An apparatus for photothermal ophthalmic treatment, in particular photocoagulation or photo-thermal stimulation, the apparatus comprising a diagnostic instrument and an adapter unit, the diagnostic instrument being configured to emit illumination light from an illumination output along a free- air illumination output path towards a target area, to receive light from the target area along a free-air viewing path and to provide a magnified view of the target area, wherein the adapter unit comprises: a housing detachably mountable to said diagnostic instrument； at least one treatment direct diode laser positioned within the housing； the direct diode laser comprising a treatment laser diode configured to emit light at a wavelength suitable for photothermal ophthalmic treatment in the wavelength range of 480 and 632 nm, one or more optical elements configured to direct the emitted light as a treatment light beam towards the target area when the housing is mounted to said diagnostic instrument； and wherein the treatment direct diode laser is located above or in line with said viewing path when the housing is mounted to said diagnostic instrument and wherein at least one of the optical elements is configured to extend into at least one of the free-air viewing path and the free-air illumination output path of the diagnostic instrument when the housing is mounted to said diagnostic instrument in an operational position.L'invention concerne un appareil de traitement ophtalmique photothermique, en particulier de photocoagulation ou de stimulation photothermique, l'appareil comprenant un instrument de diagnostic et une unité adaptateur, l'instrument de diagnostic étant conçu pour émettre une lumière d'éclairage à partir d'une sortie d'éclairage le long d'un trajet de sortie d'éclairage à air libre vers une zone cible, pour recevoir de la lumière provenant de la zone cible le long d'un trajet de visualisation à air libre et pour fournir une vue agrandie de la zone cible, l'unité
