Ridley’s implantation (1949) of the first intraocular lens (IOL) marked the beginning of a major change in the practice of ophthalmology. The IOLs are microlenses placed inside the human eye to correct cataracts, nearsightedness, farsightedness, astigmatism, or presbyopia. There are two types of IOLs: anterior chamber lenses,which are placed in the anterior chamber of the eye between the iris and the cornea, and posterior chamber IOLs, which are placed in the posterior chamber behind the iris and rest against the capsular bag. Procedures for implanting the IOLs and technologies for manufacturing them in various sizes, thicknesses, and forms as well as with various materials progressed tremendously in the last decade. Multifocal IOLs are one of the important signs of this progress. While monofocal IOLs, the most commonlyused, are designed to provide clear vision at one focal distance, the design of multiple optic (multifocal) IOLs aims to allow good vision at a range of distances.
Both Light and Sound Have Oscillating Waves
|Velocity||Travels Through Vacuum?||Wavelength||Frequency|
|Yes||400-700 nm||4 X 10^14
to 7 X 10 ^14
|Sound||About 700 mph
(about 340 m/sec)
(1 mile per 5 seconds)
|No||.02 to 20 meters||20-20,000 cycles/sec|
- Sound and light are waves in which the amplitude oscillates with time
- For pure tones or colors the oscillation is a sine wave with a fixed wavelength and frequency
- The wavelength is the distance between 2 peaks of the wave
WHAT IS TONOMETER?
THIS PARAGRAPH HAS BEEN WRITTEN IN REFERENCE TO MDU ROHTAK EXAM PATTERN
In order to ensure a person’s optic nerves are healthy, optometrists check the pressure placed on them by the fluid in the eyes. This pressure is called intraocular pressure and should measure between 10 mmHg and 21 mmHg. Measurements that are higher than normal can be a sign of early glaucoma or retinal detachment.
A Snellen chart is an eye chart used by eye care professionals and others to measure visual acuity. Snellen charts are named after the Dutch ophthalmologist Herman Snellen who developed the chart in 1862
The traditional Snellen chart is printed with eleven lines of block letters. The first line consists of one very large letter, which may be one of several letters, for example E, H, N, or A. Subsequent rows have increasing numbers of letters that decrease in size. A patient taking the test covers one eye, and reads aloud the letters of each row, beginning at the top. The smallest row that can be read accurately indicates the patient’s visual acuity in that eye.