- Email: [email protected]
A Study of 1,000 Cataract Extractions
649
E V I S C E R A T I O N
REFERENCES
1. Berens, C.: Synthetic plastic material for implantation into orbit. Am. J. Ophth., 24:550 (May) 1941. 2. Berens, C, and Rosa, F. A.: Evisceration with plastic intrascleral implants. Am. J. Ophth., 36:356 (Mar.) 1953. 3. Ruedemann, A. D.: Evisceration with retention of the cornea. Tr. Am. Ophth. Soc, 1956. 4. Poulard, Α.: Insertion sclerale de spheres et ovoids solides. Ann. ocul., 173:120, 1936. 5. King, J. H., Jr.: Personal communication, June, 1956. 6. Hughes, W. L.: Integrated implants and artificial eyes for use after enucleation and evisceration. Am. J. Ophth, 31:303 (Mar.) 1948. 7. deSchweinitz, G. E.: The comparative value of implants and the operation which has been substituted for it. Compt rend. Sect, opht., Internat. Med. Cong., Paris, 19(X), pp. 39-56. 8. Gifford, H.: On sympathetic ophthalmia after evisceration and Mules operation. Ophth. Ree, 17:584, 1908. 9. Guyton, J. S.: Enucleation and allied procedures: A review and description of a new operation. Tr. Am. Ophth. Soc, 1948, v. 46. 10. Gat, von L.: Ultraseptyl-Einstreuung in Eviszerationsstumpfe. Ophthalmologica, 117:343 (June) 1949. 11. Summerskill, W. H.: Modifications and defense of the scleral implant. Brit. J. Ophth., 37:415, 1953. 12. Berens, C.: An illimiinated retractor for eye operations. Am. J. Ophth., 27:281 (Mar.) 1944. 13. : A plastic compressor for enucleation and evisceration. J.A.M.A., 149:1316 (Aug.) 1952. A
STUDY
O F 1,000 C A T A R A C T
EXTRACTIONS
N . E . CHRISTY, M . D . Taxila,
I n some countries, Pakistan, India, and several countries in Africa, for example, there are remarkable opportunities and need for ophthalmic surgery. I n some cases this surgery must be performed under conditions w^hich by American standards might be con sidered somewhat primitive but still, in many instances, quite satisfactory results are ob tained. The present report of a series of cataract extractions performed in a mission hospital in Pakistan is presented ( 1 ) t o acquaint American readers with the opportunities for ophthalmic surgery in some other countries ( 2 ) to present a comparison of the incidence of complications during and following cata ract extraction by the intracapsular method and by the capsulotomy o r so-called extra capsular method, and ( 3 ) to report the inci dence of complications following cataract ex traction without the use of sutures. Since present-day training of residents in ophthalmology in the United States stresses the use of intracapsular methods with the use of corneoscleral o r some other type of suture, it was felt that the data presented
Pakistan
in this report might be of interest for pur poses of comparison. T h e 1,000 cataract extractions reported in this article were performed during a sevenmonth period, September, 1955, t o March, 1956, in the American Mission Hospital, Taxila, Pakistan. T h e patients were mostly Pakistani village farmers some of whom had very little conception of cleanliness o r sterility and little idea of what was expected of them in a hospital. Most of the opera tions (935 cases) were performed by one surgeon. In this hospital patients are seen for the first time in an afternoon out-patient clinic and those having cataracts o r other condi tions requiring surgery a r e admitted. A urinalysis is performed; the patient's lids and face are cleaned; and a sterile pad is applied t o the eye t o be operated upon. Phenobarbital (1.5 gr.) is given the night before operation. O n the morning of operation each patient is given phenobarbital (3.0 g r . ) and chlorpromazine (25 m g . ) . T h e patients walk t o the operating room where the pad is re-
650
Ν. Ε. TABLE TYPES
OF
Type of cataract Immature Mature senile Intumescent Hypermature Morgagnian Juvenile Traumatic Complicated
I
CATARACT
Number 54 755 40 102 9 12 11 40
moved and examined. Those having exces sive or purulent discharge have their opera tions postponed and are started on an anti biotic. Pontocaine is used for topical anesthesia and the tension is measured. A Van Lint block is administered by a nurse and a retro bulbar injection of 2.0-percent procaine with hyaluronidase is administered by the sur geon. The lids are scrubbed with a 1:5,000 Zephiran solution, a speculum is inserted, and the conjunctival sac flushed with 1:5,000 Zephiran. The incision is made with a von Graefe knife through the apparent corneo-scleral junction in the upper one half of the cornea. A s the knife emerges superiorly it is ro tated slightly so as to be more tangent to the globe. The incision is carried on u p under the conjunctiva leaving an intact bridge con junctiva 2.0 to 3.0 mm. wide and 6.0 to 8.0 mm. long. A basal iridectomy is performed in the 12-o'clock meridian. The lens is then removed either extracapsularly after a capsulotomy has been performed or intracapsularly. F o r the extracapsular extraction, the superior lip of the wound is depressed with a lens loop and the lens expressed by pres sure applied below with a muscle hook. F o r the intracapsular extraction, the conjunctival bridge is elevated with a muscle hook and the capsule forceps or erisophake is applied to the lens under direct vision and the lens slid out under the bridge. T h e iris pillars are replaced as necessary and sterile sulfamezathine (or sulfanilamide) powder and peni cillin ointment (25,000 units per cc.) are placed in the eye and both eyes bandaged.
CHRISTY
Sutures are used only in selected cases— unusually unco-operative patients, mentally disturbed patients, those having chronic coughs which could not be adequately con trolled, asthmatics, or those who feel for some reason that they cannot lie flat in bed. In this series of 1,000 operations sutures were used in only 37 cases. T h e patients are carried back to their beds and are kept in bed for eight days. T h e eye is dressed every other day and the unoper ated left uncovered after the first dressing. In some cases both eyes are operated upon on the same day. On a busy morning 40, 50, or 60 cataract operations may be performed. Patients are generally discharged on the ninth postoperative day. Those wishing glasses are advised to return to the hospital in one month for refraction. Although exact statistics concerning the incidence of cataracts in Pakistan are not available, a suggestion of the incidence may be obtained from the fact that during the period in which these 1,000 cataract opera tions were performed 6,000 patients were seen in our eye out-patient department, roughly one cataract for every six patients coming to the hospital with eye complaints. It should be noted however that most of our patients are illiterate so a relatively small percentage of the patients come because of refractive errors. The distribution of cataract types is shown by the data in Table 1. TABLE
2
T Y P E OF OPERATION
PERFORMED
Capsulotomy 365 with capsulectomy 96 Intracapsular extraction 610 Lens forceps applied above middle of lens and lens slid out under intact conjunctival bridge 524 Lens forceps applied below middle of lens and lens tumbled 41 Erisophake extraction 34 Lens forceps applied above middle of lens and zonule stripped 3 Smith extraction, pressure only 8 Burst capsules in all types of intra capsular extractions 50 Vectis delivery- with lens loop Linear extraction
33 12
ONE THOUSAND CATARACT EXTRACTIONS
651
TABLE 3 INCIDENCE OF COMPUCATIONS AND VISUAL RESULTS
All Operations 1,000 Cases
Capsulo tomy 365 Cases
Capsulotomy with Capsulectomy 96 Cases
Intracapsular Extraction 610 Cases
Complication
No.
Percent
No.
Percent
No.
Percent
No.
Percent
Vitreous loss one plus two plus three plus •Total
22 11 4
2.2 1.1 0.4 3.7
11 5 2
3.0 1.3 0.5 4.8
•1 2 0
1.0 2.0
8 5 0
1.3 0.8
317 79 9
31.7 7.9 0.9 40.5
95 22 5
26.0 6.0 1.3 33.3
34 3 1
35.0 3.0 1.0 39.0
218 55 4
35.8 9.0 0.6 45.4
tDelayed formation of anterior chamber
70
7.0
13
3.6
7
7.0
57
9.3
jNonformation of an terior chamber
8
0.8
2
0.5
2
2.0
5
0.8
SO 16 4
5.0 1.6 0.4 7.0
47 14 3
12.8 4.0 0.8 17.6
7 2 2
7.0 2.0 2.0 11.0
2 3 0
0.3 O.S
2.0 2.0
5 6 0 0 5 3 0
0.8 1.0
Striate keratitis/ one plus two plus three plus Total
Cortex in AC one plus two plus three plus Total
3.0
—-
2.1
0.8
Capsule visible in an terior chamber Iris prolapse Infection Choroidal hemorrhage Conjunctival edema Needling required Bulging wound Secondary suture of wound required SU-shaped pupil Boat-shaped pupil
82 13 2 1 8 18 8
8.2 1.3 0.2 0.1 0.8 1.8 0.8
77 7 2 1 3 14 4
21.0 1.9 0.5 0.3 0.8 3.8 1.1
2 2 0 0 0 0 0
6 150 5
0.6 15.0 0.5
2 51 2
0.6 13.9 O.S
0 14 0
14.5
3 98 3
O.S 16.1 0.5
irVision (of 912 cases) VG vision CF vision Η Μ vision LP only
841 46 19 6
91.9 5.0 2.1 0.7
295 29 13 1
87.3 8.1 3.6 0.3
82 7 6 1
91.1 7.0 6.0 1.0
537 16 6 6
93.4 2.6 1.0 1.0
.
.
0.8 0.5
* Of the 33 cases in which the lens was delivered with the lens loop, vitreous was lost in 11 cases. t Delayed formation of anterior chamber indicates the anterior chamber was not formed at the first dressing but reformed (with only atropine drops) during the first nine postoperative days. t Nonformation of anterior chamber indicates that the anterior chaml)er was not formed at the end of nine postoperative days. S Anythmg other than a keyhole-shaped pupil was considered a complication. 1! Unfortunately a visual result is not recorded for every case, in some cases through neglect and in other cases because the patient having discovered that he was able to see satisfactorily left the hospital of his own accord without waiting for further examinations or for discharge. Actual testing of postoperative visual results is in many cases difiicult since 80 to 90 percent of the patients are illiterate. Consequently a rough classification of postoperative vision has been established with four classes of visual results:—• VG stands for "vision good" and indicates that the patient counts fingers at three to four feet with no doubt nor hesitation on the ninth postoperative day; CF stands for "countsfingers"and indicates that the patient counts fingers at three to four feet but with some effort or hesitation; Η Μ indicates that the patient sees only hand movements; and LP indicates light perception only.
Ν. Ε. CHRISTY
652
The types of operation performed are shown in Table 2. Table 3 compares the incidence of compli cations and the visual results obtained with three types of operation: Capsulotomy, capsulotomy with capsulectomy, and intracap sular extraction. These figures indicate that the main dif ferences in incidence of complications fol lowing intracapsular and extracapsular cata ract extraction, in our hands at least, are: 1. Higher incidence of striate keratitis following intracapsular extraction (although in practically every case this had cleared entirely by the ninth postoperative d a y ) . 2. Higher incidence of delayed formation of the anterior chamber following intracap sular extraction (of the 57 cases of delayed anterior chamber formation following intra capsular extraction the anterior chamber re formed spontaneously in 50 cases). 3. Higher incidence of cortex in the ante rior chamber following capsulotomy. 4. Higher incidence of visible capsule
OPHTHALMOLOGIC
in the anterior chamber or pupil following capsulotomy. These latter two complications apparently are the cause of the somewhat lower per centage of good visual results following capsulotomy as compared to the results fol lowing intracapsular extraction—87.3 per cent versus 93.4 percent. SUMMARY
A study of 1,000 cataract extractions per formed over a seven-month period in a mis sion hospital in Pakistan is presented. A comparison is made between the inci dence of complication after intracapsular and extracapsular lens extraction and a compari son is made between the rough visual results following the two methods. American Mission Hospital. • Since this paper was submitted for publication, the cause of this unusually high incidence of striate keratitis has been discovered and will be the subject of a subsequent report.
HYDROSTATIC
PRESSURE
SYNDROME*
DONALD J. LYLE, M . D . Cincinnati, Ohio J O H N P . S T A P P , COL. ( M C ) U . S . A . F . HoUoman Air Force Base, New Mexico AND RICHARD R. BUTTON, M . D . Newport Beach, California
Escape from military aircraft in flight by means of an ejection seat exposes the occu pant to prolonged high decelerative forces which may be injurious or lethal at super sonic speeds. In experiments conducted by Stapp,^ a rocket-propelled sled on rails, de celerated by a braking system that repro* Presented at the 92nd annual meeting of the American Ophthalmological Society, Hot Springs, Virginia, June, 1956.
duces the forces encountered in supersonic escape from aircraft, has been used to de termine voluntary tolerance limits of ex posure on human subjects. Criteria for tolerance are incipient rever sible injuries, as well as the subjective evaluation. By this means it has been ex perimentally established that a human sub ject seated facing forward, exposed to de celeration perpendicular to the long axis of
E V I S C E R A T I O N
REFERENCES
1. Berens, C.: Synthetic plastic material for implantation into orbit. Am. J. Ophth., 24:550 (May) 1941. 2. Berens, C, and Rosa, F. A.: Evisceration with plastic intrascleral implants. Am. J. Ophth., 36:356 (Mar.) 1953. 3. Ruedemann, A. D.: Evisceration with retention of the cornea. Tr. Am. Ophth. Soc, 1956. 4. Poulard, Α.: Insertion sclerale de spheres et ovoids solides. Ann. ocul., 173:120, 1936. 5. King, J. H., Jr.: Personal communication, June, 1956. 6. Hughes, W. L.: Integrated implants and artificial eyes for use after enucleation and evisceration. Am. J. Ophth, 31:303 (Mar.) 1948. 7. deSchweinitz, G. E.: The comparative value of implants and the operation which has been substituted for it. Compt rend. Sect, opht., Internat. Med. Cong., Paris, 19(X), pp. 39-56. 8. Gifford, H.: On sympathetic ophthalmia after evisceration and Mules operation. Ophth. Ree, 17:584, 1908. 9. Guyton, J. S.: Enucleation and allied procedures: A review and description of a new operation. Tr. Am. Ophth. Soc, 1948, v. 46. 10. Gat, von L.: Ultraseptyl-Einstreuung in Eviszerationsstumpfe. Ophthalmologica, 117:343 (June) 1949. 11. Summerskill, W. H.: Modifications and defense of the scleral implant. Brit. J. Ophth., 37:415, 1953. 12. Berens, C.: An illimiinated retractor for eye operations. Am. J. Ophth., 27:281 (Mar.) 1944. 13. : A plastic compressor for enucleation and evisceration. J.A.M.A., 149:1316 (Aug.) 1952. A
STUDY
O F 1,000 C A T A R A C T
EXTRACTIONS
N . E . CHRISTY, M . D . Taxila,
I n some countries, Pakistan, India, and several countries in Africa, for example, there are remarkable opportunities and need for ophthalmic surgery. I n some cases this surgery must be performed under conditions w^hich by American standards might be con sidered somewhat primitive but still, in many instances, quite satisfactory results are ob tained. The present report of a series of cataract extractions performed in a mission hospital in Pakistan is presented ( 1 ) t o acquaint American readers with the opportunities for ophthalmic surgery in some other countries ( 2 ) to present a comparison of the incidence of complications during and following cata ract extraction by the intracapsular method and by the capsulotomy o r so-called extra capsular method, and ( 3 ) to report the inci dence of complications following cataract ex traction without the use of sutures. Since present-day training of residents in ophthalmology in the United States stresses the use of intracapsular methods with the use of corneoscleral o r some other type of suture, it was felt that the data presented
Pakistan
in this report might be of interest for pur poses of comparison. T h e 1,000 cataract extractions reported in this article were performed during a sevenmonth period, September, 1955, t o March, 1956, in the American Mission Hospital, Taxila, Pakistan. T h e patients were mostly Pakistani village farmers some of whom had very little conception of cleanliness o r sterility and little idea of what was expected of them in a hospital. Most of the opera tions (935 cases) were performed by one surgeon. In this hospital patients are seen for the first time in an afternoon out-patient clinic and those having cataracts o r other condi tions requiring surgery a r e admitted. A urinalysis is performed; the patient's lids and face are cleaned; and a sterile pad is applied t o the eye t o be operated upon. Phenobarbital (1.5 gr.) is given the night before operation. O n the morning of operation each patient is given phenobarbital (3.0 g r . ) and chlorpromazine (25 m g . ) . T h e patients walk t o the operating room where the pad is re-
650
Ν. Ε. TABLE TYPES
OF
Type of cataract Immature Mature senile Intumescent Hypermature Morgagnian Juvenile Traumatic Complicated
I
CATARACT
Number 54 755 40 102 9 12 11 40
moved and examined. Those having exces sive or purulent discharge have their opera tions postponed and are started on an anti biotic. Pontocaine is used for topical anesthesia and the tension is measured. A Van Lint block is administered by a nurse and a retro bulbar injection of 2.0-percent procaine with hyaluronidase is administered by the sur geon. The lids are scrubbed with a 1:5,000 Zephiran solution, a speculum is inserted, and the conjunctival sac flushed with 1:5,000 Zephiran. The incision is made with a von Graefe knife through the apparent corneo-scleral junction in the upper one half of the cornea. A s the knife emerges superiorly it is ro tated slightly so as to be more tangent to the globe. The incision is carried on u p under the conjunctiva leaving an intact bridge con junctiva 2.0 to 3.0 mm. wide and 6.0 to 8.0 mm. long. A basal iridectomy is performed in the 12-o'clock meridian. The lens is then removed either extracapsularly after a capsulotomy has been performed or intracapsularly. F o r the extracapsular extraction, the superior lip of the wound is depressed with a lens loop and the lens expressed by pres sure applied below with a muscle hook. F o r the intracapsular extraction, the conjunctival bridge is elevated with a muscle hook and the capsule forceps or erisophake is applied to the lens under direct vision and the lens slid out under the bridge. T h e iris pillars are replaced as necessary and sterile sulfamezathine (or sulfanilamide) powder and peni cillin ointment (25,000 units per cc.) are placed in the eye and both eyes bandaged.
CHRISTY
Sutures are used only in selected cases— unusually unco-operative patients, mentally disturbed patients, those having chronic coughs which could not be adequately con trolled, asthmatics, or those who feel for some reason that they cannot lie flat in bed. In this series of 1,000 operations sutures were used in only 37 cases. T h e patients are carried back to their beds and are kept in bed for eight days. T h e eye is dressed every other day and the unoper ated left uncovered after the first dressing. In some cases both eyes are operated upon on the same day. On a busy morning 40, 50, or 60 cataract operations may be performed. Patients are generally discharged on the ninth postoperative day. Those wishing glasses are advised to return to the hospital in one month for refraction. Although exact statistics concerning the incidence of cataracts in Pakistan are not available, a suggestion of the incidence may be obtained from the fact that during the period in which these 1,000 cataract opera tions were performed 6,000 patients were seen in our eye out-patient department, roughly one cataract for every six patients coming to the hospital with eye complaints. It should be noted however that most of our patients are illiterate so a relatively small percentage of the patients come because of refractive errors. The distribution of cataract types is shown by the data in Table 1. TABLE
2
T Y P E OF OPERATION
PERFORMED
Capsulotomy 365 with capsulectomy 96 Intracapsular extraction 610 Lens forceps applied above middle of lens and lens slid out under intact conjunctival bridge 524 Lens forceps applied below middle of lens and lens tumbled 41 Erisophake extraction 34 Lens forceps applied above middle of lens and zonule stripped 3 Smith extraction, pressure only 8 Burst capsules in all types of intra capsular extractions 50 Vectis delivery- with lens loop Linear extraction
33 12
ONE THOUSAND CATARACT EXTRACTIONS
651
TABLE 3 INCIDENCE OF COMPUCATIONS AND VISUAL RESULTS
All Operations 1,000 Cases
Capsulo tomy 365 Cases
Capsulotomy with Capsulectomy 96 Cases
Intracapsular Extraction 610 Cases
Complication
No.
Percent
No.
Percent
No.
Percent
No.
Percent
Vitreous loss one plus two plus three plus •Total
22 11 4
2.2 1.1 0.4 3.7
11 5 2
3.0 1.3 0.5 4.8
•1 2 0
1.0 2.0
8 5 0
1.3 0.8
317 79 9
31.7 7.9 0.9 40.5
95 22 5
26.0 6.0 1.3 33.3
34 3 1
35.0 3.0 1.0 39.0
218 55 4
35.8 9.0 0.6 45.4
tDelayed formation of anterior chamber
70
7.0
13
3.6
7
7.0
57
9.3
jNonformation of an terior chamber
8
0.8
2
0.5
2
2.0
5
0.8
SO 16 4
5.0 1.6 0.4 7.0
47 14 3
12.8 4.0 0.8 17.6
7 2 2
7.0 2.0 2.0 11.0
2 3 0
0.3 O.S
2.0 2.0
5 6 0 0 5 3 0
0.8 1.0
Striate keratitis/ one plus two plus three plus Total
Cortex in AC one plus two plus three plus Total
3.0
—-
2.1
0.8
Capsule visible in an terior chamber Iris prolapse Infection Choroidal hemorrhage Conjunctival edema Needling required Bulging wound Secondary suture of wound required SU-shaped pupil Boat-shaped pupil
82 13 2 1 8 18 8
8.2 1.3 0.2 0.1 0.8 1.8 0.8
77 7 2 1 3 14 4
21.0 1.9 0.5 0.3 0.8 3.8 1.1
2 2 0 0 0 0 0
6 150 5
0.6 15.0 0.5
2 51 2
0.6 13.9 O.S
0 14 0
14.5
3 98 3
O.S 16.1 0.5
irVision (of 912 cases) VG vision CF vision Η Μ vision LP only
841 46 19 6
91.9 5.0 2.1 0.7
295 29 13 1
87.3 8.1 3.6 0.3
82 7 6 1
91.1 7.0 6.0 1.0
537 16 6 6
93.4 2.6 1.0 1.0
.
.
0.8 0.5
* Of the 33 cases in which the lens was delivered with the lens loop, vitreous was lost in 11 cases. t Delayed formation of anterior chamber indicates the anterior chamber was not formed at the first dressing but reformed (with only atropine drops) during the first nine postoperative days. t Nonformation of anterior chamber indicates that the anterior chaml)er was not formed at the end of nine postoperative days. S Anythmg other than a keyhole-shaped pupil was considered a complication. 1! Unfortunately a visual result is not recorded for every case, in some cases through neglect and in other cases because the patient having discovered that he was able to see satisfactorily left the hospital of his own accord without waiting for further examinations or for discharge. Actual testing of postoperative visual results is in many cases difiicult since 80 to 90 percent of the patients are illiterate. Consequently a rough classification of postoperative vision has been established with four classes of visual results:—• VG stands for "vision good" and indicates that the patient counts fingers at three to four feet with no doubt nor hesitation on the ninth postoperative day; CF stands for "countsfingers"and indicates that the patient counts fingers at three to four feet but with some effort or hesitation; Η Μ indicates that the patient sees only hand movements; and LP indicates light perception only.
Ν. Ε. CHRISTY
652
The types of operation performed are shown in Table 2. Table 3 compares the incidence of compli cations and the visual results obtained with three types of operation: Capsulotomy, capsulotomy with capsulectomy, and intracap sular extraction. These figures indicate that the main dif ferences in incidence of complications fol lowing intracapsular and extracapsular cata ract extraction, in our hands at least, are: 1. Higher incidence of striate keratitis following intracapsular extraction (although in practically every case this had cleared entirely by the ninth postoperative d a y ) . 2. Higher incidence of delayed formation of the anterior chamber following intracap sular extraction (of the 57 cases of delayed anterior chamber formation following intra capsular extraction the anterior chamber re formed spontaneously in 50 cases). 3. Higher incidence of cortex in the ante rior chamber following capsulotomy. 4. Higher incidence of visible capsule
OPHTHALMOLOGIC
in the anterior chamber or pupil following capsulotomy. These latter two complications apparently are the cause of the somewhat lower per centage of good visual results following capsulotomy as compared to the results fol lowing intracapsular extraction—87.3 per cent versus 93.4 percent. SUMMARY
A study of 1,000 cataract extractions per formed over a seven-month period in a mis sion hospital in Pakistan is presented. A comparison is made between the inci dence of complication after intracapsular and extracapsular lens extraction and a compari son is made between the rough visual results following the two methods. American Mission Hospital. • Since this paper was submitted for publication, the cause of this unusually high incidence of striate keratitis has been discovered and will be the subject of a subsequent report.
HYDROSTATIC
PRESSURE
SYNDROME*
DONALD J. LYLE, M . D . Cincinnati, Ohio J O H N P . S T A P P , COL. ( M C ) U . S . A . F . HoUoman Air Force Base, New Mexico AND RICHARD R. BUTTON, M . D . Newport Beach, California
Escape from military aircraft in flight by means of an ejection seat exposes the occu pant to prolonged high decelerative forces which may be injurious or lethal at super sonic speeds. In experiments conducted by Stapp,^ a rocket-propelled sled on rails, de celerated by a braking system that repro* Presented at the 92nd annual meeting of the American Ophthalmological Society, Hot Springs, Virginia, June, 1956.
duces the forces encountered in supersonic escape from aircraft, has been used to de termine voluntary tolerance limits of ex posure on human subjects. Criteria for tolerance are incipient rever sible injuries, as well as the subjective evaluation. By this means it has been ex perimentally established that a human sub ject seated facing forward, exposed to de celeration perpendicular to the long axis of