Scleral Contact Lenses. Scleral contact lenses are a specialized type of contact lens used for managing a variety of eye conditions. They are large, and typically their diameter is 16-20mm. This is twice the size of a standard gas permeable contact lens and larger than a typical soft contact lens. Scleral contact lenses are custom made for each eye.
The loudness of sound is measured in units called decibels (dB). A decibel unit expresses the relative intensity of sounds on a scale from zero for the average least perceptible sound to about 100 dB, which is near the level most people find uncomfortably loud. Normal speech is around 50 to 60 dB. The following chart demonstrates the sound scale in decibels. When an individual is over-exposed to excessive loudness, sensitive structures of the inner ear, such as hair cells, can be damaged, causing noise-induced hearing loss (NIHL), a particular type of hearing loss.
Our perception of sound is directly related to the physical properties of sound waves (see Figure 3.7). One of the ï¬ rst things that we notice about a sound is how loud it is. Loudness is determined by the intensity, or amplitude, of a sound wave and is measured in units called decibels. Zero decibels represents the loudness of the softest sound that humans can hear, or the absolute threshold for hearing. As decibels increase, per-ceived loudness increases. Pitch refers to the relative âhighnessâ or âlownessâ of a sound. Pitch is determined by the frequency of a sound wave. Frequency refers to the rate of vibration, or number of waves per second, and is measured in units called hertz. Hertz simply refers to the num- ber of wave peaks per second.