Binocular Vision Anomalies After Cataract and Refractive Surgery

There are indications in the literature that binocular vision disorders may occur after cataract and corneal refractive surgery. It is not clear whether these problems are new or represent decompensation of previously existing conditions. However, the following significant study limitations exist in the current literature: 1) lack of attention to non-strabismic binocular vision disorders, 2) incomplete binocular vision assessment, 3) a validated symptom survey was not used, 4) diplopia was typically the only symptom studied, 5) retrospective study design, and 6) in the few prospective studies the sample sizes were small.

Given the limitations in the current literature there is a need for further study of the prevalence and significance of binocular vision problems after cataract surgery and binocular vision and accommodative problems after corneal refractive surgery.

This study aims to determine whether there is an increase in the prevalence of binocular vision problems after cataract surgery and accommodative and binocular vision disorders after refractive surgery.

1. Research plan Specific aim 1A: To investigate the prevalence of non-strabismic and strabismic binocular vision anomalies after cataract surgery. Specific aim 1B: To investigate the prevalence accommodative and binocular vision disorders after refractive surgery. Specific aim 2: To determine if increase in the prevalence of binocular anomalies is different for cataract surgery compared to refractive surgery. Specific aim 3: To develop an efficient examination protocol that would enable eye care professionals to determine if a patient is at risk for binocular vision anomalies after cataract surgery and accommodative and binocular vision disorders after refractive surgery.

   The proposed study will address the weaknesses in the current literature. The study will be prospective and will use explicit and well-defined eligibility and exclusion criteria. A comprehensive battery of accommodative (pre-presbyopes only) and binocular vision tests will be administered on all the patients before the surgery of the first eye and 12 weeks after the surgery of the second eye.

   A pre-defined classification protocol will be used to determine if a binocular vision disorder is present before surgery, after surgery, or whether there has been a change in the condition after surgery.

   A total prevalence of postoperative strabismic and non-strabismic binocular vision anomalies will be determined for the cataract population and the refractive error group.
2. Statistical analysis plan 2.1 Specific aim 1A Hypothesis: There will be a statistically significant increase in the prevalence of binocular vision anomalies after cataract surgery

A sample size calculation based on a McNemar's test to compare the prevalence of binocular vision anomalies before and after cataract surgery was performed using the Power and Sample Size Program (PS version 3.1.2). Base on a previous literature, the overall prevalence of accommodative and binocular vision anomalies in adult population (18-35 years) is 13.15%. However, no existing literature reported the prevalence of binocular vision anomalies after cataract surgery.

We propose that 15% increase in prevalence is clinically meaningful. The correlation between paired observations is 0.2, as recommended by Dupont. Although this is a large effect, the effect of cataract surgery on prevalence of binocular vision anomalies may be this large (presumed by an experienced binocular vision specialist). If the effect is smaller and the difference not statistically significant, the study will provide valuable data to plan another study. Therefore, a sample size calculation suggests that a total of 44 participants will yield a power of 80% with a significant level of 5%. To account for potential loss to follow-up, a sample size of 50 will be selected for the cataract group. All analyses will be performed using SPSS Statistics 24.0 with an alpha level of 0.05 to determine the statistical significance. A calculation for the prevalence of binocular vision anomalies before and after surgery will be performed. A two-tailed McNemar's Chi-Square Test will be used to test the statistical significance of the change in the proportion of binocular vision anomalies before and after surgery.

2.2 Specific aim 1B Hypothesis: There will be a statistically significant increase in the prevalence of binocular vision and accommodative anomalies after refractive surgery.

The sample size calculation process for specific aim 1B was the same as for specific aim 1A. Therefore, a sample size of 50 will also be selected for the refractive error group. A calculation for the prevalence of accommodative and binocular vision anomalies before and after surgery will be performed. A two-tailed McNemar's Chi-Square Test will be used to test the statistical significance of the changes in the proportions of binocular vision anomalies before and after surgery.

2.3 Specific aim 2 Hypothesis: The increase in prevalence of binocular vision anomalies will be greater after cataract surgery than refractive surgery.

A calculation for the prevalence of binocular vision anomalies will be performed respectively in the cataract group and the refractive error group. A two-tailed Contingency Chi-Square Test will be used to test the statistical significance of difference of changes in the proportion of binocular vision anomalies before and after surgery in both groups.

2.4 Specific aim 3 Hypothesis: A short screening protocol will be of equal effectiveness to a comprehensive assessment of binocular vision and accommodation to determine which patients may be at risk for post-surgical binocular vision and accommodative anomalies.

A two-tailed MacNemar's Chi-Square Test will be used to test the statistical significance of difference in the effectiveness of a short screening protocol and a comprehensive assessment for determining the risk for post-surgical binocular vision and accommodative anomalies. Sensitivity and specificity for the short screening protocol will be calculated.

Eligibility Criteria:
Inclusion Criteria:

* Cataract patients who are willing to undergo cataract extraction and intraocular lens implantation
* Refractive error patients who are willing to undergo laser corneal refractive surgery
* 18 years and older in cataract group
* 18-35 years old in refractive error group
* Any gender
* Any race or ethnicity
* Informed consent and willingness to participate in the study

Exclusion Criteria:

* Other ocular pathology that affect vision and binocular alignment in addition to cataract or refractive error
* Surgical complications that may affect binocular vision testing, such as a subluxation of the IOLs or macular edema