Is it possible to replace eyelashes that you have lost for a unknown reason? I have a visible space in my left eyelashes (Photo)

I suggest PRP and steroid injections if this was lost rapidly.  Latisse everyday should help if this is not an alopecia from autoimmune conditions.  Best, Dr. Emer.

Latisse or Revitalash will only work if the follicles are still alive. If the follicles are "dead and gone" from accidents/trauma, surgery, scars, styes, or eyelash extension damage, you may be a candidate for eyelash transplants. What is an eyelash transplant? The eyelash implant procedure provides a comfortable, permanent restoration of living and growing hair follicles to the eyelid where the eyelash gap exists. Eyelash transplantation is a common procedure I have performed at Bauman Medical for over 15 yrs and my proven techniques are detailed in the top textbooks on Hair Transplantation.  Eyelash implants take several hours to perform, but there is little activity restriction during the cosmetic healing phase which takes about a week.
The main "downside" is that you will have to trim the eyelashes, grooming them to the desired length because the implanted follicles come from the back of the scalp. 

If the hair follicle hasn't been badly damaged, latisse could help the hair to grow back. It's certainly worth a try. You will need to use it regularly for 3-4 months to see. If, at that point, you don't have results, you could look into a hair transplant or if you could always just have individual false lashes applied to the area. However, they will need to be replaced every time they fall off. Hope this helps, Dr. Nazarian