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Intraocular Pressure Measurement in Infants Under General Anesthesia
INTRAOCULAR PRESSURE MEASUREMENT IN INFANTS UNDER GENERAL A N E S T H E S I A ALFREDO DOMINGUEZ, M.D., M. SANCHEZ BANOS, M.D., M. GIMENEZ ALVAREZ, M.D., G. FERNANDEZ CONTRA, M.D., AND F. BENITO QUINTELA, M.D.
Madrid, Spain
Opinions concerning normal intraocular pressure in anesthetized infants differ con siderably because several studies1"8 have yielded different results (Table 1). The an esthetic agents used and/or the deepness of anesthesia partly explain the discrepancies. In addition, the scleral rigidity in infants is tonometrically higher than in adults,3 making indentation tonometry less reliable. This fac tor has less influence in applanation tonom etry.5"9 We used applanation tonometry to mea sure the intraocular pressure in normal in fants in an attempt to establish the basal in traocular pressure in infants and to achieve a standardized procedure for administering general anesthesia for applanation tonometry in infants. We divided the study into three parts: Group 1 included children up to the age of 5 years operated for strabismus under gen eral anesthesia. Groups 2-7 included infants under 1 year of age admitted for general surgery. We measured without mydriatics the intraocular pressure in 283 eyes sup posedly free of disease. The limitations in this part (Groups 2-7) were that (1) the ophthalmic procedure did not dictate the de gree and type of general anesthesia, and (2) the hours of waiting at the various hospitals were long. Group 8 included infants under 1 year of age who had lacrimal problems. The study was in our own hospital and our standardized ophthalmic anesthesia proce dure was used. MATERIALS AND METHODS
Group 1—The intraocular pressure of children from 10 months to 5 years of age, From the National Ophthalmological Institute, Department of Health, Madrid, Spain. Reprint requests to Alfredo Dominguez, M.D., Velazquez, 75, Madrid 6, Spain.
anesthetized for strabismus surgery, was measured as soon as the child was quiet and the eyes were in good position for tonom etry. In some cases, this was before intu bation. For anesthesia, most of the children re ceived atropine premedication. Halothane, N 2 0, and Q 2 provided induction and main tenance; intubation was with succinylcholine. Groups 2-7—The second part of our study took place in four Madrid hospitals with active pediatric surgical services. Infants up to 12 months of age with no known ocular disease were examined under anesthesia for general surgery. Three different applanation tonometers were used to measure the intra ocular pressure: the Draeger, the GarciaSanchez, and the Perkins manual instru ments. Most often, the intraocular pressure was measured when the anesthesia was deep. However, in some cases, busy surgical ses sions or short anesthesia made this impos sible, especially when only halothane (Group 4) was used for short interventions or ex plorations, and the anesthetic level only seemed deep. The broad variations in intra ocular pressure reflect this circumstance. In procedures of long duration that permitted more than one tonometric measurement, we accepted the lowest reading. The data ob tained were classified according to the type of anesthesia used. GROUP 2—Atropine premedication; halo thane, N 2 0 , and 0 2 induction and mainte nance ; succinylcholine intubation. GROUP 3—Promethazine, chlorpromazine,
atropine premedication; halothane, N 2 0 , and 0 2 induction and maintenance; succinylcho line intubation. GROUP A—Atropine premedication; halo110
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111
INTRAOCULAR P R E S S U R E IN I N F A N T S TABLE 1
NORMAL INTRAOCULAR PRESSURE IN INFANTS UNDER GENERAL ANESTHESIA
Study Barkan 1 (1953) Apt 1 (1957) Ytteborg* (1960) Kornblueth and associates* (1962) Manzitti and Darnel 6 (1964) Sampaolesi, Reca, and Carro* (1967) Hetherington and Shaffer7 (1968) Carvalho and Calixto 8 (1970)
No. of Eyes 20 46 103
47 36 48 30 34
Age 2 mo to 2yr 3 mo to 4 yr 5 mo to 10 yr 5 to 24 hours 1 mo to 2yr 1 mo to 5yr 3 mo to 7yr 15 days to 4 yr
Tonometer
Mean, mm Hg
Limits, mm Hg
Schi^tz
Not given
20/28
Schifftz
Not given
11/24
Comment
Not given Infants under 5 months old eliminated; high pressure attributed to poor anesthesia 15.9/29
Schi^tz
17.7
Schijftz
21.55
Goldmann
16.94
12/20
SD = 1.90
Goldmann
10.56
4/16
SD = 1.01
Draeger and Schijftz Goldmann
12.5
7/22
10.32
7.5/14.5
thane, N 2 0 , and 0 2 induction and mainte nance; no intubation. GROUP 5—Atropine premedication; halothane, N 2 0 , and 0 2 induction and mainte nance; either intubated without succinylcholine or tonometry performed more than one hour after succinylcholine intubation. GROUP 6—Atropine premedication; thiopental (Pentothal), ether, N 2 0 , and 0 2 in duction and maintenance; succinylcholine in tubation. GROUP 7—Pentobarbital (Nembutal) sup positories, 10 to 20 mg/kg. To counteract inaccuracies due to the vari ous ophthalmologists and tonometers em ployed, we performed a blind control in 12 infants (24 eyes) who fulfilled the general requirements. Three of us, each with one applanation tonometer, and a fourth examiner, with an electronic tonometer for comparison, measured the intraocular pressure and re corded the findings. To circumvent the influ ence of always being the first or always the last examiner, the order in which we per formed tonometry was routinely shifted. The arithmetic mean (Table 2) of the data of each observer and each tonometer
SD = 1.88
indicated that 0.5 mm Hg was an acceptable error. Group 8—In the third part of our study, we measured the intraocular pressure with a Draeger applanation tonometer in infants under 1 year of age with lacrimal prob lems in whom it was difficult to probe the canaliculus and lacrimal sac. There was no premedication. The anesthetic mixture, ad ministered with a mask, included halothane 0.5%, N 2 0 80%, and 0 2 20%, during the first minute; halothane 1%, N 2 0 75%, and 0 2 25% during the second and third min utes; and halothane 1.5%, N 2 0 66%, and 0 2 33% during the fourth minute. At the end of the second minute, one drop of a TABLE 2 M E A N S OF VARIOUS TONOMETERS ON THE SAME 1 2 INFANTS
Tonometer Draeger manual applanation tonometer Garcia-Sanchez manual applanation tonometer Perkins manual applanation tonometer Mackay-Marg electronic tonometer
Mean,
mm Hg 13.04 12.67 12.41 14.04
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TABLE 3 INTRAOCULAR PRESSURE I N NORMAL INFANTS UNDER VARIOUS ANESTHETIC PROCEDURES
Group*
Premedication and Anesthesia
No. of Eyes
Most with atropine, halothane, N 2 0 , 95 0 2 (intubation with succinylcholine) Atropine, halothane, N 2 0 , 0 2 (intu- 175 bation with succinylcholine) Promethazine, chlorpromazine, atro- 40 pine, halothane, N2O, 0 2 (intuba tion with succinylcholine) Atropine, halothane, N 2 0 , 0 2 (with20 out intubation) Atropine, halothane, N 2 0 , 0 2 (intu28 bated without succinylcholine or one hour after intubation) 12 Atropine, thiopental, ether, N2Q, 0 2 (intubation with succinylcholine) Pentobarbital suppositories, 10 to 20 8 mg/kg Standardized 30
Mean, mm Hg
SD
Limits, mm Hg
Draeger
14.7
4.6
27/7
Draeger, Garcia-Sanchez, or Perkins Draeger, Garcia-Sanchez, or Perkins
14
2.3
8.5/20
13.9
3.7
7/24
Draeger, Garcia-Sanchez, or Perkins Draeger, Garcia-Sanchez, or Perkins
13.8
5.7
5/23
13.5
2.7
7/17.5
Draeger, Garcia-Sanchez, or Perkins Draeger, Garcia-Sanchez, or Perkins Draeger
11.6
3.9
5/16.5
11
3.8
5/14
2.66
5/14
Tonometer
9.56
* Group 1, 10 months to 5 years old; Groups 2-8, up to 12 months old.
topical anesthesia was applied to each eye; if the infant moved, during the fourth min ute, administration of halothane 1.5% was in creased to\y2 minutes. Anesthetic inhalation was then stopped, and the infant inspired only air. The infant usually slept for two or more minutes, sufficient time for taking several intraocular pressure measurements. This is our standardized anesthesia proce dure and the one we recommend for exam ining infants with congenital glaucoma. Our experience showed that, usually, the intra ocular pressure was lowest just before the child began to revive. However, one must start measurements promptly, for the dura tion of anesthesia is uncertain. RESULTS
Table 3 summarizes our results. The in traocular pressure curves acquired during anesthesia suggested the following: 1. The more relaxed the infant, the lower the intraocular pressure. This was not re lated to the blood concentration of the anes thetic. 2. Intubation (if the child's breathing was not good) lowered the intraocular pressure.
If the airway was clear, intubation increased the intraocular pressure (Fig. 1) because the diameter of the tube was smaller than the natural airway and introduction of the tube produced irritation. 3. Inhalation of the anesthetic agent acted as an irritant. When the infant breathed only air, he became more relaxed and the intraocular pressure further decreased. In most cases (Fig. 2), the intraocular pressure fell progressively as anesthesia con tinued, to reach a low level between the third and fourth minutes. When respira tion was freed, the intraocular pressure dropped to a lower level. This suggests that relaxation and easy breathing are more im portant than the anesthetic blood level. In some cases, the infant relaxed quickly (Fig. 3), and the intraocular pressure fell to its lowest level in one minute. Further anesthesia and free breathing did not lower the readings, which suggests that basal intra ocular pressure was reached at the outset. DISCUSSION
Our results support other studies6"8 in which applanation tonometry obtained intra-
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INTRAOCULAR PRESSURE IN INFANTS
as close to the model as practical possibilities permit. Basal intraocular pressures differ when the subject is seated or recumbent. We con sidered only the recumbent position, since placing an anesthetized infant in a vertical position is not without danger, and a precise tonometric reading is impossible in an alert child. It would be ideal if one could mea sure the basal intraocular pressure when the infant is in a relaxed physiologic sleep al-
is 16 -
113
INTUBATION WITHOUT S-COLINE
I » u CO CO 111
K 8 0. ATROPINE- HALOTHANE- N 2 0 - 0 2
—
6 -
«0
X ■ ■ '
5
i
10
15
i
i
i
i
i
i
20
E E
30
UJ
20
3 CO CO UJ
10 -
ANESTHETIC MIXTURE STOPPED
MINUTES
Fig. 1 (Dominguez, Banos, Alvarez, Contra, and Quintela). Because anesthesia took a longer time than estimated, the anesthesiologist decided to use intubation. Good relaxation made succinylcholine (s-coline) unnecessary.
ocular pressure levels in normal infants that were definitely lower than the average intra ocular pressure levels in adults. Variations in tonometric readings differ markedly in infants and adults. If a nonstandardized an esthesia regimen is used, variations in in fants can be extremely high5"9 (Groups 1 and 4). In unanesthetized newborn infants, a com plementary study with the Mackay-Marg electronic tonometer showed wide variations in the physiologic intraocular pressure of the same eye over short periods of time. It is no wonder that published reports differ (Table 1). We observed that a relaxed baby free of respiratory disturbances has a low intraocu lar pressure. The basal intraocular pressure, the lowest that the eye can reach under the most favorable conditions, is a theoretic model difficult to attain. However, the con cept is useful in that it forces one to come
oc
STANDARDIZED ANESTHESIA
oc a.
MINUTES
Fig. 2 (Dominguez, Banos, Alvarez, Contra, and Quintela). The infant was still crying at the end of the first minute. Within four minutes, the intraocu lar pressure fell sharply.
I 12 £ E
V
10
£
3 CO
CO 111
tc 0.
n 8
BABY AWAKES
ANESTHETIC MIXTURE STOPPED
STANDARDIZED ANESTHESIA
'
'
L
J
I
I
8
L
9
MINUTES
Fig. 3 (Dominguez, Banos, Alvarez, Contra, and Quintela). At the end of the first minute, the infant was completely relaxed.
114
AMERICAN JOURNAL OF OPHTHALMOLOGY
though this is usually impossible. Adult data10 suggest that the basal intraocular pres sure in infants under general anesthesia should be lower than in physiologic sleep. Mackay-Marg electronic tonometry in unanesthetized, relaxed infants frequently ob tained readings between 5 to 10 mm Hg. The intraocular pressure rose immediately at the touch of the probe. We found an arithmetic mean of 13 mm Hg in 604 eyes of newborn babies. We could not consider the mean obtained with the electronic tonom eter a basal intraocular pressure because most of the tracings were obtained when the infant was already disturbed. However, com paring these figures with the ones in Table 3, we can see that the basal intraocular pres sure in a physiologically sleeping, relaxed in fant is not much different from the basal intraocular pressure in an anesthetized re laxed infant. Relaxation is the most important factor influencing low intraocular pressure mea surements in infants. In our opinion, a stan dardized anesthesia procedure permits mea suring the intraocular pressure as close to the basal level as possible. The induction period of the proposed standardized anes thesia lasts longer than some infants need (Fig. 3 ) , but it is sufficient for most other infants (Fig. 2). Even though applanation tonometry helps eliminate rigidity differences, relaxation and easy breathing remain important, even when produced by an anesthetic agent, if one is to obtain the lowest—the basal—intraocular pressure. CONCLUSIONS
Halothane anesthesia may give wide vari ations in intraocular pressure measurements, depending on irritation by the tube, how the position of the head and neck affect venous return, deepness of anesthesia, premedication, and the other anesthetic drugs used. Infants intubated without succinylcholine (Group 5) gave the lowest mean (13.5 mm Hg) with a reasonable higher limit (17.5
JULY, 1974
mm H g ) . The other groups gave higher limits of over 20 mm Hg. Children from 10 months to 5 years of age (Group 1) gave the highest intraocular pressure mean in our study, suggesting that the rise in intraocular pressure in the first years of life might be related to the rise in arterial blood pressure. In the newborn, the lower basal intraocu lar pressure permits good blood flow into the eye. With increased age, the arterial pres sure rises, and a soft eye is not so neces sary. Anesthesia standardized by age groups would allow more valid comparisons. Ether anesthesia with intubation (Group 6) gave the lowest intraocular pressure mea surements. Although the number of cases was small, the cooperation of anesthesiolo gists and surgeons permitted control of the intraocular pressure during the surgical pro cedure. We used the lowest point of the curves obtained. Other workers suggest that halothane decreases the intraocular pressure more than ether, probably because of its rapid induction. However, we found that ether anesthesia can give as low values as halothane. Pentobarbital (Group 7) also gave low intraocular pressure readings, most likely because it produced good relaxation and respiration. Carvalho and Calixto8 also found this to be true. In our experience, how ever, pentobarbital was not always effective, for many infants awakened during the mea surements. Liquid rectal administration is probably more effective than the supposi tories we used. The standardized regimen of anesthesia administration achieved better measure ments. Because it is easy, effective, quick, and safe, it should be used for congenital glaucoma evaluation. Experience and new drugs might, in the future, perfect a more effective procedure. For now, we recom mend our method of anesthesia and applana tion tonometry for intraocular pressure mea surements in infants. The exactness of the procedure eliminates the uncertainties pres ently attending anesthesia in infants.
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INTRAOCULAR PRESSURE IN INFANTS
Our study showed that the intraocular pressure by applanation tonometry is lower in infants than in adults. However, it also showed that variations are wide and fre quent. Standardized anesthesia will reduce these variations to a minimum. Without it, one must accept these wide variations as nor mal. Group 4 clearly demonstrates this. Ap planation tonometry recorded pressure as low as 5 mm Hg and as high as 23 mm Hg in normal eyes. We performed tonometry in Group 4 as the practicing ophthalmologist would be likely to perform it. Experts using indentation tonometry found normal pressures over 20 mm Hg 1 ' 2 ' 4 ' 11 in infants. Some even eliminated from their study infants under the age of 5 months be cause the measurements were constantly under three divisions of the Schiotz tonom eter.3 Applanation tonometry also gave read ing of 20 mm Hg and over.6'7'9 Groups 1-6 in our study showed some examples of this. If anesthetic procedures are not stan dardized, one must presently accept wide variations in intraocular pressure measure ments in normal infants, as they have been accepted in the past (Table 1). With the standardized anesthesia proce dure, Group 8 showed an arithmetic mean of 9.56 mm Hg with a standard deviation of 2.66, giving confidence limits of ± 7.31 mm Hg for 99% of the population. This would make 16.87 mm Hg the border line between normal intraocular pressure and congenital glaucoma. If we applied Student's f-test to distribution, taking into account the number of infants and not the number of eyes, the confidence limits would be slight ly over 17 mm Hg for 99% of the popula tion. Sampaolesi, Reca, and Carro 8 found a low variation (SD 1.01) in 48 eyes of in fants, most of whom were over 1 year old. Other authors 5 ' 8 found a standard deviation in between that of Sampaolesi, Reca, and Carro and our own figures. Clinical experience is necessary before one can fully accept a valid intraocular pres sure border line for congenital glaucoma.
115
With a standardized anesthesia procedure and applanation tonometry, we suggest that an intraocular pressure over 17 mm Hg is border line and that measurements of 20 mm Hg and over are glaucomatous. To avoid further damage to the eye, surgery should be performed when symptoms, such as pho tophobia and lacrimation, accompany pres sures of 20 mm Hg and higher. When the intraocular pressure is between 17 and 20 mm Hg, the infant should under go periodic measurement of the intraocular pressure under standardized anesthesia; if such figures persist, the corneal diameters, the eye volume (echogram), and the study of the optic disk will support the clinical decision. Standardized procedures are used in many clinical tests—adaptation curves, electroretinography, visual fields," and so forth. To yield meaningful results, intraocular pressure measurement in infants demands standard ization. A rise in venous pressure or in extraocular muscle tonus can vary the intra ocular pressure sharply. As a consequence, the intraocular pressure changes constantly in infants. Basal intraocular pressure sup plies the only steady-state for valid compari son. SUMMARY
We measured the intraocular pressure with manual applanation tonometers in 408 eyes of normal infants under general anes thesia. Various anesthesia procedures gave different results. Even with the same type of anesthesia, the higher and lower limits of intraocular pressure varied greatly. Since the level of the intraocular pressure appears to depend primarily on the level of relaxa tion in the infant we recommend applanation tonometry with a standardized anesthesia procedure to obtain the basal intraocular pressure. Using our method to measure the intraocular pressure in 30 normal eyes, we obtained a mean of 9.56 mm Hg with a standard deviation of 2.66. This result sug gested that an applanation measurement of
116
AMERICAN JOURNAL OF OPHTHALMOLOGY
17 mm Hg be considered the upper limit of normal pressure and that one of 20 mm Hg be considered the lower limit of pathologic pressure. Readings in between these two limits should be considered suspicious. ACKNOWLEDGMENTS
We thank the personnel of the Pediatric Services of the Cruz Roja, Nino Jesus, La Paz, and Fran cisco Franco Hospitals for cooperation and as sistance. REFERENCES
1. Barkan, O.: Surgery of congenital glaucoma. Am. J. Ophthalmol. 36:1523, 1953. 2. Apt, L.: Tonography in infantile glaucoma. Am. J. Ophthalmol. 43:624, 1957. 3. Ytteborg, J.: Investigations of the rigidity coefficient in children's eyes. Acta Ophthalmol. 38:658,1960. 4. Kornblueth, W., Abrahamov, A., Aladjemoff,
JULY, 1974
L., Magora, F., and Gombos, G.: Intraocular pres sure in the newborn measured under general anes thesia. Arch. Ophthalmol. 67:750, 1962. 5. Manzitti, E., and Darnel, A.: Valores de la tonometria aplanatica en el lactante normal. Arch. Oftalmol. B. Aires 39:360, 1964. 6. Sampaolesi, R., Reca, R. M., and Carro, A.: Presion ocular en el nino hasta los 5 anos. Arch. Oftalmol. B. Aires 42:180, 1967. 7. Hetherington, J., and Shaffer, R. N.: Tonometry and tonography in congenital glaucoma. In vest. Ophthalmol. 7:134, 1968. 8. Carvalho, C. A., and Calixto, N.: Semilogia do glaucoma congenito. Rev. Bras. Oftalmol. 29:7, 1970. 9. Chandler, P. A., and Grant, W. M.: Lectures in Glaucoma. Philadelphia, Lea and Febiger, 1965, p. 301. 10. Kornblueth, W., Aladjemoff, L., Magora, F., and Gabbay, A.: Influence of general anesthesia on intraocular pressure in man. Arch. Ophthalmol. 61:84, 1959. 11. Scheie, H.: Management of infantile glau coma. Arch. Ophthalmol. 62:35, 1959.
Madrid, Spain
Opinions concerning normal intraocular pressure in anesthetized infants differ con siderably because several studies1"8 have yielded different results (Table 1). The an esthetic agents used and/or the deepness of anesthesia partly explain the discrepancies. In addition, the scleral rigidity in infants is tonometrically higher than in adults,3 making indentation tonometry less reliable. This fac tor has less influence in applanation tonom etry.5"9 We used applanation tonometry to mea sure the intraocular pressure in normal in fants in an attempt to establish the basal in traocular pressure in infants and to achieve a standardized procedure for administering general anesthesia for applanation tonometry in infants. We divided the study into three parts: Group 1 included children up to the age of 5 years operated for strabismus under gen eral anesthesia. Groups 2-7 included infants under 1 year of age admitted for general surgery. We measured without mydriatics the intraocular pressure in 283 eyes sup posedly free of disease. The limitations in this part (Groups 2-7) were that (1) the ophthalmic procedure did not dictate the de gree and type of general anesthesia, and (2) the hours of waiting at the various hospitals were long. Group 8 included infants under 1 year of age who had lacrimal problems. The study was in our own hospital and our standardized ophthalmic anesthesia proce dure was used. MATERIALS AND METHODS
Group 1—The intraocular pressure of children from 10 months to 5 years of age, From the National Ophthalmological Institute, Department of Health, Madrid, Spain. Reprint requests to Alfredo Dominguez, M.D., Velazquez, 75, Madrid 6, Spain.
anesthetized for strabismus surgery, was measured as soon as the child was quiet and the eyes were in good position for tonom etry. In some cases, this was before intu bation. For anesthesia, most of the children re ceived atropine premedication. Halothane, N 2 0, and Q 2 provided induction and main tenance; intubation was with succinylcholine. Groups 2-7—The second part of our study took place in four Madrid hospitals with active pediatric surgical services. Infants up to 12 months of age with no known ocular disease were examined under anesthesia for general surgery. Three different applanation tonometers were used to measure the intra ocular pressure: the Draeger, the GarciaSanchez, and the Perkins manual instru ments. Most often, the intraocular pressure was measured when the anesthesia was deep. However, in some cases, busy surgical ses sions or short anesthesia made this impos sible, especially when only halothane (Group 4) was used for short interventions or ex plorations, and the anesthetic level only seemed deep. The broad variations in intra ocular pressure reflect this circumstance. In procedures of long duration that permitted more than one tonometric measurement, we accepted the lowest reading. The data ob tained were classified according to the type of anesthesia used. GROUP 2—Atropine premedication; halo thane, N 2 0 , and 0 2 induction and mainte nance ; succinylcholine intubation. GROUP 3—Promethazine, chlorpromazine,
atropine premedication; halothane, N 2 0 , and 0 2 induction and maintenance; succinylcho line intubation. GROUP A—Atropine premedication; halo110
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111
INTRAOCULAR P R E S S U R E IN I N F A N T S TABLE 1
NORMAL INTRAOCULAR PRESSURE IN INFANTS UNDER GENERAL ANESTHESIA
Study Barkan 1 (1953) Apt 1 (1957) Ytteborg* (1960) Kornblueth and associates* (1962) Manzitti and Darnel 6 (1964) Sampaolesi, Reca, and Carro* (1967) Hetherington and Shaffer7 (1968) Carvalho and Calixto 8 (1970)
No. of Eyes 20 46 103
47 36 48 30 34
Age 2 mo to 2yr 3 mo to 4 yr 5 mo to 10 yr 5 to 24 hours 1 mo to 2yr 1 mo to 5yr 3 mo to 7yr 15 days to 4 yr
Tonometer
Mean, mm Hg
Limits, mm Hg
Schi^tz
Not given
20/28
Schifftz
Not given
11/24
Comment
Not given Infants under 5 months old eliminated; high pressure attributed to poor anesthesia 15.9/29
Schi^tz
17.7
Schijftz
21.55
Goldmann
16.94
12/20
SD = 1.90
Goldmann
10.56
4/16
SD = 1.01
Draeger and Schijftz Goldmann
12.5
7/22
10.32
7.5/14.5
thane, N 2 0 , and 0 2 induction and mainte nance; no intubation. GROUP 5—Atropine premedication; halothane, N 2 0 , and 0 2 induction and mainte nance; either intubated without succinylcholine or tonometry performed more than one hour after succinylcholine intubation. GROUP 6—Atropine premedication; thiopental (Pentothal), ether, N 2 0 , and 0 2 in duction and maintenance; succinylcholine in tubation. GROUP 7—Pentobarbital (Nembutal) sup positories, 10 to 20 mg/kg. To counteract inaccuracies due to the vari ous ophthalmologists and tonometers em ployed, we performed a blind control in 12 infants (24 eyes) who fulfilled the general requirements. Three of us, each with one applanation tonometer, and a fourth examiner, with an electronic tonometer for comparison, measured the intraocular pressure and re corded the findings. To circumvent the influ ence of always being the first or always the last examiner, the order in which we per formed tonometry was routinely shifted. The arithmetic mean (Table 2) of the data of each observer and each tonometer
SD = 1.88
indicated that 0.5 mm Hg was an acceptable error. Group 8—In the third part of our study, we measured the intraocular pressure with a Draeger applanation tonometer in infants under 1 year of age with lacrimal prob lems in whom it was difficult to probe the canaliculus and lacrimal sac. There was no premedication. The anesthetic mixture, ad ministered with a mask, included halothane 0.5%, N 2 0 80%, and 0 2 20%, during the first minute; halothane 1%, N 2 0 75%, and 0 2 25% during the second and third min utes; and halothane 1.5%, N 2 0 66%, and 0 2 33% during the fourth minute. At the end of the second minute, one drop of a TABLE 2 M E A N S OF VARIOUS TONOMETERS ON THE SAME 1 2 INFANTS
Tonometer Draeger manual applanation tonometer Garcia-Sanchez manual applanation tonometer Perkins manual applanation tonometer Mackay-Marg electronic tonometer
Mean,
mm Hg 13.04 12.67 12.41 14.04
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AMERICAN JOURNAL O F OPHTHALMOLOGY
J U L Y , 1974
TABLE 3 INTRAOCULAR PRESSURE I N NORMAL INFANTS UNDER VARIOUS ANESTHETIC PROCEDURES
Group*
Premedication and Anesthesia
No. of Eyes
Most with atropine, halothane, N 2 0 , 95 0 2 (intubation with succinylcholine) Atropine, halothane, N 2 0 , 0 2 (intu- 175 bation with succinylcholine) Promethazine, chlorpromazine, atro- 40 pine, halothane, N2O, 0 2 (intuba tion with succinylcholine) Atropine, halothane, N 2 0 , 0 2 (with20 out intubation) Atropine, halothane, N 2 0 , 0 2 (intu28 bated without succinylcholine or one hour after intubation) 12 Atropine, thiopental, ether, N2Q, 0 2 (intubation with succinylcholine) Pentobarbital suppositories, 10 to 20 8 mg/kg Standardized 30
Mean, mm Hg
SD
Limits, mm Hg
Draeger
14.7
4.6
27/7
Draeger, Garcia-Sanchez, or Perkins Draeger, Garcia-Sanchez, or Perkins
14
2.3
8.5/20
13.9
3.7
7/24
Draeger, Garcia-Sanchez, or Perkins Draeger, Garcia-Sanchez, or Perkins
13.8
5.7
5/23
13.5
2.7
7/17.5
Draeger, Garcia-Sanchez, or Perkins Draeger, Garcia-Sanchez, or Perkins Draeger
11.6
3.9
5/16.5
11
3.8
5/14
2.66
5/14
Tonometer
9.56
* Group 1, 10 months to 5 years old; Groups 2-8, up to 12 months old.
topical anesthesia was applied to each eye; if the infant moved, during the fourth min ute, administration of halothane 1.5% was in creased to\y2 minutes. Anesthetic inhalation was then stopped, and the infant inspired only air. The infant usually slept for two or more minutes, sufficient time for taking several intraocular pressure measurements. This is our standardized anesthesia proce dure and the one we recommend for exam ining infants with congenital glaucoma. Our experience showed that, usually, the intra ocular pressure was lowest just before the child began to revive. However, one must start measurements promptly, for the dura tion of anesthesia is uncertain. RESULTS
Table 3 summarizes our results. The in traocular pressure curves acquired during anesthesia suggested the following: 1. The more relaxed the infant, the lower the intraocular pressure. This was not re lated to the blood concentration of the anes thetic. 2. Intubation (if the child's breathing was not good) lowered the intraocular pressure.
If the airway was clear, intubation increased the intraocular pressure (Fig. 1) because the diameter of the tube was smaller than the natural airway and introduction of the tube produced irritation. 3. Inhalation of the anesthetic agent acted as an irritant. When the infant breathed only air, he became more relaxed and the intraocular pressure further decreased. In most cases (Fig. 2), the intraocular pressure fell progressively as anesthesia con tinued, to reach a low level between the third and fourth minutes. When respira tion was freed, the intraocular pressure dropped to a lower level. This suggests that relaxation and easy breathing are more im portant than the anesthetic blood level. In some cases, the infant relaxed quickly (Fig. 3), and the intraocular pressure fell to its lowest level in one minute. Further anesthesia and free breathing did not lower the readings, which suggests that basal intra ocular pressure was reached at the outset. DISCUSSION
Our results support other studies6"8 in which applanation tonometry obtained intra-
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as close to the model as practical possibilities permit. Basal intraocular pressures differ when the subject is seated or recumbent. We con sidered only the recumbent position, since placing an anesthetized infant in a vertical position is not without danger, and a precise tonometric reading is impossible in an alert child. It would be ideal if one could mea sure the basal intraocular pressure when the infant is in a relaxed physiologic sleep al-
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ocular pressure levels in normal infants that were definitely lower than the average intra ocular pressure levels in adults. Variations in tonometric readings differ markedly in infants and adults. If a nonstandardized an esthesia regimen is used, variations in in fants can be extremely high5"9 (Groups 1 and 4). In unanesthetized newborn infants, a com plementary study with the Mackay-Marg electronic tonometer showed wide variations in the physiologic intraocular pressure of the same eye over short periods of time. It is no wonder that published reports differ (Table 1). We observed that a relaxed baby free of respiratory disturbances has a low intraocu lar pressure. The basal intraocular pressure, the lowest that the eye can reach under the most favorable conditions, is a theoretic model difficult to attain. However, the con cept is useful in that it forces one to come
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though this is usually impossible. Adult data10 suggest that the basal intraocular pres sure in infants under general anesthesia should be lower than in physiologic sleep. Mackay-Marg electronic tonometry in unanesthetized, relaxed infants frequently ob tained readings between 5 to 10 mm Hg. The intraocular pressure rose immediately at the touch of the probe. We found an arithmetic mean of 13 mm Hg in 604 eyes of newborn babies. We could not consider the mean obtained with the electronic tonom eter a basal intraocular pressure because most of the tracings were obtained when the infant was already disturbed. However, com paring these figures with the ones in Table 3, we can see that the basal intraocular pres sure in a physiologically sleeping, relaxed in fant is not much different from the basal intraocular pressure in an anesthetized re laxed infant. Relaxation is the most important factor influencing low intraocular pressure mea surements in infants. In our opinion, a stan dardized anesthesia procedure permits mea suring the intraocular pressure as close to the basal level as possible. The induction period of the proposed standardized anes thesia lasts longer than some infants need (Fig. 3 ) , but it is sufficient for most other infants (Fig. 2). Even though applanation tonometry helps eliminate rigidity differences, relaxation and easy breathing remain important, even when produced by an anesthetic agent, if one is to obtain the lowest—the basal—intraocular pressure. CONCLUSIONS
Halothane anesthesia may give wide vari ations in intraocular pressure measurements, depending on irritation by the tube, how the position of the head and neck affect venous return, deepness of anesthesia, premedication, and the other anesthetic drugs used. Infants intubated without succinylcholine (Group 5) gave the lowest mean (13.5 mm Hg) with a reasonable higher limit (17.5
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mm H g ) . The other groups gave higher limits of over 20 mm Hg. Children from 10 months to 5 years of age (Group 1) gave the highest intraocular pressure mean in our study, suggesting that the rise in intraocular pressure in the first years of life might be related to the rise in arterial blood pressure. In the newborn, the lower basal intraocu lar pressure permits good blood flow into the eye. With increased age, the arterial pres sure rises, and a soft eye is not so neces sary. Anesthesia standardized by age groups would allow more valid comparisons. Ether anesthesia with intubation (Group 6) gave the lowest intraocular pressure mea surements. Although the number of cases was small, the cooperation of anesthesiolo gists and surgeons permitted control of the intraocular pressure during the surgical pro cedure. We used the lowest point of the curves obtained. Other workers suggest that halothane decreases the intraocular pressure more than ether, probably because of its rapid induction. However, we found that ether anesthesia can give as low values as halothane. Pentobarbital (Group 7) also gave low intraocular pressure readings, most likely because it produced good relaxation and respiration. Carvalho and Calixto8 also found this to be true. In our experience, how ever, pentobarbital was not always effective, for many infants awakened during the mea surements. Liquid rectal administration is probably more effective than the supposi tories we used. The standardized regimen of anesthesia administration achieved better measure ments. Because it is easy, effective, quick, and safe, it should be used for congenital glaucoma evaluation. Experience and new drugs might, in the future, perfect a more effective procedure. For now, we recom mend our method of anesthesia and applana tion tonometry for intraocular pressure mea surements in infants. The exactness of the procedure eliminates the uncertainties pres ently attending anesthesia in infants.
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Our study showed that the intraocular pressure by applanation tonometry is lower in infants than in adults. However, it also showed that variations are wide and fre quent. Standardized anesthesia will reduce these variations to a minimum. Without it, one must accept these wide variations as nor mal. Group 4 clearly demonstrates this. Ap planation tonometry recorded pressure as low as 5 mm Hg and as high as 23 mm Hg in normal eyes. We performed tonometry in Group 4 as the practicing ophthalmologist would be likely to perform it. Experts using indentation tonometry found normal pressures over 20 mm Hg 1 ' 2 ' 4 ' 11 in infants. Some even eliminated from their study infants under the age of 5 months be cause the measurements were constantly under three divisions of the Schiotz tonom eter.3 Applanation tonometry also gave read ing of 20 mm Hg and over.6'7'9 Groups 1-6 in our study showed some examples of this. If anesthetic procedures are not stan dardized, one must presently accept wide variations in intraocular pressure measure ments in normal infants, as they have been accepted in the past (Table 1). With the standardized anesthesia proce dure, Group 8 showed an arithmetic mean of 9.56 mm Hg with a standard deviation of 2.66, giving confidence limits of ± 7.31 mm Hg for 99% of the population. This would make 16.87 mm Hg the border line between normal intraocular pressure and congenital glaucoma. If we applied Student's f-test to distribution, taking into account the number of infants and not the number of eyes, the confidence limits would be slight ly over 17 mm Hg for 99% of the popula tion. Sampaolesi, Reca, and Carro 8 found a low variation (SD 1.01) in 48 eyes of in fants, most of whom were over 1 year old. Other authors 5 ' 8 found a standard deviation in between that of Sampaolesi, Reca, and Carro and our own figures. Clinical experience is necessary before one can fully accept a valid intraocular pres sure border line for congenital glaucoma.
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With a standardized anesthesia procedure and applanation tonometry, we suggest that an intraocular pressure over 17 mm Hg is border line and that measurements of 20 mm Hg and over are glaucomatous. To avoid further damage to the eye, surgery should be performed when symptoms, such as pho tophobia and lacrimation, accompany pres sures of 20 mm Hg and higher. When the intraocular pressure is between 17 and 20 mm Hg, the infant should under go periodic measurement of the intraocular pressure under standardized anesthesia; if such figures persist, the corneal diameters, the eye volume (echogram), and the study of the optic disk will support the clinical decision. Standardized procedures are used in many clinical tests—adaptation curves, electroretinography, visual fields," and so forth. To yield meaningful results, intraocular pressure measurement in infants demands standard ization. A rise in venous pressure or in extraocular muscle tonus can vary the intra ocular pressure sharply. As a consequence, the intraocular pressure changes constantly in infants. Basal intraocular pressure sup plies the only steady-state for valid compari son. SUMMARY
We measured the intraocular pressure with manual applanation tonometers in 408 eyes of normal infants under general anes thesia. Various anesthesia procedures gave different results. Even with the same type of anesthesia, the higher and lower limits of intraocular pressure varied greatly. Since the level of the intraocular pressure appears to depend primarily on the level of relaxa tion in the infant we recommend applanation tonometry with a standardized anesthesia procedure to obtain the basal intraocular pressure. Using our method to measure the intraocular pressure in 30 normal eyes, we obtained a mean of 9.56 mm Hg with a standard deviation of 2.66. This result sug gested that an applanation measurement of
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17 mm Hg be considered the upper limit of normal pressure and that one of 20 mm Hg be considered the lower limit of pathologic pressure. Readings in between these two limits should be considered suspicious. ACKNOWLEDGMENTS
We thank the personnel of the Pediatric Services of the Cruz Roja, Nino Jesus, La Paz, and Fran cisco Franco Hospitals for cooperation and as sistance. REFERENCES
1. Barkan, O.: Surgery of congenital glaucoma. Am. J. Ophthalmol. 36:1523, 1953. 2. Apt, L.: Tonography in infantile glaucoma. Am. J. Ophthalmol. 43:624, 1957. 3. Ytteborg, J.: Investigations of the rigidity coefficient in children's eyes. Acta Ophthalmol. 38:658,1960. 4. Kornblueth, W., Abrahamov, A., Aladjemoff,
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L., Magora, F., and Gombos, G.: Intraocular pres sure in the newborn measured under general anes thesia. Arch. Ophthalmol. 67:750, 1962. 5. Manzitti, E., and Darnel, A.: Valores de la tonometria aplanatica en el lactante normal. Arch. Oftalmol. B. Aires 39:360, 1964. 6. Sampaolesi, R., Reca, R. M., and Carro, A.: Presion ocular en el nino hasta los 5 anos. Arch. Oftalmol. B. Aires 42:180, 1967. 7. Hetherington, J., and Shaffer, R. N.: Tonometry and tonography in congenital glaucoma. In vest. Ophthalmol. 7:134, 1968. 8. Carvalho, C. A., and Calixto, N.: Semilogia do glaucoma congenito. Rev. Bras. Oftalmol. 29:7, 1970. 9. Chandler, P. A., and Grant, W. M.: Lectures in Glaucoma. Philadelphia, Lea and Febiger, 1965, p. 301. 10. Kornblueth, W., Aladjemoff, L., Magora, F., and Gabbay, A.: Influence of general anesthesia on intraocular pressure in man. Arch. Ophthalmol. 61:84, 1959. 11. Scheie, H.: Management of infantile glau coma. Arch. Ophthalmol. 62:35, 1959.