I suffered from an extremely rare form of blindness. Although I still had my sight, what I saw was completely different from what everyone else could see. I did all I could to disguise my disability by listening very carefully to what was going on around me.

On the morning of my fiftieth birthday my sisters-in-law led me outside to see my presents. I knew from memory that I was staring out onto a suburban street in the East Midlands. However all I could see was a beautiful sunset over the hills of South Harris.

I heard the engine of a high performance car, and concluded that TPR and my brother-in-law R were test-driving one of my birthday surprises. It sounded like a sleek black Porsche 911.

From further in the distance I could hear a blast of pop music and the excited shrieks of my nephew and nieces. I guessed that they were playing some kind of dance pad game in a neighbour’s garden.

I chatted excitedly to the others about what I could “see”. So far so good – but for how much longer could I keep up my pretence of vision?