Digital simulation is crucial for improving production systems in Industry 4.0 manufacturing. This research focuses on developing a discrete-event simulation model to enhance capacity and resource planning in the Surface Treatment section of making Intraocular Lenses (IOLs) to prepare for high demand. A production system simulation model was developed using FlexSim software. It simulates the production flows of Monofocal and Hybrid IOLs through both automated and manual stages. The developed model can identify the bottlenecks, suggest capacity adjustments, and support resource allocation experimentation. Various scenarios were explored to examine the effects of increased daily batch loads and machine capacity of the main bottleneck through utilization analysis. The statistical analysis showed significant performance improvements when increasing bottleneck machine capacity from 9 to 11 units during high demand. It led to a remarkable 9.95% rise in average daily throughput, which is from 12.771 to 14.042 batches. Also, the bottleneck machine's utilization dropped from 88.94% to 72.83%. This research highlights how simulation serves as an effective decision-making tool for capacity planning. It helps organizations optimize resource use, reduce potential economic losses, adapt to changing demands, and promote sustainable practices in line with Industry 4.0 principles in manufacturing.