There are 10 words that start with 'opto'.
| optometer | optometry |
| optometers | optometric |
| optokinetic | optometries |
| optometrist | optometrists |
| optoelectronic | optoelectronics |
Note: These 10 words that start with 'opto' are found from the USA & Canada version of the tournament Scrabble word list.