Is it permissible to sell analysis devices that were purchased with dedicated donations for that purpose, but have not been used due to the unavailability of doctors, and to buy ophthalmology devices with the proceeds, knowing that the donors specifically donated for the purchase of analysis devices?

The basic principle is that money collected for a specific purpose should only be spent on that purpose. If the benefit of the analysis devices purchased with the donated money becomes defunct, it is permissible to sell them and purchase other devices that people need. There is no need to refer back to the donors to save the devices from damage and use the money for what is closer to their original intention. However, if it was realized that the benefit of the devices would become defunct before their purchase, then it would be necessary to seek the donors' permission for the new purpose.