The reason why your eye prescription is so expensive is because they have high retail markups as well as the cost of specialized materials needed to make the prescription lenses and the manufacturing process as well as the limited competition.
Retailers of prescription eyeglasses and contact lenses often mark up the cost of the frames and lenses which contribute to the overall price and they know they can get away with it because people need the glasses and contact lenses.
The eyeglasses and eyewear industry is also dominated by a few major players, which too can lead to the higher prices and less price competition.
Also a single company, called EssilorLuxottica, controls a large portion of the eyewear market, and owns many well known brands and retail chains.
Eyeglasses are also made from various specialized materials, including durable and lightweight options such as titanium as well as acetate for frames and lenses with specialized coatings for scratch resistance, anti glare and UV protection.
Also creating or making prescription lenses for eyeglasses requires a high level of precision and customization, especially for complex prescriptions like progressive lenses which also adds to the cost of the eye prescription or eyeglasses.