|Year : 1971 | Volume
| Issue : 1 | Page : 7-13
Changes of refraction after cataract surgery
PA Lamba, NN Sood
Department of Ophthalmology, Jawaharlal Institute of Postgraduate Medical Education and Research, Pondicherry, India
P A Lamba
Department of Ophthalmology, Jawaharlal Institute of Postgraduate Medical Education and Research, Pondicherry
Source of Support: None, Conflict of Interest: None
|How to cite this article:|
Lamba P A, Sood N N. Changes of refraction after cataract surgery. Indian J Ophthalmol 1971;19:7-13
The obligation of the cataract surgeon towards his patient does not end just with a perfect surgical result. Early rehabilitation and prescription of glasses may be the answer to the adjustment in aphakia. In this country. due to socio-economic factors, early prescription of glasses to aphakics poses a special problem especially for the one eyed individual, a mature cataract in both eyes, or the only earning member of the family who has to undergo the surgical lens extraction.
Cataract incisions and their closures have been widely studied with an attempt to reduce overall astimatism, ,,, but there has been a paucity of studies regarding the astigmatic changes resulting from these techniques. Beasley  , Elenius and Karo  studied the post-operative changes in the refractive power of the cornea using a keratometer at varying periods. There are many factors which seem to influence the amount of astigmatism produced and these will be discussed on this paper. The study was designed to consider the changes in refraction at varying periods after cataract extraction with an attempt to correlate the findings so that accurate predictions relative to refraction changes may be male.
| Methods and Material|| |
An evaluation of 100 cataract extractions (intra-capsular) performed during early 1969 at the Department of Ophthalmology, JIPMER Hospital is attempted. To avoid personal factors the operations performed by either of us are included. Either of the following techniques was used for incision and wound closure.
1. A 3 mm. conjunctival flap is reflected over the limbos. The flap is dissected into the cornea which is split for 1 to 2 mm. with a Took's knife. Haemostasis is obtained by heat cautery. A limbal gutter is prepared by incising partially through the thickness of the cornea using the tip of a Bard Parker knife without entering the anterior chamber. Using Mendoza's technique  as a basis, one preplaced corneoscleral 6-0 silk suture is placed through the cut edges (entering the cornea near the base of conjunctival corneal flap) and across the gutter. The suture is pulled up to form a loop and a perpendicular ab extern incision is made into anterior chamber between the arms of the loop at the 12 o'clock position. The limbal wound is enlarged temporally and nasally using Castroviejo's corneal scissors, holding the scissors at right angles to the cornea to produce a perpendicular incision.
2. The classical limbal incision using Von Graefe's cataract knife and enlarged with scissors. The corneal incision was not made by either of us.
The number of sutures used varied from one to three corneoscleral sutures supplemented by conjunctival sutures. In 16 cases, only one corneoscleral suture was introduced while in 54 cases two or more sutures were applied. Peripheral, complete or no iridecomy was Anna in this series.
Post-operatively all these patients were regularly examined and refracted at weekly intervals starting from 8th day to 4~ days. At each follow up visit, the refraction was done and the retinoscopic findings were noted down correct to 0.5 diopter. A record was also kept of the maximal visual acuity with glasses at the time of the visit The changes in the dioptrie power, the degree, and axis of astigmatism have been studied in relation to type of section, number of corneoscleral sutures and changes due to prolapse of vitreous.
Changes in Axis
An analysis of the axis of postoperative astigmatism at varying periods after surgery is shown in [Table - 1]. On the 8th day, 77 percent of eyes had astigmatism against the rule (greater curvature horizontal) while 18 per cent had astigmatism with-the-rule (greater curvature vertical). Only five eyes were seen to be without astigmatism. With the passage of time (48 days after operation) 27 per cent eyes were seen to be with no astigmatism and the individuals showing astigmatism with-the-rule and against-the-rule showed a decline. Only 6 eyes had astigmatism with-the-rule and in contrast 67 per cent had astigmatism against-the-rule. This change is believed to be due to the healing of limbal wound and contraction of the scar.
Changes in Spherical Refraction :
(Less Corneal Curvature)
[Table - 2] shows the changes of -refraction in the post-operative period as seen along the lesser corneal curvature. 83 per cent of the individuals showed refraction between +10.5 to +13.0 diopters at the 48th post-operative day. The mean values of spherical refraction [Table - 4] on the 8th and 48th post-operative day had been +11.06 and +11.59 diopters. This change (0.53 D increase) has been gradual as illustrated. The final mean spherical power observed was +11.59 diopters with a standard deviation of + 1.05.
Changes in Astigmatism:
(Difference between greater and lesser corneal curvature).
[Table - 3] reveals that at the examination on 48th post-operative day, 27 per cent of individuals were seen to be without any difference between greater and lesser corneal curvatures. 70 per cent of the individuals in the series exhibited a residual astigmatic error of +1.0 D or less. Maximal astigmatism (+ 5.5 diopter or above) was observed only in 7 per cent cases on 8th post-operative day and 5 per cent on the 16th postoperative day. Maximal astigmatism recorded after 48th post-operative day was 4 diopters observed in one case only. Mean values of astigmatism showed a progressive decrease with the passage of time in the post-operative period. It becomes almost stationary at 40th post-operative day signifying the firm closure of the wound.
An important fact which was observed and well documented in [Table - 4] is that with the passage of time the dioptric power along the lesser curvature of the cornea tended to increase while it was opposite along the greater curvature. The net result of the change was a decrease in the degree of astigmatism. The mean manifested astigmatism at the 48th post-operative day was +0.93 diopter with a standard deviation of ± 0.85. It showed a change of 1.49 diopters compared to the mean astigmatic value at the 8th post-operative day.
| Discussion|| |
Comprehensive cataract management rests atop a tripod of interrelated objectives; good surgery, adequate correction of aphakia, and timely visual rehabilitation. The first objective has been adequately achieved through the recent advances in incision and wound closure using an operating microscope. The latter two objectives are receiving an increasing attention by ophthalmologists.
The incision for cataract extraction causes a corneal distortion that gradually reduces as the healing occurs. Duke Elder  in his encyclopaedic work observed an astigmatism of 8-10 diopters on 20th post-operative day, decreasing to an average of 2-3 diopters on 40th day. The post-operative keratometric readings are valuable for the estimation of astigmatism since it is entirely corneal. The limitations of the use of this instrument are evident from the following facts.
(a) The use of keratometer is of considerable scientific value but it saves the time only at the cost of accuracy (Duke Elder).
(b) Since the nodal point of an aphakic eye has moved forward the optical effect of the corneal curvature is never so strong as is indicated by direct measurement with ophthalmometer. Beasley  also observed that the keratometric measurements err on the low side when small amounts of astigmatism are present but err on the high side as the astigmatism increases.
Various workers have reported a decline in the post-operative astigmatism by the use of multiple sutures (Taylor  , Scheiel  ). Hilding  observed that average astigmatism following the use of two sutures was +1.9 diopters but when 4 sutures were used it was reduced to 1.6 diopters. Nirankari and Khanna  . observed a high degree of corneal astigmatism (with an average of 7.242 D) on the 10th post-operative day, while in our series the mean value for the degree of astigmatism on 8th post-operative day with limbal section was 2.42 D (S.D. + 1.56 D). Beasley  in his series placed the section anterior to the Schwalbe's line and used 3 preplaced corneoscleral sutures. He recorded the average manifest astigmatism of 2.01 diopters (.3 diopters less than measured with keratometer) 46 days after cataract surgery. Elenius and Karo  studied the changes in the refractive power of cornea in 62 aphakic eyes using 5 corneo-scleral unremoved for one month and observed on an average astigmatism of 3.1 diopters at 3rd postoperative month. The average astigmatism seen at the end of 48 days in our series was 0.93 diopter (S.D. - 0.85 D) against-the-rule.
The relationship of iridectomy to the amount of post-operative astigmatism has been widely debated. In this series, we have observed that the post-operative astigmatism was relatively higher (average 0.6 diopters) when complete iridectomy was done as compared to the cases with or without peripheral iridectomy. The experience of Sloane was similar. No satisfactory explanation can be given for this phenomenon, however it is postulated that the forward movement of the vitreous close to the wound may have some role to play in wound healing. Out of 9 cases showing high grade astigmatism (more than 2.5 diopters) on 48th post-operative day, 5 cases were seen to be associated with varying degree of vitreous loss. The present observations reveal that the dioptric power of lesser curvature of cornea (horizontal axis) rises while the vertical dioptric power decreases in the post-operative period due to the flattening of the corneal curvature. We believe that the condition of suture astigmatism (Floyd  ) does not exist and that the post-operative changes in astigmatism are probably due to healing of the wound and contraction of scar resulting in flattening of the cornea in the vertical meridian. A similar view was also expressed by Nirankari
No appreciable difference in astigmatism was observed in cases with one or two conrneoscleral sutures when they were supplemented with a conjunctival flap. The conjunctival flap sutured firmly to the posterior lip of the conjunctiva and Tenon's flap gave an excellent secondary support to `the limbal wound These sutures are less likely to leak and they produce no suture tract for possible epithelialization. We are of the opinion that the number of stitches put is not of much importance so long as accurate and exact approximation is achieved. The technique of incision and wound closure followed in the present series ensured an alignment of suture, good opposition of the perpendicular limbal incision and fulfilled all the criteria of evaluation described by McLean  .
From the present study it has been observed that the spherical refraction and the astigmatism showed a progressive rise and decline respectively till 40th postoperative day after which the curve became horizontal (illustrated [Figure - 1]). The linear graph represented settling down of refraction to its permanent stage by the 40th post-operative day and the accurate prescription of glasses may be given to the patient.
| Summary|| |
With the objective that an aphakic should be able to go back to his job or cease to be a burden to the members of his family for daily routine of life, this study 'was undertaken in 100 recently operated cases of cataract. The study analysed the changes of refraction at varying periods after cataract surgery and an attempt was made to correlate the findings so that an accurate prediction relative to refractive changes may be made. The changes observed were a gradual increase in the spherical refraction (less corneal curvature) and a decrease in the astigmatism (difference between greater and lesser corneal curvatures) till 40th post-operative day. The refractive power of the eye settled down to a permanent stage by the 40th day. The mean value of spherical refraction has been + 11.5 diopters (S.D. ± 1.05) with cylindrical correction of + 0.93 diopter (S.D. ± 0.85) against-the-rule.
| Acknowledgment|| |
We are indebted to Dr. K. N. Shukla, Professor of Ophthalmology, for his valuable guidance. We acknowledge our thanks to Mr. Rangasamy, Statistician, JIPMER Hospital for help in preparing the statistical tables.
| References|| |
BEASLEY, H.: Keratometric changes after cataract surgery. Tr. Amer. Ophth. Soc. 65 : 168 (1967).
DUKE-ELDER, S.: The practice of refraction. The C. V. Mosby Coy. London Ed. 1954, p. 107.
ELENIUS, V. AND KARO, T.: Changes in refractive power of cornea after cataract surgery. E & E.N.T. Monthly 47 : 66, (1968).
FLOYD, G.: Changes of Corneal curvature following cataract extraction. Amer. J. Ophth. 34 : 1525, (1951).
HILDING, A. C.: The experimental approach to cataract surgery. Amer. J. Ophth. 53 : 606, (1962).
KUWAHARA, S.: Changes of Corneal Curvature after cataract surgery and its effects on visual acuity. Acta. Soc. Ophth. (Japan) 37 : 883, (1933).
McLEAN, J. M.: A new corneoscleral suture. Arch. Ophth. 23 : 554, (1940).
MENDOZA, de S.: On suturing o f the cornea (In French) Bull. Soc. Ophth. Paris. 1 : 105 (1888).
NIRANKARI, M. S. and KHANNA, K. K.: Sutures in Cataract Surgery. Orient. A. Ophth. 6 : 8, (1968).
SCHEIE, H. G.: Incision and closure in Cataract extraction. A. M. A. Arch. Ophth. 61 : 431, (1959).
TAYLOR, D. M.: Optimum Wound closure in Cataract Surgery. Amer. J. Ophth. 48 : 660, (1959).
[Figure - 1]
[Table - 1], [Table - 2], [Table - 3], [Table - 4]