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Intraocular Pressure Changes During Hemodialysis
INTRAOCULAR PRESSURE CHANGES DURING HEMODIALYSIS J O H N T. RAMSELL, M.D., P H I L I P P. ELLIS, M.D., CHRISTOPHER A. PATERSON, P H . D .
AND
Denver, Colorado
Increased intraocular pressure ( I O P ) has been observed during hemodialysis in uremic dogs and in uremic patients.1"6 It also has been suggested that since tonometry is effec tive in detecting IOP changes due to fluid transfer across the blood-aqueous barrier during dialysis, increases in I O P may paral lel and thus predict fluid movement across the blood barrier as in the development of cerebral edema during dialysis.1'3 This study was undertaken to further evaluate changes in IOP with hemodialysis and to determine whether a correlation exists between hourly changes in serum osmolality and IOP. METHODS
Twenty patients receiving chronic inter mittent hemodialysis were studied. All dyalyses were performed using the Kolff twincoil unit with Ultra-flo 145 (Travenol Labo ratories, Inc.) coils. The purpose of dialysis was to remove excess fluid weight as well as excess chemical constituents, such as urea nitrogen and creatinine. Intraocular pres sures were measured with a Tonair applanation tonometer. This instrument was demon strated to give comparable readings to the Goldmann applanation tonometer on 50 con secutive patients in the University of Colo rado eye clinic. Measurements were made, with the patient in supine position, on both eyes of each patient before dialysis, every hour during dialysis and at the conclusion of dialysis. Since the readings for both eyes From the Division of Ophthalmology, University of Colorado Medical Center, Denver, Colorado. This study was supported in part by an unrestricted grant from Research to Prevent Blindness, Inc., and also by Public Health Service Grant NB 05367-09 VSN. Reprint requests to Phillip P. Ellis, M.D., Divi sion of Ophthalmology, University of Colorado Medical Center, 4200 East Ninth Avenue, Denver, Colorado 80220.
were similar in almost every instance the mean value of the two eyes was determined for data analysis. When IOP readings were 25 mm Hg or more, a series of readings were taken and the recorded values were based upon the higher readings as recom mended by Posner and Inglima in their eval uation of the Tonair Applanometer.7 The duration of the dialysis was six hours in nine patients and five hours in 10 patients. In one patient, the dialysis had to be termi nated at three hours following a convulsion; this patient was dropped from the study. Arterial blood samples were collected for determination of serum osmolality (freezing point depression method, using an Advanced Osmometer) each time tonometry was per formed. Specimens were allowed to clot, were centrifuged, and the individual serum samples stored at 4°C until osmolality de terminations were performed. After collection and analysis of the IOP and serum osmolality data it was suggested that tonographic data may be of use in the interpretation of the findings. Unfortu nately, when the tonographic study was un dertaken only three of the original group of subjects were available for study; the others were deceased, had moved from the area or were transplant recipients. Therefore, four additional subjects were admitted to the to nographic study. Tonographic recordings (and Tonair measurements) were made just before dialysis and at the four-hour stage during dialysis. The mean value of tono graphic data from the two eyes was used for analysis. RESULTS
All patients in this study exhibited a de crease in body weight at the conclusion of dialysis. The mean initial serum osmolality was 311
926
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PRESSURE CHANGES IN HEMODIALYSIS
927
TABLE 1 INITIAL AND FINAL VALUES OF IOP AND SERUM OSMOLALITY Six-Hour Group (9 patients)
Five-Hour Group (10 patients) OsmolaHty (mOsm/L): Initial
311 (291, 331)*
313 (299, 331)*
312 (291, 331)*
282 (267, 303)
282 (273, 290)
282 (267, 331)
-29.5 (-24, -43)
-31.1 (-12, -42)
-31 (-12, -43)
20.4 (15.5,32.5)
20.6 (15,28)
20.5 (15,32.5)
18.9 (12,31)
22.7 (16,32.5)
20.7 (15,32.5)
-1.45 ( - 5 , +8)
+2.06 ( - 5 , +9.5)
-0.2 ( - 5 , +9.5)
Final Mean change IOP ( m m H g ) : Initial
Combined Groups
Final Mean change
* The numbers in parentheses refer to the range of values.
mOsm/L (range 291-331) and 313 mOsm/L and 20.6 (15-28) respectively. The five-hour (299-331) in the patients dialyzed five and group exhibited a mean change in I O P of six hours, respectively. The mean starting —1.45 with a range of —5 to + 8 . That in osmolality for all 19 patients was 312 the six-hour group was +2.05 with a range mOsm/L. Serum osmolality decreased during of —5 to +9.5. Combining the five- and sixdialysis in every patient. The change between hour groups we find only a 0.2 mm Hg ininitial and final osmolality in the five-hour crease in I O P at the conclusion of dialysis group was —29.5 mOsm/L (12-42) and that (Table 1). in the six-hour group was —31.1 mOsm/L Despite the lack of significance between (12-42). These figures are presented in initial and final IOP, careful analysis of Table 1. I O P changes during dialysis revealed some The predialysis IOP of all 19 patients interesting points. The changes are preranged from 15-32.5 mm Hg with a mean of sented in Table 2 and Figure 1. For conve20.4. The mean initial IOP and range for the nience all 19 patients are grouped together five- and six-hour group was 20.4 (15.5-32.5) for I O P and osmolality values between zero TABLE 2 MEAN IOP AND SERUM OSMOLALITY AT HOURLY INTERVALS DURING DIALYSIS*
Initial
One-Hour
Two-Hour
Three-Hour
Four-Hour
Five-Hour
Six-Hour
IOP (mm Hg)
20.5 ±1.0
20.1 ±1.4
19.2 ±1.1
21.1 ±1.3
21.1 ±1.2
21.3 ±1.4
22.7 ±1.8
Osmolality (mOsm/L)
313 ±2.5
305 ±2.4
299 ±2.3
294 ±2.2
289 ±2.1
284 ±2.0
282 ±2.0
* Values are arithmetic mean, ± standard error of the mean. Up to and including five hours, each group contains 19 patients. The six-hour group has only nine patients.
AMERICAN JOURNAL OF OPHTHALMOLOGY
928
and five hours. It can be seen that a signifi cant decrease in IOP occurred during the first two hours (from 20.4 to 19.0 mm Hg, p < . 0 5 ) . The increase in IOP between two and three hours (19.0 to 20.9 mm Hg) was significant at the 99% level. However, the IOP from three to six hours was not signifi cantly different from the baseline value. The apparent marked increase at six hours is due to the smaller number of observations since only nine patients were dialyzed a full six hours. These IOP changes are not, however, considered clinically significant. When the I O P changes in individual sub jects are considered, marked alterations are evident. In 10 of the 19 patients there was a
NOVEMBER, 1971
maximum rise in I O P ranging from 0.5 to 16 mm Hg, with a mean of 6.9 mm Hg. This increase occurred from one to six hours af ter dialysis was started. The remaining nine patients exhibited either no significant change or a sustained reduction in IOP dur ing dialysis. When the mean IOP changes of the entire group are considered only with re spect to time, individual elevated pressures are masked. The mean value of outflow facility ob tained by tonography before dialysis was 0.22 ± .026 (S.E.) and that after four hours was 0.21 ± .027. The I O P values for this smaller group of subjects exhibited a similar main tained elevation at four hours as was ob-
+ 10«
o to
O Q Z < Q.
o o
z
< x
— 10-
HOURS Fig. 1 (Ramsell, Ellis, and Paterson). Changes in IOP and serum osmolality with respect to time during dialysis. Percent change was calculated from the figures in Table 2. It should be noted that the six-hour points are the mean values from only nine patients; the other points are obtained from 19 patients (see text).
VOL. 72, NO. S
PRESSURE CHANGES IN HEMODIALYSIS
served in the original 19 subjects; the mean IOP before dialysis was 20.5 ± 1.03 and 24.6 ± 1.60 after four hours of dialysis. The patients exhibiting abnormally high IOP readings in this study were found to have normal applanation tensions, visual fields, and gonioscopic findings when exam ined in the eye clinic on a day when they were not undergoing dialysis. DISCUSSION
In the study reported by Sitprija, Holmes and Ellis 1 from this Medical Center in 1964, there was a mean decrease in serum osmolality of 37.6 mOsm/L (range 3-72) after about six hours dialysis. This compares with a mean fall in serum osmolality of 31 mOsm / L (12-43; 5 and 6 hour groups combined), in the present study. Despite the use of smaller coils in this study, 1.45 m2 (Ultra-flo 145) as opposed to 1.9 m2 (Twin-coil 190, Travenol) used in the earlier study,1 the ob served changes in osmolality are obviously not significantly different. Sitprija and associates2 found an average increase in I O P of 41.8% of control values in uremic dogs following dialysis, and an average increase in I O P of 4 to 8 mm Hg in the majority of uremic patients during dialy sis. Watson and Greenwood3 reported an average rise in IOP of 8.1 mm Hg in six pa tients during 12 dialyses. Biagini and Gloria4 reported a mean increase in I O P of 16% during dialysis of uremic patients. Applemans and associates5 demonstrated an increase in IOP up to 10 mm Hg in 80% of patients undergoing renal dialysis. These studies sug gest a correlation between decrease in plasma osmolality and increase in I O P dur ing dialysis. Presumably an influx of fluid into the eye due to the difference in osmolal ity between plasma and intraocular fluids re sults in an increased IOP. In none of the previous studies however was data presented which correlated hourly serum osmolality changes with increases in IOP. The data ob tained in this study not only confirm that in dividual increases in I O P can occur during
929
dialysis but can also be analysed to compare hourly changes in I O P and serum osmolality. In Figure 1 the hourly percent of change in serum osmolality is plotted against the hourly percent of change in IOP. As de scribed in Results, an initial decrease in I O P is followed by an increase which persists up to six hours. The initial decrease in I O P might be related to decreased intravascular volume as well as to reduced anxiety in the pa tients as the procedure became more familiar. The initial weight loss in patients undergoing dialysis represents principally a reduction in intravascular volume.8 Marked decreases in I O P paralleling weight loss in dogs were ob served by Sitprija and associates.2 The in crease in I O P between two and three hours is felt to be due to an osmotic influx of water into the eye as a result of the relative hyperosmolality of intraocular fluids. During en suing hours it is presumed that the intraocu lar and intravascular fluids approach osmotic equilibrium. It had been suggested to us that the main tained elevation of I O P at three to four hours might be due to a decrease in outflow facility. For this reason tonographic mea surements were made before and after four hours of dialysis. The results, which demon strated no change in outflow facility, indicate that it is not a significant factor in explain ing I O P changes observed during hemodialysis. Changes in I O P during hemodialysis might be related to the hourly rate of serum osmolality change; a more rapid decrease in serum osmolality resulting in a more pro nounced I O P change. I O P in uremic dogs during hemodialysis remained unchanged or showed a minimal increase when the reduc tion in serum osmolality averaged 8.5 mOsm / L per hour. When the serum osmolality re duction averaged 11 mOsm/L per hour the I O P increased significantly.2 In the present study serum osmolality decreased at 5-7 mOsm/L per hour and mean I O P changes were not significant.
930
AMERICAN JOURNAL OF OPHTHALMOLOGY
Barry, Khoury, and Brooks9 found that, although changes in mean serum osmolality appear to be associated with reciprocal changes in IOP, the two are not closely re lated. Galin, Aizawa, and McLean10 consider that the water-drinking test, at its outset, de pends upon the level of induced hypo-osmolality, but add that in man the statistical cor relation between plasma hypo-osmolality and IOP increase is not adequate to make this an inviolate hypothesis. It should be recalled that in the present study marked increases in IOP during hemodialysis did occur at various times in 10 of the 19 patients, but the times did not cor relate with any particular stage of serum os molality reduction. The possibility exists that the degree and timing of IOP increases dur ing hemodialysis depends principally upon the extent of changes in intravascular vol ume. In those patients exhibiting the greatest IOP increase during dialysis the initial fall in IOP (Fig. 1), which is considered to cor relate with weight changes, was minimal. It can be concluded that during hemodial ysis IOP is affected by factors other than a relative reduction in serum osmolality. Krupin, Podos, and Becker11 have suggested that the ocular hypotensive response to hyperosmotic agents might be mediated, in part, by mechanisms in the central nervous system. SUMMARY
In 19 uremic patients undergoing hemo dialysis the mean final I O P was only 0.2 mm Hg above the mean initial values. However, in 10 of the 19 patients maximum increases in IOP ranging from 0.5 to 16 mm Hg oc curred at times ranging from one to six hours. Statistically, but not clinically signifi
NOVEMBER, 1971
cant mean IOP changes were observed dur ing the early stages of dialysis and are dis cussed. Serum osmolality decreased in all pa tients; the mean decrease was 31 mOsm/L. Hourly IOP changes did not correlate with reduction in serum osmolality. The influence of changes in intravascular volume on IOP during hemodialysis is discussed. ACKNOWLEDGMENT
We acknowledge the cooperation of members of the Renal Division during this study. REFERENCES
1. Sitprija, V., Holmes, J. H., and Ellis, P. P.: Intraocular pressure changes during artificial kid ney therapy. Arch. Ophth. 72:626, 1964. 2. Sitprija, V., Holmes, J. H , and Ellis, P. P.: Changes in intraocular pressure during hemodialy sis. Invest. Ophth. 3 :273, 1964. 3. Watson, S. G., and Greenwood, W. R.: Stud ies on the intraocular pressure during hemodialysis. Canad. J. Ophth. 1:301, 1966. 4. Biagini, M., and Gloria, E. M.: Comportamento della pressione intraoculare durante emodialisi in pazienti affectti da uremia cronica. Ann. Otal. 93 :705, 1967. 5. Applemans, M., Dernouchamps, J. P., DeWolf, J., and Dralands, L.: Evolution de la tension oculaire durant la dialyse renale. Bull. Soc. Belg. Ophth. 147:426, 1967. 6. Sevvik, J., and Danko, M.: Hydrodynamika komorovej vody u klinickych acidoz. Cesk. Oftal. 24:80, 1968. 7. Posner, A., and Inglima, R.: Evaluation of Tonair tonometer vs Schiotz tonometer and applanometer. EENT Monthly 47:469, 1968. 8. Del Greco, F., Shere, J., and Simon, N. M.: Hemodynamic effects of hemodialysis in chronic re nal failure. Tr. Am. Soc. Artif. Int. Organs 10:353, 1964. 9. Barry, K. G., Khoury, A. H., and Brooks, M. H.: Mannitol and isosorbide. Arch. Ophth. 81: 695, 1969. 10. Galin, J. A., Aizawa, F., and McLean, J. M.: Hemodilution and intraocular pressure. Arch. Ophth. 73:2S, 1965. 11. Krupin, T., Podos, S. M., Becker, B.: Effect of optic nerve transection on osmotic alterations of intraocular pressure. Am. J. Ophth. 70:214, 1970.
AND
Denver, Colorado
Increased intraocular pressure ( I O P ) has been observed during hemodialysis in uremic dogs and in uremic patients.1"6 It also has been suggested that since tonometry is effec tive in detecting IOP changes due to fluid transfer across the blood-aqueous barrier during dialysis, increases in I O P may paral lel and thus predict fluid movement across the blood barrier as in the development of cerebral edema during dialysis.1'3 This study was undertaken to further evaluate changes in IOP with hemodialysis and to determine whether a correlation exists between hourly changes in serum osmolality and IOP. METHODS
Twenty patients receiving chronic inter mittent hemodialysis were studied. All dyalyses were performed using the Kolff twincoil unit with Ultra-flo 145 (Travenol Labo ratories, Inc.) coils. The purpose of dialysis was to remove excess fluid weight as well as excess chemical constituents, such as urea nitrogen and creatinine. Intraocular pres sures were measured with a Tonair applanation tonometer. This instrument was demon strated to give comparable readings to the Goldmann applanation tonometer on 50 con secutive patients in the University of Colo rado eye clinic. Measurements were made, with the patient in supine position, on both eyes of each patient before dialysis, every hour during dialysis and at the conclusion of dialysis. Since the readings for both eyes From the Division of Ophthalmology, University of Colorado Medical Center, Denver, Colorado. This study was supported in part by an unrestricted grant from Research to Prevent Blindness, Inc., and also by Public Health Service Grant NB 05367-09 VSN. Reprint requests to Phillip P. Ellis, M.D., Divi sion of Ophthalmology, University of Colorado Medical Center, 4200 East Ninth Avenue, Denver, Colorado 80220.
were similar in almost every instance the mean value of the two eyes was determined for data analysis. When IOP readings were 25 mm Hg or more, a series of readings were taken and the recorded values were based upon the higher readings as recom mended by Posner and Inglima in their eval uation of the Tonair Applanometer.7 The duration of the dialysis was six hours in nine patients and five hours in 10 patients. In one patient, the dialysis had to be termi nated at three hours following a convulsion; this patient was dropped from the study. Arterial blood samples were collected for determination of serum osmolality (freezing point depression method, using an Advanced Osmometer) each time tonometry was per formed. Specimens were allowed to clot, were centrifuged, and the individual serum samples stored at 4°C until osmolality de terminations were performed. After collection and analysis of the IOP and serum osmolality data it was suggested that tonographic data may be of use in the interpretation of the findings. Unfortu nately, when the tonographic study was un dertaken only three of the original group of subjects were available for study; the others were deceased, had moved from the area or were transplant recipients. Therefore, four additional subjects were admitted to the to nographic study. Tonographic recordings (and Tonair measurements) were made just before dialysis and at the four-hour stage during dialysis. The mean value of tono graphic data from the two eyes was used for analysis. RESULTS
All patients in this study exhibited a de crease in body weight at the conclusion of dialysis. The mean initial serum osmolality was 311
926
VOL. 72, NO. S
PRESSURE CHANGES IN HEMODIALYSIS
927
TABLE 1 INITIAL AND FINAL VALUES OF IOP AND SERUM OSMOLALITY Six-Hour Group (9 patients)
Five-Hour Group (10 patients) OsmolaHty (mOsm/L): Initial
311 (291, 331)*
313 (299, 331)*
312 (291, 331)*
282 (267, 303)
282 (273, 290)
282 (267, 331)
-29.5 (-24, -43)
-31.1 (-12, -42)
-31 (-12, -43)
20.4 (15.5,32.5)
20.6 (15,28)
20.5 (15,32.5)
18.9 (12,31)
22.7 (16,32.5)
20.7 (15,32.5)
-1.45 ( - 5 , +8)
+2.06 ( - 5 , +9.5)
-0.2 ( - 5 , +9.5)
Final Mean change IOP ( m m H g ) : Initial
Combined Groups
Final Mean change
* The numbers in parentheses refer to the range of values.
mOsm/L (range 291-331) and 313 mOsm/L and 20.6 (15-28) respectively. The five-hour (299-331) in the patients dialyzed five and group exhibited a mean change in I O P of six hours, respectively. The mean starting —1.45 with a range of —5 to + 8 . That in osmolality for all 19 patients was 312 the six-hour group was +2.05 with a range mOsm/L. Serum osmolality decreased during of —5 to +9.5. Combining the five- and sixdialysis in every patient. The change between hour groups we find only a 0.2 mm Hg ininitial and final osmolality in the five-hour crease in I O P at the conclusion of dialysis group was —29.5 mOsm/L (12-42) and that (Table 1). in the six-hour group was —31.1 mOsm/L Despite the lack of significance between (12-42). These figures are presented in initial and final IOP, careful analysis of Table 1. I O P changes during dialysis revealed some The predialysis IOP of all 19 patients interesting points. The changes are preranged from 15-32.5 mm Hg with a mean of sented in Table 2 and Figure 1. For conve20.4. The mean initial IOP and range for the nience all 19 patients are grouped together five- and six-hour group was 20.4 (15.5-32.5) for I O P and osmolality values between zero TABLE 2 MEAN IOP AND SERUM OSMOLALITY AT HOURLY INTERVALS DURING DIALYSIS*
Initial
One-Hour
Two-Hour
Three-Hour
Four-Hour
Five-Hour
Six-Hour
IOP (mm Hg)
20.5 ±1.0
20.1 ±1.4
19.2 ±1.1
21.1 ±1.3
21.1 ±1.2
21.3 ±1.4
22.7 ±1.8
Osmolality (mOsm/L)
313 ±2.5
305 ±2.4
299 ±2.3
294 ±2.2
289 ±2.1
284 ±2.0
282 ±2.0
* Values are arithmetic mean, ± standard error of the mean. Up to and including five hours, each group contains 19 patients. The six-hour group has only nine patients.
AMERICAN JOURNAL OF OPHTHALMOLOGY
928
and five hours. It can be seen that a signifi cant decrease in IOP occurred during the first two hours (from 20.4 to 19.0 mm Hg, p < . 0 5 ) . The increase in IOP between two and three hours (19.0 to 20.9 mm Hg) was significant at the 99% level. However, the IOP from three to six hours was not signifi cantly different from the baseline value. The apparent marked increase at six hours is due to the smaller number of observations since only nine patients were dialyzed a full six hours. These IOP changes are not, however, considered clinically significant. When the I O P changes in individual sub jects are considered, marked alterations are evident. In 10 of the 19 patients there was a
NOVEMBER, 1971
maximum rise in I O P ranging from 0.5 to 16 mm Hg, with a mean of 6.9 mm Hg. This increase occurred from one to six hours af ter dialysis was started. The remaining nine patients exhibited either no significant change or a sustained reduction in IOP dur ing dialysis. When the mean IOP changes of the entire group are considered only with re spect to time, individual elevated pressures are masked. The mean value of outflow facility ob tained by tonography before dialysis was 0.22 ± .026 (S.E.) and that after four hours was 0.21 ± .027. The I O P values for this smaller group of subjects exhibited a similar main tained elevation at four hours as was ob-
+ 10«
o to
O Q Z < Q.
o o
z
< x
— 10-
HOURS Fig. 1 (Ramsell, Ellis, and Paterson). Changes in IOP and serum osmolality with respect to time during dialysis. Percent change was calculated from the figures in Table 2. It should be noted that the six-hour points are the mean values from only nine patients; the other points are obtained from 19 patients (see text).
VOL. 72, NO. S
PRESSURE CHANGES IN HEMODIALYSIS
served in the original 19 subjects; the mean IOP before dialysis was 20.5 ± 1.03 and 24.6 ± 1.60 after four hours of dialysis. The patients exhibiting abnormally high IOP readings in this study were found to have normal applanation tensions, visual fields, and gonioscopic findings when exam ined in the eye clinic on a day when they were not undergoing dialysis. DISCUSSION
In the study reported by Sitprija, Holmes and Ellis 1 from this Medical Center in 1964, there was a mean decrease in serum osmolality of 37.6 mOsm/L (range 3-72) after about six hours dialysis. This compares with a mean fall in serum osmolality of 31 mOsm / L (12-43; 5 and 6 hour groups combined), in the present study. Despite the use of smaller coils in this study, 1.45 m2 (Ultra-flo 145) as opposed to 1.9 m2 (Twin-coil 190, Travenol) used in the earlier study,1 the ob served changes in osmolality are obviously not significantly different. Sitprija and associates2 found an average increase in I O P of 41.8% of control values in uremic dogs following dialysis, and an average increase in I O P of 4 to 8 mm Hg in the majority of uremic patients during dialy sis. Watson and Greenwood3 reported an average rise in IOP of 8.1 mm Hg in six pa tients during 12 dialyses. Biagini and Gloria4 reported a mean increase in I O P of 16% during dialysis of uremic patients. Applemans and associates5 demonstrated an increase in IOP up to 10 mm Hg in 80% of patients undergoing renal dialysis. These studies sug gest a correlation between decrease in plasma osmolality and increase in I O P dur ing dialysis. Presumably an influx of fluid into the eye due to the difference in osmolal ity between plasma and intraocular fluids re sults in an increased IOP. In none of the previous studies however was data presented which correlated hourly serum osmolality changes with increases in IOP. The data ob tained in this study not only confirm that in dividual increases in I O P can occur during
929
dialysis but can also be analysed to compare hourly changes in I O P and serum osmolality. In Figure 1 the hourly percent of change in serum osmolality is plotted against the hourly percent of change in IOP. As de scribed in Results, an initial decrease in I O P is followed by an increase which persists up to six hours. The initial decrease in I O P might be related to decreased intravascular volume as well as to reduced anxiety in the pa tients as the procedure became more familiar. The initial weight loss in patients undergoing dialysis represents principally a reduction in intravascular volume.8 Marked decreases in I O P paralleling weight loss in dogs were ob served by Sitprija and associates.2 The in crease in I O P between two and three hours is felt to be due to an osmotic influx of water into the eye as a result of the relative hyperosmolality of intraocular fluids. During en suing hours it is presumed that the intraocu lar and intravascular fluids approach osmotic equilibrium. It had been suggested to us that the main tained elevation of I O P at three to four hours might be due to a decrease in outflow facility. For this reason tonographic mea surements were made before and after four hours of dialysis. The results, which demon strated no change in outflow facility, indicate that it is not a significant factor in explain ing I O P changes observed during hemodialysis. Changes in I O P during hemodialysis might be related to the hourly rate of serum osmolality change; a more rapid decrease in serum osmolality resulting in a more pro nounced I O P change. I O P in uremic dogs during hemodialysis remained unchanged or showed a minimal increase when the reduc tion in serum osmolality averaged 8.5 mOsm / L per hour. When the serum osmolality re duction averaged 11 mOsm/L per hour the I O P increased significantly.2 In the present study serum osmolality decreased at 5-7 mOsm/L per hour and mean I O P changes were not significant.
930
AMERICAN JOURNAL OF OPHTHALMOLOGY
Barry, Khoury, and Brooks9 found that, although changes in mean serum osmolality appear to be associated with reciprocal changes in IOP, the two are not closely re lated. Galin, Aizawa, and McLean10 consider that the water-drinking test, at its outset, de pends upon the level of induced hypo-osmolality, but add that in man the statistical cor relation between plasma hypo-osmolality and IOP increase is not adequate to make this an inviolate hypothesis. It should be recalled that in the present study marked increases in IOP during hemodialysis did occur at various times in 10 of the 19 patients, but the times did not cor relate with any particular stage of serum os molality reduction. The possibility exists that the degree and timing of IOP increases dur ing hemodialysis depends principally upon the extent of changes in intravascular vol ume. In those patients exhibiting the greatest IOP increase during dialysis the initial fall in IOP (Fig. 1), which is considered to cor relate with weight changes, was minimal. It can be concluded that during hemodial ysis IOP is affected by factors other than a relative reduction in serum osmolality. Krupin, Podos, and Becker11 have suggested that the ocular hypotensive response to hyperosmotic agents might be mediated, in part, by mechanisms in the central nervous system. SUMMARY
In 19 uremic patients undergoing hemo dialysis the mean final I O P was only 0.2 mm Hg above the mean initial values. However, in 10 of the 19 patients maximum increases in IOP ranging from 0.5 to 16 mm Hg oc curred at times ranging from one to six hours. Statistically, but not clinically signifi
NOVEMBER, 1971
cant mean IOP changes were observed dur ing the early stages of dialysis and are dis cussed. Serum osmolality decreased in all pa tients; the mean decrease was 31 mOsm/L. Hourly IOP changes did not correlate with reduction in serum osmolality. The influence of changes in intravascular volume on IOP during hemodialysis is discussed. ACKNOWLEDGMENT
We acknowledge the cooperation of members of the Renal Division during this study. REFERENCES
1. Sitprija, V., Holmes, J. H., and Ellis, P. P.: Intraocular pressure changes during artificial kid ney therapy. Arch. Ophth. 72:626, 1964. 2. Sitprija, V., Holmes, J. H , and Ellis, P. P.: Changes in intraocular pressure during hemodialy sis. Invest. Ophth. 3 :273, 1964. 3. Watson, S. G., and Greenwood, W. R.: Stud ies on the intraocular pressure during hemodialysis. Canad. J. Ophth. 1:301, 1966. 4. Biagini, M., and Gloria, E. M.: Comportamento della pressione intraoculare durante emodialisi in pazienti affectti da uremia cronica. Ann. Otal. 93 :705, 1967. 5. Applemans, M., Dernouchamps, J. P., DeWolf, J., and Dralands, L.: Evolution de la tension oculaire durant la dialyse renale. Bull. Soc. Belg. Ophth. 147:426, 1967. 6. Sevvik, J., and Danko, M.: Hydrodynamika komorovej vody u klinickych acidoz. Cesk. Oftal. 24:80, 1968. 7. Posner, A., and Inglima, R.: Evaluation of Tonair tonometer vs Schiotz tonometer and applanometer. EENT Monthly 47:469, 1968. 8. Del Greco, F., Shere, J., and Simon, N. M.: Hemodynamic effects of hemodialysis in chronic re nal failure. Tr. Am. Soc. Artif. Int. Organs 10:353, 1964. 9. Barry, K. G., Khoury, A. H., and Brooks, M. H.: Mannitol and isosorbide. Arch. Ophth. 81: 695, 1969. 10. Galin, J. A., Aizawa, F., and McLean, J. M.: Hemodilution and intraocular pressure. Arch. Ophth. 73:2S, 1965. 11. Krupin, T., Podos, S. M., Becker, B.: Effect of optic nerve transection on osmotic alterations of intraocular pressure. Am. J. Ophth. 70:214, 1970.