▁ 3 3 0 ▁ms , ▁although ▁there ▁is ▁a ▁large ▁vari ability ▁in ▁this ▁approximation . ▁This ▁vari ability ▁is ▁mostly ▁due ▁to ▁the ▁properties ▁of ▁an ▁image ▁and ▁in ▁the ▁task ▁being ▁carried ▁out , ▁which ▁impact ▁both ▁bottom - up ▁and ▁top - down ▁processing . ▁The ▁mask ing ▁of ▁an ▁image ▁and ▁other ▁de grad ations , ▁such ▁as ▁a ▁decrease ▁in ▁l umin ance , ▁during ▁fix ations ▁( fact ors ▁which ▁affect ▁bottom - up ▁processing ), ▁have ▁been ▁found ▁to ▁increase ▁the ▁length ▁of ▁fix ation ▁dur ations . ▁However , ▁an ▁enh ancement ▁of ▁the ▁image ▁with ▁these ▁factors ▁also ▁increases ▁fix ation ▁dur ations . ▁Fact ors ▁which ▁affect ▁top - down ▁processing ▁( e . g . ▁bl urr ing ) ▁have ▁been ▁found ▁to ▁both ▁increase ▁and ▁decrease ▁fix ation ▁dur ations . ▁ ▁Dis orders ▁ ▁Sym pt oms ▁▁ ▁Pat ients ▁with ▁eye ▁movement ▁dis orders ▁may ▁report ▁dip lop ia , ▁n yst ag mus , ▁poor ▁visual ▁ac u ity ▁or ▁cos met ic ▁b lem ish ▁from ▁squ int ▁of ▁the ▁eyes . ▁ ▁C ause ▁▁ ▁Inner v ational ▁ ▁Su pr an uc lear ▁ ▁N uc lear ▁ ▁N erve ▁ ▁Syn ap se ▁ ▁Mus cle ▁anom al ies ▁ ▁Mal development ▁( e . g . ▁Hy pert ro phy , ▁at ro phy / d yst ro phy ) ▁ ▁Mal insert ion ▁ ▁Sc arring ▁secondary ▁to ▁alignment ▁surg ery