec, after impact, and 1.50 pact. msec, after impact.

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-20

0.2 0.4 0.6 0.8 1.0 Time-milliseconds Fig. 6. Graphic illustration of the deformations of the eye during the first 1.9 msec. Ordinate: dimensions of the eye expressed as percentages of their original value. Abscissa: time after impact in milliseconds. A cross section of one half of the eye before impact is reproduced on extreme left on ordinate (shaded area). The posterior pole is on the 0 point of the ordinate and the anterior pole on the 100 point.

were recorded by a single flash technique. The were examined with the aid of a dissecting sphere was mounted in air and attached by its microscope a few days after fixation. The posterior pole to a rigid wall. The existence of a damage was qualitatively the same as that shockwave was investigated by placing a small observed by Weidenthal and Schepens,2 crystal pressure detector" at the posterior pole of the rubber ball and recording its electrical signal but the percentage of damaged eyes was with an oscilloscope. smaller. Lower ocular pressure before the experiment and lower missile speed (62.3 Results M. per second instead of 65.4 M. per sec- Seventy-five pig eyes were traumatized ond) may account for the difference. in the center of the cornea. Most experi- Interpretation of the photographic re- ments recorded deformations of the sagittal cordings. The anteroposterior and equa- plane. The structure of the ocular coats in torial diameters of the eye were measured the pig gave no indication that relative during deformation and' expressed as a deformations would lack symmetry around percentage of their original value. Results the axis of the eye. Nevertheless, a few are presented in a graph (Fig. 6) as a experiments were performed to investigate function of time after impact. There was the deformation of the equatorial plane. an error in measurement of the antero- Figs. 4 and 5 show examples of the recorded posterior diameter caused by the different single flash pictures and frames of the high- refractive indices, one part of the globe speed movie films. Thirty eyes traumatized being in the air and the other in gelatin. by single impact were placed in formalin This error was minimized by the fact that fixative immediately after trauma. They the angle subtended by the eye at the camera objective was small (4 degrees). Measurements of equatorial diameters were °Valpey Crystal Corporation.

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made in pictures of the posterior pole* and move posteriorly until the eye assumes a showed no significant differences between pear shape around 1.0 msec. At the same the relative deformations of the apparent time the bullet leaves the eye with an horizontal and vertical diameters. average speed of 11.4 M. per second, 5.4 The movement of the posterior pole was times less than the impacting speed. measured with reference to a fixed point Analysis of the recordings for this period in the mold and was expressed as a per- of time shows a deformation wave travel- centage of the original anteroposterior di- ing posteriorly on the sclera. This wave ameter. Measurements of the distance be- originates most probably at the limbus tween the apparent equator and the pos- where it is generated by the sudden radial terior pole were also expressed as a outward movement of the aqueous pro- percentage of the original anteroposterior duced by the indentation. This phenome- diameter. The long oscillations of the eye non does not appear distinctly on all re- in gelatin were measured with a frame by cordings but seems to be favored by a low frame analysis of two high-speed films. ocular pressure which corresponds to a Measurements of the anteroposterior and low tension in the ocular coats. equatorial diameters of the 2 human eyes During this period the whole globe showed similar results. The complete phe- starts to move backward. No explanation nomenon of the impact on the cornea could can be given for the small irregularity in be divided into the following periods: com- the curve showing the position of the pression, decompression, overshooting, and posterior pole versus time (around 0.70 long-time oscillations. msec, in Fig. 6). This cannot be due to a Compression (between 0 and 0.25 msec). "shockwave" traveling through the vitreous The cornea does not present a marked and applying a force on the posterior pole. resistance to the impacting bullet. Even In order to travel through the globe in the blast of the gun causes a small de- 0.70 msec, its speed should be between 24 formation before impact. A rapid expan- and 28 M. per second and a shockwave in sion of the anterior sclera compensates for water travels at 1,500 M. per second. the volume decrease caused by the corneal Overshooting (between 1.0 and 2.5 indentation. The BB is stopped after about msec). The anteroposterior diameter over- 0.25 msec, by the transient gradient of shoots up to 112 per cent of its original pressure developed by inertia of the tissues length, whereas the equatorial diameter and liquids accelerated by the bullet, and decreases, giving the globe an ellipsoid by the tension in the cornea. At this shape. It is clearly visible on the readings moment, the globe's anteroposterior diam- that the whole globe moves back as it re- eter is reduced to 59 per cent of its original covers its normal 100 per cent anteroposte- length, which corresponds to a corneal in- rior diameter at about 1.15 msec. dentation of 8.5 mm. It is probable that Oscillations (from 2.5 to 100 msec). during this period the posterior surface of Curve No. 3, Fig. 7 represents the oscilla- the cornea comes in contact with the an- tion of the posterior pole, which may be terior surface of the lens. considered as the oscillation of the whole Decompression (between 0.25 and 1.00 globe. Its frequency was estimated at 85 msec). The eye acts as a tension spring cycles per second. In addition to this oscil- and pushes the bullet out. The equatorial lation, the fluids inside the eye oscillated, diameters continue their expansion until expanding periodically in the anteroposte- 0.40 msec, when they reach their greatest rior and equatorial directions, and this sec- values, 128 per cent of their original length. ond oscillation is represented in curves No. Simultaneously the starts to 1 and No. 4. In these curves, the maximum anteroposterior elongation corresponds ap- °With the use of a 45 degree mirror so that the camera was not located in the axis of the gun. proximately to the minimum equatorial di-

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^•VARIATION OF EQUATORIAL DIAMETER

___ ANTERIOR r^ POLE #2

LENGTH OF A-P" OIAMETER

1 !POSTERIOR POLE #3

/-VARIATION OF A-P DIAMETER __ POSTERIOR T POLE #4 TIME DURING WHICH , THE BB IS IN CONTACT WITH THE EYE LENGTH OF A-P DIAMETER I I I I I 1 10 20 30 40 50 60 70 80 90 100 110 Time-milliseconds Fig. 7. Graphic illustration of the change of the dimensions and position of the eye during the first 100 msec. Abscissa: time from impact in milliseconds. Ordinate: percentage of original equatorial or anteroposterior diameter, original diameter being equal to 100. Original position of posterior pole is at 0 and of anterior pole at 100. The changes represented in Fig. 8 are not reproduced here because of the different time scale.

PHASE I

.00 .05 .10 .15 .25 Milliseconds

Scale - x 6.66

PHASE 2

1.00 .80 .60 .40 .25 Milliseconds Fig. 8. Graphic reconstruction of the changes in shape of the eye based upon a constant volume assumption. The shaded area represents the impacting BB. Phase 1: millisecond from the time of impact to 0.25 msec. Phase 2: millisecond from 0.25 msec. to. 1.00 msec.

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ameter. The frequency of this oscillation is eye by forced diffusion through its walls. about 90 cycles per second. The oscillation The constant volume assumption was used in gelatin (curve No. 3) stops after 50 to determine shapes that were not visible msec, whereas the corneal oscillation is on the recordings. Fig. 8 shows the results fully attenuated by 100 msec, (curves No. obtained, all volumes being computed 2 and No. 4). Similar movements of the within 2 per cent of the original volume eye fluids were found by Tillett, Rose, and 3 of 6.88 c.c. by graphical integration. A Herget in their study of perforating injury schematic representation of the changes with a BB. in shape is illustrated in Fig. 9. With the Graphic reconstruction. These experi- help of this reconstruction it was possible mental data and further analysis of the to compute the relative length of the 12 shape of the eye after impact made it pos- o'clock meridian and the relative surface of sible to reconstruct graphically the phe- the globe (Fig. 10). Elongations as high nomena resulting from the impact. Average as 5 per cent were observed in the cornea dimensions, derived from measurement of and 3 per cent in the sclera at the equator. 10 nontraumatized pig eyes after fixation, Static indentation. The stress-strain rela- were used as original values (100 per cent) tion of the anteroposterior diameter of the in this reconstruction. The volume of the eye when indented by a 0.45 cm. diameter globe was assumed to remain constant dur- hemispheric surface is shown on Fig. 11 ing its deformation. This assumption rests which represents the average of 4 measure- on the fact that during the whole event ments. Rupture of the cornea at the site of (about 100 msec.) no fluid could leave the loading occurred with a load of approxi- mately 11 kg.

6 i_ Discussion Kinematics and dynamics of a central9 • I 1 impact on the eye. When a body having a -0.2 V^ 08 \J mass M and a velocity V collides with a body at rest and having a mass M' it can be demonstrated that the energy T lost by /I the incident body during the impact is 0.0 \^ i.o V-' equal to:

8 ^^mm\ r\ Af 1 v 1 or 2 2 2 0.2 Y '•2 fi T = y2 MV - y2 M'v0 - y2 MV (2) 9 |i where Vo = speed of M' after impact; V = • ( 1 speed of M after impact; g = coefficient 1.4 ps depending on the elastic properties of both 0.4 Y bodies, g is often called coefficient of resti- 5 IO 1L tution since it is a measure of the energy k\ loss. It is defined by: * v 1 0.6 \J g 3 i.6 r^ —— < ) Fig. 9. Simulated filmstrip illustration made by When g = 0, the impact is said to be using the computed changes in shape of the eye based upon a constant volume assumption. Time plastic and the 2 colliding bodies remain in is noted in lower left corner, in milliseconds. contact after impact. When g = 1, the (Magnification xl.33.) "The velocities of the centers of both \>P$iqz nre coUnear.

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106 2000 105 MERIDIAN 104 BULLET LEAVES 1800 103 THE EYE 102 1600 101 100 .2\ .4 .6 1400 99 MILLISECONDS 98 \ / 1200 97 \ \ /••—SURFACE 96 1000 95 MAXIMUM 94 h- INDENTATION OF BULLET 800

Fig. 10. Graphic illustration of the computed 600 changes in length of the 12 o'clock meridian (top curve) and surface of the globe (bottom curve). Abscissa: time in milliseconds. Ordinate: percent- 400 age of original length or surface. 200 impact is said to be perfectly elastic and there is no loss of energy. If E is the kinetic energy of the impact- 100 90 70 60 50 ing body, equation 1 becomes: Fig. 11. Graphic illustration of the stress-strain characteristics of the anteroposterior diameter of the eye subjected to axial loading. Abscissa: per- centage of original anteroposterior diameter. Ordi- nate: load in grams applied to a 0.45 cm. hemi- E ' spheric surface placed on the center of the cornea. A graphic representation of this equation for various values of g is given in Fig. 12. It shows clearly that for the same kinetic speed. They observed no damage to the energy of the impacting body the absorbed eye in the latter case. energy decreases with the speed. It is pos- The bullet, after impacting the eye with tulated that a certain damage is produced a speed of 62.3 M. per second (0.669 Kg.- to the tissue by a certain amount of ab- M.), was pushed out at a speed of 11.4 M. sorbed energy. This means that for a given per second (0.0224 Kg.-M.). Thus 96.7 per kinetic energy, speed is the factor produc- cent of the impacting energy was used by ing the damage. In other words, to produce the system and dissipated in free oscilla- equivalent damage, less energy is required tions, heat absorption due to friction, and with high speed and small mass missiles damage to the structures of the eye. than with low speed and large mass mis- Since the movement of the anterior pole siles. of the eye was the same as that of the Available experimental evidence fits the bullet (mass: 0.345 gr.) during impact, it curves of Fig. 12. Weidenthal and Sche- was possible to estimate the force applied pens2 made experiments with a relative to the eye by the bullet. A graphic integra- tion of this movement in Fig. 13 shows a M mass, — of 0.079 with high speed and maximum acceleration of the center of the M' cornea (80 x 10 M. per second per sec- with a relative mass of 51.33 with low ond) around 0.15 msec.

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WEIDENTHAL S SCHEPENS AND PRESENT STUDY -M/M'=.O79

.g = 0 (PLASTIC)

WEIDENTHAL a SCHEPENS M/M' = 51.33

0.05 0.1 50 100

Fig. 12. Graphic representation of the relation between absorbed energy T and relative mass of impacting bodies r-rM . The body in motion has a mass M and kinetic energy E; the body at rest has a mass M'. Abscissa: relative mass —M. Ordinate: loss of energy expressed in per- T centage of total kinetic energy (percentage of-p). Curves were made for various values of the coefficient of restitution g. The point representing experimental conditions studied by Weidenthal and Schepens, and by the present study are noted on the chart.

DISPLACEMENT OF CORNEAL CENTER SPEED OF CORNEAL CENTER

Fig. 13. Graphic representation of the displacement (x), speed (v), and acceleration (y). Dis- placement (x, thin line), speed (v, thick line), and acceleration (y, dashed line) of the anterior pole of the eye. Abscissa: time after impact, in milliseconds. Each number on the ordinate must be multiplied by 1(H vm. for x; by 103 ^- for v; and by 107 -^k; for y. SCO. SGC«"

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BULLET LEAVES AIRBLAST THE EYE •ANTERIOR POLE ANTERIOR

O.IO 0.30 0.50 0.70 0.90 1.10 1.30 1.70 1.90 Time-milliseconds

Fig. 14. Graphic representation of the deformation of eye structures and of the elongation of the vitreous base. A meridional section through the eye, at the time of impact, is repre- sented at the left. The same section is represented at the right 2 msec, after impact. Abscissa: time in milliseconds. Ordinate: relative deformation of eye structures. Line D shows the elongation of the vitreous base during impact.

The corresponding force F is (action = pushed anteriorly, because of the forced reaction) mass movement caused by wall deforma- F = M Y = 276 newtons (28 Kg. tion. The same theory, called the return- force) (5) shock theory, was mentioned by Frenkel5 where M is the mass of the bullet (0.345 to explain rupture of the zonules as a re- gr.) and Y the acceleration. The graph in sult of blunt trauma. Our experiments, Fig. 13 assumes a central impact, with an however, do not support this view. When acceleration which is always normal to the the lens was pushed anteriorly (between cornea and no tangential acceleration. 0.70 and 2.5 msec.) the anterior part of the Similar computations were performed to eye was relatively contracted because the investigate the acceleration of different fluid had accumulated in the posterior seg- points of the eye. Both tangential and nor- ment. At that moment the vitreous base was mal accelerations of the sclera were found not tugging on the and retina. In to be greatest in the area corresponding to fact, distance measurements computed from the zone of damage to intraocular struc- the recorded shape of the eye, at that stage, tures. The meridional distension of the even show that the vitreous base was prob- sclera was also maximal in this area. This ably in a relaxed state during this period. would cause sheering forces between the Because of the viscosity and inertia of ocular coats if their moduli of elasticity the fluids in the ocular cavity it is pos- were different. sible that negative pressures could be re- sponsible for some of the damage. Along Theory explaining the damage observed. this line a theory of formation and sudden It was initially thought that damage at the collapse of cavities has been propounded vitreous base occurred when the lens was to explain brain damage by an impact on

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Table I. Deformation of the globe under between vitreous base and posterior pole high-speed impact of the lens is increased. The variation of this distance during the total event was Variations of the distance: Posterior pole of the lens—vitreous base computed graphically (Fig. 14). It turns out that at 0.40 msec, the above mentioned Percentage of distance Time (msec.) before impact distance is greatest with 128 per cent of its 0.00 100 initial value (Table I). At that time, the 0.05 105 intraocular pressure, in the area of the 0.10 111 vitreous base, is markedly increased and 0.15 118 0.25 125 exerts a force in a direction which is op- 0.40 128 posite to that of traction on the base. As 0.60 107 the zonule and lens capsule are distensible, 0.80 94 1.00 87 traction on the suspensory ligament and 1.20 89 the lens itself causes less damage than 1.40 94 traction acting directly on the vitreous base 1.60 94 which is less distensible. 1.80 94 The greatest shearing forces in the ret- ina are located along the posterior border the skull.0 This theory, however, assumes of the vitreous base, which explains why the existence of a shockwave, and no shock- damage occurred frequently in this region. wave was observed in our experiments. The retina is pushed against the choroid Measurements taken with a rubber sphere by increased intraocular pressure, but this indicate that if a shockwave were present, force is overcome by the strong pull ex- it would occur within a matter of micro- erted on the vitreous base. These conditions seconds after impact and it could not be are aggravated by the fact that the ocular the cause of a marked deformation of the coats, including the retina, are distended ocular coats which occur around 0.4 msec, during that particular phase of the impact. after impact. The fact that the most rapid and extensive deformations of the anterior The authors acknowledge the advice of Professor H. Edgerton (Laboratory for High Speed Photog- segment of the sclera occur in the initial raphy, Massachusetts Institute of Technology) and phases of the impact (between 0 and 0.60 Professor C. A. Berg (Laboratory for Fluid Me- msec.) suggests that the cause of the dam- chanics, Massachusetts Institute of Technology). age should be looked for during this period. The greatest traction on the vitreous base REFERENCES occurred around 0.40 msec. The damage at 1. Cox, M. S., Schepens, C. L., and H. MacKenzie the vitreous base reported by Weidenthal Freeman: due to ocular and Schepens- and observed in this study contusion, Arch. Ophth. 76: 678, 1966. strongly indicates severe traction on the 2. Weidenthal, D. T., and Schepens, C. L.: Pe- ripheral changes associated with ocular vitreous base following impact. The vitre- injury, Am. J. Ophth. 62: 465, 1966. ous body is firmly attached to the retina 3. Tillett, C. W., Rose, H. W., and Herget, C: and epithelium of the pars plana ciliaris High-speed photographic study of perforating in the region of the ora serrata and to the ocular injury by the BB, Am. J. Ophth. 54: posterior lens capsule. Between 0 and 0.40 675, 1962. msec, after impact the lens is pushed pos- 4. General Radio Company: Handbook for high speed photography, with a foreword by Dr. teriorly at the same time as the envelope Harold Edgerton, 1963. of the globe overlying the vitreous base is 5. Frenkel, H.: Etude sur le syndrome trauma- pushed in a centrifugal direction. It is at tique du segment anterieur de l'oeil, Ann. 0.40 msec, after impact that the perimeter Oculist 155: 78, 1918. of this part of the globe is largest (Fig. 6. Ward, J. W., Montgomery, L. H., and Clark, S. L.: A mechanism of concussion: A theory, 8). At that time, therefore, the distance Science 107: 349, 1948.

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