Eye power, also known as refractive power, is calculated based on the refractive error of your eyes. This error can include myopia (nearsightedness), hyperopia (farsightedness), astigmatism, and presbyopia (age-related difficulty focusing on close objects).

Here’s how it’s calculated:

1. Visual Examination: An optometrist or ophthalmologist conducts a visual examination to assess your vision and identify any refractive errors.

2. Refraction Test: During a refraction test, you’ll look through a series of lenses while reading an eye chart. The doctor will ask which lenses make your vision clearer. This helps determine the amount of correction needed for your vision.

3. Retinoscopy: In this test, the doctor shines a light into your eye and observes the reflection off the retina while changing lenses. This provides an objective estimate of your refractive error.

4. Autorefraction: Some clinics use automated instruments to measure your refractive error quickly.

5. Keratometry: For astigmatism, the curvature of the cornea is measured using a keratometer.

6. Prescription: Based on the results of these tests, the doctor determines your prescription, which is measured in diopters (D) for each eye. For example +1.5 D means you have hypermetropia with 1.5 eye power. -2.5 D represents myopia with 2.5 eye power.This prescription indicates the strength of lenses needed to correct your vision to normal levels.

The prescription includes three main components:
– Sphere (Sph): Indicates the lens power needed to correct nearsightedness or farsightedness.
– Cylinder (Cyl): Indicates the lens power needed to correct astigmatism.
– Axis: Specifies the orientation of the cylinder for astigmatism correction.

Some other terms used:
O.S.
Oculus sinister denotes the left eye also prescribed as LT.

O.D.
oculus dextrus which represents the right eye also prescribed as RT.

Plus(+) sign before the numbers in your prescription indicates farsightedness or hypermetropia/ hyperopia.

(-) minus sign indicates near/shortsightedness or myopia.

Once your eye power prescription is determined, you can use it to get glasses, contact lenses, or undergo refractive surgery if suitable.

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There are several types of eyeglass lenses designed to correct different vision problems and cater to various needs:

1. **Single Vision Lenses:** These lenses have a single prescription power throughout the entire lens and are used to correct nearsightedness, farsightedness, or astigmatism.

2. **Bifocal Lenses:** Bifocal lenses have two distinct optical powers: one for distance vision and one for near vision. They have a visible line separating the two powers.

3. **Trifocal Lenses:** Trifocal lenses have three distinct optical powers: for distance, intermediate, and near vision. They also have visible lines separating the powers.

4. **Progressive Lenses:** Progressive lenses, also known as no-line bifocals or multifocal lenses, provide a smooth transition between multiple focal points, offering clear vision at all distances without visible lines.

5. **Photochromic Lenses:** These lenses darken when exposed to sunlight and become clear again indoors. They provide both vision correction and UV protection.

6. **Polarized Lenses:** Polarized lenses reduce glare from reflective surfaces like water, snow, and roads, improving visual comfort and clarity, especially in bright sunlight.

7. **High-Index Lenses:** High-index lenses are thinner and lighter than standard lenses, making them a good choice for people with higher prescriptions who want thinner, more aesthetically pleasing glasses.

8. **Aspheric Lenses:** Aspheric lenses have a flatter, slimmer profile than traditional spherical lenses, reducing distortion and providing a wider field of view, especially in higher prescriptions.

The Tamil calendar, also known as the Tamil Panchangam, is a traditional calendar system followed by Tamil-speaking people, particularly in Tamil Nadu, India, and by Tamil communities around the world. It is primarily a solar calendar, with some lunar influences. Here’s a basic overview of how it’s calculated:
In the Tamil Calendar, the days correspond to the celestial bodies in the solar system, beginning with Sunday and continuing with the sequence: Sun, Moon, Mars, Mercury, Jupiter, Venus, and Saturn.Sunday (ஞாயிறு), Monday (திங்கள்), Tuesday (செவ்வாய்), Wednesday (புதன்), Thursday (வியாழன்), Friday (வெள்ளி), and Saturday (சனி)

In the Tamil calendar, which commences around April 14 of the Gregorian calendar annually, there are twelve months, each with a variable number of days ranging from 29 to 31.
Chithirai (சித்திரை)Vaikaasi (வைகாசி)Aani (ஆனி)Aadi (ஆடி)Aavani (ஆவணி)Purattaasi (புரட்டாசி)Aippasi (ஐப்பசி)Karthigai (கார்த்திகை)Maargazhi (மார்கழி)Thai (தை)Maasi (மாசி)Panguni (பங்குனி)

In the month of Aani, the sun’s northward journey, known as Uttaraayana Kaalam, reaches its conclusion. Since the sun traverses the Gemini zodiac sign during this time, it is called the month of Mithuna or Joshṭa in northern languages. Aani is considered a significant month in the Tamil calendar, consisting of 32 days.