Determination of the time of refractive stability after uneventful phacoemulsification in Indian eyes

Abstract

BACKGROUND

Knowledge about refractive stabilization and the accuracy of postoperative refractive error measurements are crucial for improved patient outcomes after phacoemulsification. Existing guidelines typically recommend waiting 4-6 wk before prescribing corrective lenses. Our research focused on identifying factors that influence refractive errors in the early stages of post-cataract surgery, thus contributing to the existing literature on this topic.

AIM

To investigate the time required for refraction stability after uneventful phacoemulsification surgery.

METHODS

We compared the variation and statistical significance of the difference in spherical, cylindrical components, and the spherical equivalent between the 1- and 6-wk follow-up period in a group of 257 eyes that underwent uneventful phacoemulsification with foldable intraocular lens implantation, all performed by a single experienced surgeon. The Wilcoxon-Signed Rank Test was utilized to assess the magnitude of the change and determine its statistical significance. The refractive stability was defined as the point at which the change in spherical equivalent was within ± 0.5 dioptres for two consecutive visits.

RESULTS

The average age of the patients was 64.9 ± 8.9 yr. The differences observed in both the visits in spherical power (0.1 ± 0.2), cylinder power (0.3 ± 0.4), and spherical equivalent (0.2 ± 0.2) were minimal and not statistically significant. The majority of eyes (93.4%) achieved refractive stability within 6 wk after the surgery. The cylindrical power differed between age groups at the 6^th wk post-operative and the difference was statistically significant (P value 0.013). There were no significant differences in refractive stability when considering sex and axial length.

CONCLUSION

Phacoemulsification with foldable intraocular lens implantation results in no significant changes in refraction for the majority of cases during the 6-wk follow-up period. Therefore, a spectacle prescription can be given at the completion of 1 wk.

Key Words: Cataract surgery, Phacoemulsification, Refraction stability, Visual acuity, Spherical equivalent

Core Tip: Achieving refractive stability in Indian eyes after uneventful phacoemulsification involves meticulous preoperative planning, including accurate biometry and corneal assessment, tailored intraocular lens selection, addressing astigmatism, patient education, and diligent postoperative follow-up. These strategies, combined with adapting to new technologies and personalized care, can significantly improve the satisfaction and visual outcomes for patients. Spectacles can be prescribed after 1 wk of completion. This study is the inaugural research focused on Indian eyes, offering an extensive analysis of the factors affecting the time needed to achieve stable vision across different patient groups.

INTRODUCTION

Early visual recovery is a known advantage of Phacoemulsification. Determining the appropriate timing for spectacle prescription after cataract surgery is crucial in providing patients with the best possible visual outcomes and ensuring their post-operative satisfaction. The timeframe for stabilization of refraction varies among individuals and can range from a few weeks to several months[1]. Factors affecting stabilization include the healing process, corneal changes, and adjustments in the eye's focusing power secondary to stability of effective lens position. Research has shown that utilizing smaller incisions during intraocular lens (IOL) insertion leads to accelerated refractive stability and less corneal astigmatism[2-6]. This not only shortens the time required for stabilization but also enhances the clarity of uncorrected vision. Moreover, knowledge about refraction stability and precise post-operative refractive error measurements lead to better outcomes for patients undergoing sequential cataract surgeries, particularly those seeking monovision[7]. Mounting evidence indicates that refractive stabilization happens swiftly after phacoemulsification[1-7]. However, despite this, numerous guidelines continue to recommend waiting for 4-6 wk before prescribing corrective lenses. In light of this, our study aimed to complement the current literature on refractive stabilization and examine various factors that addresses refractive errors in the early stages following routine cataract surgeries.

MATERIALS AND METHODS

Methods

This was a retrospective analysis of 300 case records of patients who underwent surgery by a single surgeon between October 2022 to March 2023. Case records of 254 subjects with 257 eyes which satisfied the inclusion criteria were taken up for the study to analyze the data. Age distribution was divided into three subgroups: < 55 years, 55-65 years, and > 65 years. The axial length (AL) was subdivided into three groups comprising group 1 (< 22 mm), group 2 (22-25 mm), and group 3 (> 25 mm).

Inclusion criteria: All patients who underwent uneventful phacoemulsification underwent uncomplicated phacoemulsification cataract surgery with foldable posterior chamber IOL implantation by the same surgeon, completed both 1^st wk and the 6^th wk follow up and were evaluated by the same optometrist. All patients were evaluated for dry eyes before surgery and those who had Non-invasive tear break up time (NIBUT) ≥ 10 seconds were included.

Exclusion criteria: The study excluded patients who had evidence of dry eye with a NIBUT score less than 10, a prior history of glaucoma, corneal pathology, retinal pathology, traumatic and complicated cataracts that could potentially lead to a poor visual outcome postoperatively. Additionally, patients with comorbid systemic conditions, eventful postoperative periods and non-compliance to follow up were excluded. Preoperative biometry was performed by IOL Master 700 with Barret’s Universal II formula.

Surgical procedure: All surgeries were performed under topical anaesthesia. A clear corneal incision of size 2.2 mm was given on the steep axis and routine steps of phacoemulsification were performed. At the end, hydrophobic, acrylic IOL were placed in the capsular bag. Postoperatively, patients received a topical antibiotics-steroids combination for 2 wk followed by topical non-steroidal anti-inflammatory agents for 4 wk along with lubricants three times daily.

Follow-up: Patients were evaluated after completion of the 1 wk and 6 wk following surgery. Keratometry readings and subjective refraction were performed by a single experienced optometrist. From the refraction measurements, the spherical, cylindrical power and the calculated spherical equivalent [SE = sph + (0.5 × cyl)] were analysed for variation. The axis values were not considered as the meridian position of postoperative astigmatism has a minimal change of effect compared to its magnitude.

Statistical analyses

Descriptive statistics were presented with frequency (percentage) and mean ± SD for the categorical and continuous factor, respectively. Median (interquartile range) was presented for the continuous variable while the data follows non-normal distribution. The normality of the data was assessed by using Shapiro-Wilk test. BCVA by Snellen’s chart was converted to Log MAR. Paired t-test/Wilcoxon Signed Rank test were used to find out the significant difference between time points. Mann Whitney U test was used to find out the significant changes in refraction between males and females. Kruskal -Wallis test was used to find out the significant changes in the refractive error between age group and AL. Box plot graph was performed to visualize the distribution of refractive error for the post-operative time intervals. P value < 0.05 was considered as statistically significant. All the analysis was carried out by using statistical software STATA (14, TX, United States)

RESULTS

The study included a total of 254 subjects (257 eyes) who underwent 2.2 mm phacoemulsification with foldable in-the-bag IOL implantation, all performed by a single experienced surgeon. Three cases were bilateral. Demographic details presented in Table 1 revealed an almost equal male-to-female ratio of 1:1.01, with approximately 49.6% males and 50.4% females. The mean age was 64.9 ± 8.9 years, ranging from 34 years to 90 years. The AL subgroups comprised 55 eyes (21.4%) in group 1, group 2 included 197 eyes (76.6%) and group 3 included 5 eyes (2%). Females were more in number in both group 1 and group 3. The mean IOL power used in the study was 21.6 ± 2.3 dioptres (D) with a range between 12.5-27 D. When the ocular biometric parameters were compared at the two follow ups, it was found that there was no statistically significant difference between the keratometry 1 (K1) and keratometry 2 (K2) readings at both the 1^st wk and 6^th wk postoperatively in all the groups. Out of the 257 operated cases, 240 (93.4%) cases experienced either no change in spherical equivalent or a change within ± 0.5 D. In the remaining 17 (6.6%) cases, changes in cylindrical power were seen in 15 cases, spherical power in 2 cases, and both powers in none of the cases. The mean spherical error value of 0.04 ± 0.4 D (P = 0.851) at the 1-wk follow-up and 0.01 ± 0.3 D at the 6-wk follow-up, with a difference of 0.1 (0.2) between both time points. The mean cylindrical error at the 1-wk follow-up was -0.3 ± 0.7 D, which decreased to -0.2 ± 0.6 D at the 6-wk follow-up, showing a difference of 0.3 (0.40). However, these changes were not statistically significant (P > 0.05). Similarly, the mean refractive spherical equivalent error was -0.05 ± 0.4 D at the 1-wk follow-up and -0.07 ± 0.4 D at the 6-wk follow-up, with a mean difference of 0.2 (0.2) between the two time points as shown in Table 2. No statistically significant differences were found in any of the three groups between the 1^st- and 6^th-wk follow-up values. The refraction stability among the age groups, sex and AL’s at two follow up visits of 1 wk and 6 wk has been tabulated in Tables 3-5 respectively.

Table 1 Demographic details.

Parameters	Axial length, n (%)			Overall	P value1
	Hypermetropia	Emmetropia	Myopia
Age in yr					0.337
< 55	8 (14.5)	21 (10.8)	2 (40)	31 (12.2)
55–65	22 (40)	83 (42.8)	2 (40)	107 (42.1)
> 65	25 (45.5)	90 (46.4)	1 (20)	116 (45.7)
Sex					0.036a
Male	20 (36.4)	105 (54.1)	1 (20)	126 (49.6)
Female	35 (63.6)	89 (45.9)	4 (80)	128 (50.4)
Eye					0.861
Right eye	29 (52.7)	101 (51.3)	2 (40)	132 (51.4)
Left eye	26 (47.3)	96 (48.7)	3 (60)	125 (48.6)
K1-reading (1 wk)1
mean ± SD	43.8 ± 1.7
Range	(39-47.5)
K1-reading (6 wk)1
mean ± SD	43.8 ± 1.7
Range	(39-47.8)
K2-reading (1 wk)1
mean ± SD	44.5 ± 1.7
Range	(39.5-49.5)
K2-reading (6 wk)1
mean ± SD	44.6 ± 1.7
Range	(40-49)

^aP value < 0.05, Chi-square/Fisher’s exact test.

¹Paired t-test/Wilcoxon Sign rank test.

K: Keratometry.

Table 2 Refractive stability at two follow up visits of 1 wk and 6 wk.

Parameters	Post-operative visits			P value1
	1st wk	6th wk	Difference
Sphere				0.851
mean ± SD	0.04 ± 0.4	0.01 ± 0.3	0.1 ± 0.2
Median (IQR)	0 (0-0)	0 (0-0)	0 (0-0)
Range	-1.5 to 1	-0.75 to 1.5	0 to 1.5
Cylinder				0.695
mean ± SD	-0.3 ± 0.7	-0.2 ± 0.6	0.3 ± 0.4
Median (IQR)	-0.5 (-0.75 to 0.5)	-0.5 (-0.75 to 0.5)	0.25 (0 to 0.25)
Range	-3.5 to 1.5	-1.5 to 1.5	0 to 2.75
Spherical equivalent				0.277
mean ± SD	-0.05 ± 0.4	-0.07 ± 0.4	0.2 ± 0.2
Median (IQR)	0 (-0.25 to 0)	0 (-0.25 to 0)	0.12 (0 to 0.25)
Range	-1.75 to 1.37	-1 to 1.75	0 to 1.5

¹Wilcoxon Sign rank test to compare refractive error between 1^st wk and 6^th wk post-operative.

IQR: Interquartile range.

Table 3 Refractive stability by age distribution.

Parameters	1-wk post-operative			6-wk post-operative			P value1	P value2	P value3
	Age in yr			Age in yr
	< 55	55-65	> 65	< 55	55-65	> 65
Sphere							0.392	0.451	> 0.99
mean ± SD	-0.05 ± 0.4	0.1 ± 0.4	0.01 ± 0.4	-0.12 ± 0.3	0.03 ± 0.4	0.04 ± 0.3
Median (IQR)	0 (0-0)	0 (0-0)	0 (0-0)	0 (-0.5 to 0)	0 (0-0)	0 (0-0)
Range	-0.75 to 1	-0.8 to 1	-1.5 to 1	-0.75 to 0.75	-0.75 to 1.5	-0.5 to 1
Cylinder							0.769	0.408	0.717
mean ± SD	-0.6 ± 0.1	-0.2 ± 0.7	-0.3 ± 0.7	-0.5 ± 0.3	-0.1 ± 0.6	-0.4 ± 0.7
Median (IQR)	-0.5 (-0.75 to -0.5)	-0.5 (-0.5 to 0.5)	-0.5 (-0.75 to 0.5)	-0.5 (-0.5 to 0.5)	-0.5 (-0.5 to 0.5)	-0.5 (-0.75 to 0.5)
Range	-0.75 to 0.5	-3.5 to 1	-1.5 to 1.5	-1 to 0.5	-0.75 to 1.25	-1.5 to 1.5
Spherical equivalent							0.173	0.894	0.249
mean ± SD	-0.1 ± 0.4	-0.01 ± 0.4	-0.1 ± 0.4	-0.2 ± 0.3	-0.01 ± 0.4	-0.1 ± 0.3
Median (IQR)	0 (-0.37 to 0)	0 (-0.25 –0.25)	0 (-0.25 –0)	0 (-0.31– 0)	0 (-0.25 –0.25)	0 (-0.25 –0)
Range	-0.87 to 1	-1.75 to 1	-1.5 to 1.37	-1 to 0.5	-1 to 1.75	-1 to 0.87
P value4	0.358			0.287			-
P value5	0.052			0.013
P value6	0.246			0.057

¹Wilcoxon Sign rank test to compare the patients with age < 55 yr between 1^st wk and 6^th wk post-operative.

²Wilcoxon Sign rank test to compare the patients with age 55 yr to 65 yr between 1^st wk and 6^th wk post-operative.

³Wilcoxon Sign rank test to compare the patients with age > 65 yr between 1^st wk and 6^th wk post-operative. Boldface indicates statistical significance.

⁴Kruskal-Wallis test for comparing age and spherical power.

⁵Kruskal-Wallis test for comparing age and cylindrical power.

⁶Kruskal-Wallis test for comparing age and spherical equivalent.

IQR: Interquartile range.

Table 4 Refractive stability by sex wise distribution.

Parameters	1 wk postoperative			6 wk postoperative			P value1	P value2
	Male	Female	P value3	Male	Female	P value3
Sphere			0.523			0.281	0.698	0.933
mean ± SD	0.06 ± 0.4	0.03 ± 0.4		0.05 ± 0.4	-0.03 ± 0.3
Median (IQR)	0 (0-0)	0 (0-0)		0 (0-0)	0 (0-0)
Range	-1.5 to 1	-0.75 to 1		-0.5 to 1.5	-0.75 to 1
Cylinder			0.979			0.585	0.788	0.783
mean ± SD	-0.3 ± 0.6	-0.3 ± 0.7		-0.3 ± 0.6	-0.2 ± 0.6
Median (IQR)	-0.5 (-0.8 to 0.5)	-0.5 (-0.8 to 0.5)		-0.5 (-1.5 to 1)	-0.5 (-0.5 to 0.5)
Range	-1.5 to 1.25	-3.5 to 1.5		-1.5 to 1	-1 to 1.5
Spherical equivalent			0.651			0.724	0.419	0.464
mean ± SD	-0.04 ± 0.4	-0.1 ± 0.4		-0.1 ± 0.4	-0.1 ± 0.4
Median (IQR)	0 (-0.25 to 0)	0 (-0.25 to 0)		0 (-0.25 to 0)	0 (-0.25 to 0)
Range	-1.5 to 1.12	-1.75 to 1.37		-0.87 to 1.75	-1 to 1

¹Wilcoxon Sign rank test to compare the male between 1^st wk and 6^th wk post-operative.

²Wilcoxon Sign rank test to compare the female between 1^st wk and 6^th wk post-operative.

³Mann Whitney U test.

IQR: Interquartile range.

Table 5 Refractive stability by axial length wise distribution.

Parameters	1 wk post operative			6 wk postoperative			P value1	P value2	P value3
	Axial length in mm			Axial length in mm
	< 22	22-25	> 25	< 22	22-25	> 25
Sphere							> 0.99	0.989	0.317
mean ± SD	0.1 ± 0.4	0.1 ± 0.4	-0.2 ± 0.4	0.04 ± 0.3	0.01 ± 0.3	-0.2 ± 0.3
Median (IQR)	0 (0-0)	0 (0-0)	0 (-0.75 to 0)	0 (0-0)	0 (0-0)	0 (-0.5 to 0)
Range	-0.75 to 1	-1.5 to 1	-0.75 to 0	-0.75 to 1	-0.75 to 1.5	-0.5 to 0
Cylinder							0.765	0.783	0.782
mean ± SD	-0.1 ± 0.7	-0.3 ± 0.6	-1.6 ± 1.7	-0.2 ± 0.6	-0.2 ± 0.7	-0.8 ± 0.4
Median (IQR)	-0.5 (-0.6 to 0.5)	-0.5 (-0.75 to 0.1)	-0.75 (-3.5 to -0.5)	-0.5 (-0.5 to 0.5)	-0.5 (-0.75 to 0.5)	-0.75 (-1.2 to -0.5)
Range	-1.5 to 1.25	-1.5 to 1.5	-3.5 to 0.5	-1.25 to 0.75	-1.5 to 1. 5	-1.25 to 1.5
Spherical equivalent							0.982	0.19	0.477
mean ± SD	-0.01 ± 0.4	-0.1 ± 0.4	-0.6 ± 0.7	-0.04 ± 0.3	-0.1 ± 0.4	-0.4 ± 0.3
Median (IQR)	0 (-0.25 to 0.25)	0 (-0.25 to 0)	-0.37 (-1 to 0)	0 (-0.25 to 0.25)	0 (-0.25 to 0)	-0.37 (-0.62 to 0)
Range	-1 to 1	-1.5 to 1.37	-1.75 to 0	-1 to 1	-1 to 1.75	-0.75 to 0
P value4	0.559			0.657			-
P value5	0.123			0.226
P value6	0.091			0.164

¹Wilcoxon Sign rank test to compare the patients with axial length < 22 mm between 1^st wk and 6^th wk post-operative.

²Wilcoxon Sign rank test to compare the patients with axial length 22 to 25 mm between 1^st wk and 6^th wk post-operative.

³Wilcoxon Sign rank test to compare the patients with axial length > 25 mm between 1^st wk and 6^th wk post-operative.

⁴Kruskal-Wallis test for comparing axial length and spherical power.

⁵Kruskal-Wallis test for comparing axial length and cylindrical power.

⁶Kruskal-Wallis test for comparing axial length and spherical equivalent.

IQR: Interquartile range.

DISCUSSION

Phacoemulsification techniques and foldable IOLs have become the prevailing standard of care in today’s eye care setting. These modern approaches have led to smaller incision sizes, resulting in reduced induced astigmatism, which do stabilize more quickly resulting in early visual recovery. As cataract surgery has become more common among younger individuals, who are still in their pre-retirement years, and considering the growing reliance on near vision in the digital era, it becomes essential to optimize vision as soon as possible for the patients’ benefit. The objective of this research was to gain a deeper understanding of the existing guidelines for spectacle prescription after cataract surgery, with the ultimate goal of enhancing the quality of life for patients during the post-operative phase.

Numerous publications have focused on determining the period required for refraction stabilization after phacoemulsification, aiming to find the most optimal time for prescribing corrective glasses to patients[8,9]. One such investigation was carried out by Berk et al[9], who studied 1838 eyes that underwent phacoemulsification manually and with a femtosecond laser[10]. Both methods indicated that visual acuity and refraction stabilized 3 wk after the procedure. In a separate study by Sugar et al[10], refraction stabilization (spherical equivalent, cylinder, and cylinder axis) was achieved within 1 wk[4]. This result was also supported by de Juan et al[4], who found that refraction stabilized after 1 wk of phacoemulsification surgery[4]. The present study also supports the fact that the refractive stability is achieved at the end of 1 wk of an uneventful phacoemulsification in Indian eyes.

The present study shows that refractive stability is independent of the demographic parameters such as age and sex similar to the study by Mrugacz et al[11] where the findings were not statistically significant[11]. Comparing the AL as a variable, it was found that the stabilization of refraction in the 3^rd wk was achieved in 91% of the emmetropic, 77% of the myopic, and 46% of the hypermetropic patients, respectively. Similarly in the present study, 175/197 (88.8%) of patients in group 2 (AL = 22-25 mm), 48/55 (77.3%) in patients in group 1 (AL ≤ 22 mm) and 3/5 (60%) of patients in group 3 (AL ≥ 25 mm) experienced refractive stability within 0.5 D at the end 1 wk after the procedure. The maximum observed difference in spherical equivalent between the 1^st wk and the 6 wk was 1.5 D. Stabilization of refraction at completion of 6 wk was achieved in a little higher percentage in group 2 eyes (89.8%), constant in group 3 eyes but a significantly higher percentage in 92.7% group 1 eyes.

There was no statistically significant difference observed in the mean keratometry corneal astigmatism between 1^st wk and 6^th wk after the surgery. The average astigmatism at 1 wk postoperatively was 0.3 ± 0.7 D, and at 6 wk postoperatively was 0.2 ± 0.6 D. Similarly, the 1^st wk K1 value was 43.8 ± 1.7 D, and at 6 wk there was no change in the values, whereas 1^st wk mean K2 value was 44.5 ± 1.7 D (39.5-49.5) and at 6 wk postoperatively, it was 44.6 ± 1.7 D (40–49). However, there were no statistically significant differences among all these values (P > 0.05 for all variables, Paired t test/Wilcoxon Sign rank). It suggests that refractive stability is independent of the corneal keratometry values throughout the observational period which has not been studied in any of the published literature.

A study by Landers et al[12] tried to find out whether any refractive shift occurs with different varieties of IOL, however they could not find any statistically significant difference when IOL with rigid haptics or with pliable haptics were used[12]. In the present study however, only one type of foldable IOLs with pliable haptics were used and therefore there was no chance of bias due to variable lens models with different types of haptics, which may impact the lens stabilization period.

In the present study, out of 17 eyes which had a significant refractive change only 2 eyes had change in sphere more than 0.5 D which can be due to anterior or posterior displacement of the IOL bag complex due to capsular contraction. The rest of the 15 eyes out of 257 eyes which is about 6% eyes had a change in astigmatism more than 0.5 D between their 1-wk and 6-wk values. The possible reasons may be increase in phaco energy used for emulsification which could have modulated the wound more to cause a delayed change in corneal astigmatism or wound stretch caused by insertion of thicker IOL or IOL with high dioptric value. Since we have not analysed the refraction stability considering these variables, it is not possible to conclude the reason for the delayed change of astigmatism.

The strength of our study is that a single experienced optometrist performed the subjective manifest refraction at both the postoperative visits, the 1^st wk and end of 6 wk which gives more precise results than an auto refractometer as is also supported by Kozlov et al[13]. Secondly, an optical biometer was used to perform the ocular biometric measurements which can perform better than an ultrasound biometer. The high postoperative emmetropic accuracy in our study was also due to the use of Barret’s universal II IOL power calculator and using the steep axis for incision.

The limitation of the study is the retrospective nature of the study due to which a better standardization could not be done. Moreover, there were no control points between the 1^st wk and 6 wk after surgery. Even though the shorter and longer eyes took longer than the normal length eyes for refraction stability, it was not statistically significant. One limitation of our study is that if we give early spectacle dispensing, the subjective satisfaction of patients after 6-8 wk of spectacle dispensing needs to have been studied. A change in spherical or cylindrical value of more than 0.5 D will surely affect the subjective acceptance of the patients and with increase in digital platform use, the eye strain would be much more. So, in 6.6% of our patients, an early dispensing of spectacle would have led to a refractive instability and would have made a necessity to change their spectacle power after the last follow up.

Therefore, a prospective cohort study including a greater number of short and long eyes, subjective satisfaction questionnaire outcomes and a long term follow up may be needed in future to evaluate the AL dependency and the time frame for refractive stability.

CONCLUSION

Refraction after cataract surgery stabilizes at the end of the 1^st wk in a majority of cases, especially in eyes in between 22 to 25 mm AL and therefore is a safe time for prescribing corrective glasses to all these patients irrespective of age and sex.