For example, a 1000 Hz tone in an unaffected ear may be heard as a slightly different pitch in the opposite ear, or have an imperfect tonal quality in the affected ear. Biological explanation via theories of pitch of pure tones
There are two theories on the cause of diplacusis: place theory and temporal theory. Place theory posits that  the cause is looking for the edge of the wave for the pitch and could explain diplacusis as a small differences between the two cochleas.Temporal theory posits that the cause is from looking at the phase locking to tell what the pitch is. This theory has a difficult time explaining diplacusis. There are some examples of pitch which do not have an "edge" on the basilar membrane, which this would account for—e.g., white noise, clicks, etc. Both theories are under debate. Effects of sensorineural hearing loss
Normal human ears can discriminate between two frequencies that differ by as little as 0.2%. If one ear has normal thresholds while the other has sensorineural hearing loss (SNHL),  diplacusis may be present, as much as 15–20% (for example 200 Hz one ear => 240 Hz in the other). The pitch may be difficult to match because the SNHL ear hears the sound "fuzzy". Bilateral SNHL gives less diplacusis, but pitch distortions may persist. This may cause problems with music and speech understanding. Treatment
Treatment of diplacusis includes a full medical and audiological examination that may explain the nature of the problem. If needed, amplification may relieve the symptoms of diplacusis.
A Brazilian study published in 2005 found that 34% of the students in one city were astigmatic. Regarding the prevalence in adults, a recent study in Bangladesh found that nearly 1 in 3 (32.4%) of those over the age of 30 had astigmatism.A Polish study published in 2005 revealed "with-the-rule astigmatism" may lead to the onset of myopia.A number of studies have found the prevalence of astigmatism increases with age. History
As a student, Thomas Young discovered that he had problems with one eye in 1793. In the following years he did research on his vision problems. He presented his findings in a Bakerian Lecture in 1801.Independent from Young, George Biddell Airy discovered the phenomenon of astigmatism on his own eye. Airy presented his observations on his own eye in February 1825 at the Cambridge Philosophical Society. Airy produced lenses to correct his vision problems by 1825, while other sources put this into 1827 when Airy obtained cylindrical lenses from an optician from Ipswich. The name for the condition was given by William Whewell.By the 1860s astigmatism was a well established concept in ophthalmology, and chapters in books described the discovery of astigmatism.In 1849, Irish English physicist and mathematician George Stokes invented Stokes lens to detect astigmatism. In 1887 American ophthalmologist Edward Jackson revised the Stokes lens concept and made a cross cylinder lens to refine power and axis of astigmatism. In 1907 Jackson described determination of the axis of a correcting cylinder in astigmatism using a cross cylinder.