Does EVLT work to prevent future spider veins?

Spider veins and varicose veins are often associated with reflux or backwards flow in larger veins that transmit pressure to the smaller veins causing them to enlarge.  An ultrasound evaluation can determine which of these veins are affected. Treatment with EVLT of these larger veins eliminates the source of pressure and makes it less likely to develop complex spider and/or varicose veins in the future.  The smaller veins that are already there should be treated with sclerotherapy after EVLT for the best results.

Hi RQ.  Theoretically yes.  EVLT should improve the overall cardiovascular health of the legs which in turn should help prevent future spider veins.  With that said, the condition that causes spider veins and varicose veins is not being "cured".  Rather you are getting better and trying to maintain your current situation.  You will see deterioration of the vascular system again as you age and this can lead to more varicose or spider veins.If the vessels are small (spider veins) you have options like sclerotherapy and (external) laser treatments.  Good luck.

If there is a vein with venous insufficiency and reflux feeding an area of spider veins, then yes, EVLT is a component of treatment. 
I have, however, heard of physicians telling patients to treat these veins as prophylaxis, even if they are normal, in order to prevent spider veins. This is not good advice. Closing normal veins may stimulate the formation or appearance of additional spider veins.

Yes, it does. EVLT fixes the underlying, deep-root cause of your spider veins. Spider veins arise from high pressure in connecting, underlying deeper veins that you can only see with ultrasounds. Therefore, fixing the deeper causes first fixes the prevalent spider veins and stops more from occurring. 

If EVLT is being considered will not specifically be to treat spider veins that you might already present or for future prevention purposes. However, Endovenous laser therapy (EVLT) could be used to treat an underlying venous insufficiency problem in one or more of the superficial veins actively presenting reflux. Almost alway an ultrasound evaluation of your legs is part of your initial evaluation by your vein specialist. This diagnostic test will help determine if an underlying venous insufficiency is causing more superficial changes in the form of spider veins that are very close to your skin. Other signs and symptoms are varicose veins, leg or ankle swelling, leg heaviness and fatigue, leg pain, aching or cramping, burning or itching of the skin, restless legs, skin changes or rashes, ulcers, open wounds, or sores. Many factors contribute to the presence of venous reflux including age, gender, family history, heavy lifting, multiple pregnancies, obesity, and prolonged standing. Healthy leg veins contain valves that open and close to help the blood return back to the heart. Venous reflux disease develops when the valves that keep blood flowing out of the legs and back to the heart no longer function, causing to pool in the legs and leading to signs and symptoms already mentioned. Your physician can help you make informed health care decision on the best treatment for you according to the ultrasound results if they are positive for reflux. On the other hand if reflux is not present and you want to treat spider veins cosmetically there are options that you can also discuss with your physician about. If venous reflux is not present in the diagnostic test and signs and symptoms are not significant, EVLT or any other thermal energy more traditional treatment or any other closure system to treat the main superficial veins are not recommended. Consider other treatments like sclerotherapy or laser sclerotherapy to treat spider veins. 
All the best,