FREE NBEO Applied Basic Science Questions and Answers
A +7.00 D lens has a real object located 20 cm from the lens. The conjugate image is:
Explanation:
With a +7.00 D lens and a real object 20 cm from the lens, the image is real and located 50 cm from the lens. This is because the lens equation yields this result.
The near point of accommodation (NPA) of a patient wearing a +1.25 D Add over his best distance correction is 19 cm. If the Add is removed, the NPA would then be at approximately:
Explanation:
The near point of accommodation (NPA) is the closest point to the eyes at which clear vision is maintained through accommodation. When a patient wears a reading addition (Add), the NPA is brought closer. Removing the Add will push the NPA farther away. Since the patient's NPA with the Add is 19 cm, removing the Add would approximate the NPA to be at a greater distance, around 25 cm.
An eye under the influence of an extremely strong miotic agent has a pupil diameter of 1 mm. The resolution of this eye is considered to be limited by:
Explanation:
When the pupil diameter is very small (like 1 mm under the influence of an extremely strong miotic agent), the resolution of the eye is mainly limited by diffraction. Diffraction causes light waves to bend around the edges of the pupil, leading to a blurring effect on the image formed on the retina.
A 21-year-old patient has a history of previously uncorrected simply hyperopic astigmatism of 3.00 D in each eye. Which of the following is MOST likely to be associated with the patient's refractive error?
Explanation:
Simply hyperopic astigmatism, especially if uncorrected during childhood, can lead to meridional amblyopia in both eyes. This occurs when the brain suppresses or ignores the blurred images from one or both eyes, resulting in reduced visual acuity.
As an emmetropic patient fixates an object at 33 cm, you find retinoscopic neutrality at a distance of 67 cm. You should conclude that the accommodative response:
Explanation:
Retinoscopic neutrality occurring at a distance farther than the point of fixation indicates that accommodation is not fully relaxed. In this case, since the retinoscopic neutrality is found at 67 cm while fixating at 33 cm, there's a lag of accommodation. The difference in reciprocal distances (1/67 - 1/33) gives the amount of lag, which is approximately 1.50 D. Therefore, the accommodative response lags behind the accommodative stimulus by 1.50 D.
The Jackson crossed cylinder subjective test begins with a -1.00 -1.75 x 090 lens in front of a patient's eye. If the correcting cylinder power is changed to -0.75 x 090, then the spherical power should now be:
Explanation:
In the Jackson crossed cylinder subjective test, when the correcting cylinder power is changed from -1.00 -1.75 x 090 to -0.75 x 090, the spherical power should be adjusted in the opposite direction. Since the cylinder power is being reduced by 0.25 D (from -1.75 to -1.00), the spherical power should be increased by the same amount to maintain the patient's prescription. Therefore, the new spherical power should be -1.50 DS.
A 53-year-old male complains of occasional blur at a distance and near. His visual acuities are 20/30 in each eye at distance and near with his present lens correction of +1.00 DS OU, Add +1.75 D. Your distance refraction for 20/20+ acuity is +1.50 DS OU. The BEST tentative Add for the new prescription will have the power of:
Explanation:
To find the added power, subtract the distance refraction (+1.50 DS OU) from the near refraction (+1.00 DS OU + Add). This gives us +1.75 D. Therefore, the best tentative add for the new prescription is +1.75 D.
A lens is made of glass with a refractive index of 1.65. What would be the refractive index for the ideal anti-reflection coating?
Explanation:
An ideal anti-reflection coating aims to minimize reflection by having a refractive index that's the geometric mean of the lens material (1.65) and air (approximately 1.0). So, the coating's refractive index would be approximately 1.28.
A patient's corneal topography map shows steepening of the vertical meridian in a "bow-tie" pattern. This indicates that the patient has:
Explanation:
A "bow tie" pattern on a corneal topography map indicates with-the-rule astigmatism, where the steepest meridian is vertical (aligned with the rule of the topography map).
In diabetic patients, a relative increase in which of the following refractive conditions is MOST associated with an increase in serum glucose levels?
Explanation:
An increase in serum glucose levels in diabetic patients is most associated with a relative increase in myopia. This is because fluctuations in blood sugar levels can cause changes in the refractive state of the eye, leading to temporary increases in myopia.
A head tilt toward the left shoulder is MOST likely due to a paresis of the right:
Explanation:
A head tilt toward the left shoulder is most likely due to a paresis of the right superior oblique muscle. This muscle normally acts to depress the eye when it is adducted (turned inward), so weakness or paresis of this muscle can result in an inability to properly depress the eye when looking inward, leading to a compensatory head tilt.