myopia and more Flashcards
affect of NS on vision
cause myopic shift even before they cause a decrease in BCVA
cortical cataracts effect on vision
hyperopic shift
elevated glucose levels and vision
cause myopic or hyperopic shift. will be symmetric between the two eyes and most often >1.00D
pseudophakic patients and blood sugar shifts
CANNOT have refractive shift due to elevated blood glucose
inherited myopia
myopia inherited from parents
risks for the development of myopia in kids based on whether their parents have myopia
- no parents with myopia: <10%
- one parent with myopia: 20-25% chance
- both parents with myopia: 30-40% chance
nocturnal myopia
occurs in dimly illuminated surroundings due to minimal visual clues to guide the amount of accommodation that is necessary. this type of myopia particularly causes issues with night driving. Remember that distance vision doe snot require accommodation; however, if there are minimal visual cues to guide accommodation, accommodation will be suspended at an intermediate distance, resulting in a more myopic Rx (the eye will be too powerful)
absolute presbyopia and night myopia
there is no accommodation that could induce night myopia in an absolute presbyope, however could experience it due to an increase in SAs due to dilated pupils in dimly lit condition
pseudo myopia
occurs when an uncorrected hyperbole accommodates to neutralize his RX, but then accommodates too much, resulting in a myopia RX. Dry refraction will show a low amount of myopia, but cyclo refraction will reveal the uncorrected hyperopia. pts with this are often RXed a low plus RX for near only to alleviate symptoms. the low minus RX should NOT be RXed, as it will exacerbate symptoms
things that can cause a myopic shift
NS increased blood glucose scleral buckle diamox NSAIDs topamax
pinhole
increases the depth of focus and depth of field. this increase in depth of focus will improve the patients VA if the reduced VA is due to uncorrected refractive error. in other words, theoretically the patient should have the same VA through the pinhole as at the end of the refraction.
what are pinhole acuities limited by
media opacities an other ocular pathologies
assuming the patient is not wearing his glasses and is an absolute presbyope, at what distance will this patient see most clearly? his Rx is -2.00Ds OU
1/2.00=50cm
the range of clear vision for a patient extends form the near point (the closest point an object can be placed in front of the eye and still be seen as clear when the eye is fully accommodated) and the far point (the farthest point an object can be placed in front of the eye and still seen as clear)
far point
determined by taking the reciprocal of the patients refractive error.
near point
determined by taking the reciprocal of the maximal amount of accommodation the patient can exert. in an absolute presbyope, the near point and the far point will coincide.
far point location
in front of the eye for a myopic patient and behind the eye for a hyperopic patient and infinity for emmetropic patient
which mode of correction is most appropriate to minimize RSM for a high myope with an axial length of 26mm
glasses
what is a normal axial length
24mm
Knapps law
glasses should be rxed for axial ametropes in order to minimize RSM. refractive ametropes are best corrected with CLs which minimize RSM
RSM
is the ratio of the retinal image size in a corrected eye to the retinal image size in a gullstrand emmetropic eye. when RXing, the goat lis to maintain an RSM of appx 1. according to Knapps law, this is achieved in a refractive ametropes when the lens is placed at the entrance pupil of the eye (very near the cornea), and an axial ametrope when the lens is placed at the anterior focal point of the eye (appx 15mm from the cornea)
axial ametropes should be corrected with
glasses
refractive ametropes should be corrected with
CLs
pathological myopia
>6.00D SE or axial length >26.5mm. posterior staphyloma lacquer cracks Fuch's spots obliquely inserted ONHs lattice RDs (both types) CNVMs PPCs premature cataracts glaucoma
angioid streaks
similar to lacquer cracks as they also represent a break in Bruchs membrane that increases the risk of development of a CNVM. recall that angioid streaks are associated with PEPSI (PXE, ED, Paget’s disease, sickle cell anemia, idiopathic)
the COMET study
correction of myopia eval trial
evaluated whether +2.00D PaLs slow the progression of myopia compared to single vision lenses in kids ages 8-12 with 0.75D to 2.50D myopia, a near EP, and an accommodative lag. after 3 years, patients in the PAL progressed 0.87D compared to 1.15D progression in the SV lens group. There was poor compliance in the PAL group. Although this difference in progression between the 2 groups was statistically significant, it is not clinically significant
biggest things to think about with adults and myopic shifts
NS and DM
