|Year : 1971 | Volume
| Issue : 4 | Page : 159-163
Ocular changes following cataract extraction : Effect on intra-ocular pressure and rate of aqueous formation
K Nath, RL Vaid
Aligarh Muslim University Institute of Ophthalmology and Jawaharlal Nehru Medical. College, Aligarh, India
Aligarh Muslim University Institute of Ophthalmology and Jawaharlal Nehru Medical. College, Aligarh
Source of Support: None, Conflict of Interest: None
|How to cite this article:|
Nath K, Vaid R L. Ocular changes following cataract extraction : Effect on intra-ocular pressure and rate of aqueous formation. Indian J Ophthalmol 1971;19:159-63
|How to cite this URL:|
Nath K, Vaid R L. Ocular changes following cataract extraction : Effect on intra-ocular pressure and rate of aqueous formation. Indian J Ophthalmol [serial online] 1971 [cited 2020 May 28];19:159-63. Available from: http://www.ijo.in/text.asp?1971/19/4/159/35006
A variable degree of hypotony exists for 6 weeks to 15 months after an uncomplicated cataract extraction. On the other hand, Miller. Kesku and Becker  and Lee and Trotter  have reported a decrease in the facility of outflow of aqueous. Hypotony and decrease in the facility of outflow which appears paradoxical was explained by Miller et al  on the basis of hyposecretion of aqueous humour. This study was undertaken to assess the effect of uncomplicated cataract extraction on the intraocular pressure and to correlate the results with the rate of aqueous formation, so as to establish the cause of change in the intraocular pressure and confirm the observations made by Miller et al  The effect of different modes of cataract extraction and types of iridectomies on the intraocular pressure and rate of aqueous formation were also studied.
| Material and Methods|| |
In 33 cases with uncomplicated senile cataracts included in the present study, the applanation intraocular pressure was recorded and cases with a pressure higher than 20 mm. Hg. were excluded. Slit lamp and gonioscopic examinations were carried out in each case.
Rate of aqueous formation was calculated by using the equation: F = C (Po - Pev). where:
F = Rate of acqueous formation expressed as microlitres per minute; I
Po=Original intraocular pressure (applanation);
C=Facility of outflow - from tonographic method; and
Pev = Episcleral venous pressure - (10 mm,; Hg. was taken as an average value).
In each case the first 4 minute tonogram was obtained and facility of outflow (C) calculated by using 1955 Friedenwald nomogram. Episcleral venous pressure has been measured by a number of observers and there is general agreement that it usually lies in the range of 8-12 Hg. (Gloster  ; Lieth  ; Linne; and Wigelin and Lohlein  ). In the present study the average episcleral venous pressure was taken to be 10 mm. Hg.
Preplanned cataract extractions were performed by the same surgeon and the same type of recoding with elimination of complicated cases was done as in the previous article.
After 6 to 12 weeks of cataract extraction intraocular pressure, tonography, slit lamp examination and gonioscopy were repeated. The rate of aqueous formation was again calculated in each case.
| Results|| |
In 33 eyes of 32 cases of senile cataracts, the pre-operative intraocular pressure ranged between 10 to 19 mm of Hg. with an average value of 14.5 mm Hg. Teh rate of aqueous formation varied from 0.45 to 3.60 ul/mt with an average value of 1.70 ul/mt
Post-operatively, the intra-ocular pressure in the same number of eyes varied from 9 to 17 mm. of Hg. with an average of 11.9 mm. a decrease from the preoperative value. It decreased in 24 eyes, increased in 1 and remained unchanged in 8.
The mean value of the rate of aqueous formation, 1.70 ul/mt, which varied post-operatively, from 0.22 to 2.80 ul/mt. the same group, fell by 0.93 ul/mt. (54.7%). [Table - 1] summarises all the findings.
The values were nearly similar after intra (21 eyes) or extracapsular (12 eyes) cataract extractions [Table - 2].
There was marked inhibition of aqueous formation in cases where a complete iridectomy was done (46 ul/mt.) as compared to the peripheral button hole iridectomy groups. The average decrease in aqueous formation following cataract extraction was 54.7%. The average fall was 44.1% in cases with peripheral iridectomy (22) and 72.9% with complete iridectomy (11 eyes) [Table - 3]). These values were independent of the mode of cataract extraction. In all the four eyes in which the rate of aqueous formation had increased, a peripheral button-hole iridectomy had been performed.
| Discussion|| |
Our findings are in close agreement with those of Hilding and Miller et al and show a fall in intraocular pressure and rate of aqueous formation. The average intraocular pressure in 33 eyes fell from 14.5 to 11.9 mm of Hg. after 6 to 12 weeks of surgery and was found statistically significant by paired `T' test, as the calculated value (5.5) is greater than the tabulated value (1.96) at 5% level of significance in 32 degrees of freedom.
This fall in intra-ocular tension was mainly due to decrease in the rate of aqueous formation as the average rate of aqueous formation in 33 eyes decreased from 1.70 ul/mt. to 0.77 ul/mt. and was also found to be statistically significant by paired `T' test as the calculated value (4.8) is greater than the tabulated value (1.96) at 5% of level of significance in 32 degrees of freedom.
The decrease in the rate of acqueous formation is not universal as is evident by the fact that the rate decreased in 26 eyes, remained unchanged in 3 and increased in 4 eyes but it does decrease in the great majority.
What are the various .likely factors which bring about. a sudden suppression in the amount of aqueous formation in the ciliary vasculature, is a question we are not in a position to answer at the moment. One of the various factors can be the sudden decompression of the anterior chamber bringing about a vasodilatation followed by a sudden sustained reflex vaso constriction of the vasculature in the ciliary processes. It is possible that this vasospasm is sustained due to inadequate build up in the pressure of aqueous humour from which a minimal leak may persist for a long time and thus this vasospasm only acts as a protective phenomenon to prevent the occurrence of haemorrhages in the ciliary process.
The mode of cataract extraction has nothing to do with the suppression of aqueous formation as the average difference in the postoperative value of the rate of aqueous formation was not significant [Table - 3]. The same argument also rules out any effect of the traction on the ciliary body due to the manipulation of lens in cases where intra-capsular extraction is performed.
On the other hand, trauma to the iris decreases the rate of aqueous formation to the extent of 44.1 % in cases where a peripheral iridectomy was done (22) against 72.9 per cent in cases of complete iridectomy (11). Here again the cause may be the reflex vasospasln due to trauma to the iris and ciliary body.
| Summary and Conclusion|| |
A tonometry and tonographic study on 33 eyes before and 6 to 12 weeks after cataract extraction shows a significant fall in the intraocular pressure. In the large majority, there was marked inhibition in the rate of aqueous formation and the average drop was 54.7%. The decrease in the rate of aqueous formation has nothing to do with the type of cataract extraction but was marked in cases where a large iridectomy was done. The probable cause lies in the reflex vasospasm of the ciliary vessels.
| References|| |
GLOSTER J.: Tonometery and Tonography (1st edition), p. 118, J. and A. Churchil Ltd., London (1966).
HILDING A. C.: Reduced ocular tension after cataract jurgery. A. M. A. Arch. Ophthal. (Chicago,) 53, 689: (1955).
LEE P. F. and TROTTER R. R.: Tonography and Gonioscopy before and after cataract extraction A. M. A. Arch. Ophthal. (Chicago), 58, 407-416: (1957).
LIETH A. B.: Episcleral venous pressure in tonography. Brit J. Ophthal., 47, 271-278: (1963).
LINNER E.: Acta Ophthal., Kbh 33, 101 (1955). Cited in 1, p. 118.
MILLER J. E., KESKY G. R and BECKER B.: Cataarct extraction and aqueous outflow. A.M.A. Arch.. Ophthal, (Chicago), 58, 401-406 (1957)
WEIGELIN E. and LOHLEIN H.: V. Graefes Arch. Ophthal. 153. 202: (1952).
[Table - 1], [Table - 2], [Table - 3]