Difference between Myopia (Near Sightedness) & Hyperopia (Far-Sightedness)

0:00Difference Between Myopia (Near-sightedness) and Hyperopia (Far-sightedness)

0:02MYOPIA

0:04Origin of the word

0:06It comes from the Greek word muōps,

0:08meaning short-sighted

0:10these people cannot see distant objects clearly.

0:13Anatomy

0:15Before we describe myopia,

0:17let’s compare the eyeball to a camera

0:19for better understanding.

0:21When we take a picture,

0:23light after reflecting from an object

0:25enters the camera

0:26and passes through following;

0:28Firstly, it passes a transparent glass

0:31in front of the aperture of the camera.

0:33Then secondly,

0:34it passes a camera lens

0:36that helps us in focusing light rays

0:38and lastly,

0:39there is a camera film on which light is focused

0:41for a clear picture.

0:43Eye is somewhat similar as when we see an object,

0:47light after reflection from that object

0:49enters our eye through;

0:51Firstly,

0:51it passes cornea,

0:53the transparent curved front part of the eye,

0:56then secondly,

0:57it passes through the crystalline lens

0:59that helps us in focusing light rays

1:01and lastly,

1:02there is the retina,

1:04light sensitive receptor cells

1:06in the posterior part of the eyeball

1:08on which light is focused for a clear image.

1:11Definition of Myopia

1:13It is a form of refractive error,

1:16inability to refract, bend,

1:18focus the light rays properly

1:20in which parallel rays of light

1:22i.e. coming from a distinct object,

1:24after entering the eye,

1:26are focused in front of the retina

1:28instead of on retina

1:29with eye muscles at rest.

1:32Causes:

1:331. Curvature

1:35increase of curvature of cornea or lens

1:38causes light rays to be focused in front of retina

1:41and hence Myopia occurs.

1:432. Axial

1:44increase in axial length of eye,

1:46increases the converging power

1:48and cause light rays to be focused in front of retina.

1:523. Index

1:53increase in refractive index

1:56i.e. light bending/focusing power of the lens

1:59for example in cataract.

2:014. Positional

2:03anterior displacement of lens e.g. after trauma.

2:07This again causes light rays

2:09to be focused in front of retina.

2:11Types

2:121. Congenital : from birth.

2:152. Simple: most common,

2:17starts from 5-10 years till 15-20 years

2:20and is mostly due to curvature

2:22or length problem of eyeball.

2:243. Pathological:

2:25hereditary, progressive

2:27and is due to degenerative changes in the eyes.

2:32Clinical features - Symptoms

2:34- Blurred vision

2:36- Half shutting of eyes (parents of child will tell);

2:39- Outward deviation of eye (Divergent squint).

2:43Normal patients require to move their eyes inward

2:46while focusing near objects.

2:48This is not required in Myopic patients

2:51causing their eye to move out

2:53intermittently or constantly.

2:55Signs:

2:561. Prominent eye ball as eye is big

2:592. Retinal changes in pathological Myopia

3:04Diagnosis:

3:061. Retinoscopy:

3:08a hand-held device that throws light in the eye

3:10and allowing us

3:11to observe its movements and reflection,

3:13hence helping to confirm the refractive error.

3:162. A-scan:

3:18a small ultrasound probe

3:20that throws ultrasound waves in the eye ball

3:22and then detects their reflections

3:24or echo timings,

3:25calculating the eye ball length.

3:29Treatment:

3:30Unlike the camera,

3:31maximum (2/3rd) focusing in an eye

3:35is done by the transparent front part (cornea),

3:38while the rest (1/3rd) is done by the lens.

3:41So,

3:42while treating these patients,

3:44we have to decrease the focusing power of the eye

3:46so that the image is formed on the retina

3:48instead of in front of it.

3:50This can be done

3:51by using either a diverging lens like:

3:54Glasses,

3:58contact lenses,

4:03or some surgical procedure.

4:06Surgical Treatment:

4:07Flattening the central part of cornea.

4:10This include different methods

4:12that were changed and advanced

4:14depending upon reduction of side effects,

4:16recovery time and improvement of degree of vision.

4:19The surgeries included in this category are:

4:22Radial keratotomy,

4:24Photorefractive keratectomy,

4:27LASEK: Laser Epithelial Keratomileusis,

4:31LASIK: Laser In-situ Keratomileusis.

4:37Other Surgical Treatment options are:

4:39Lens extraction

4:41Contact lens implantation.

4:45HYPEROPIA

4:48Anatomy

4:49Before we can describe hyperopia,

4:52let’s compare the eye ball to a camera

4:54for better understanding.

4:56When we take a picture,

4:58light after reflecting from an object

5:00enters the camera and passes through;

5:03First, a transparent glass

5:05in front of the aperture of the camera

5:07then secondly,

5:08a lens that helps us in focusing light rays

5:11and lastly,

5:12a film on which light is focused

5:14for a clear picture.

5:16Eye is somewhat similar,

5:18as when we see an object,

5:20the light after reflection from that object

5:22enters our eye through;

5:24Firstly,

5:26cornea: the transparent curved front part of eye,

5:29then secondly,

5:31through the crystalline lens

5:32that helps us in focusing the light rays

5:35and lastly,

5:36the retina:

5:37light sensitive receptor cells

5:39in the posterior part of the eye ball

5:41on which light is focused for a clear image.

5:44Definition of Hyperopia

5:47It is a form of refractive error

5:50inability to refract, bend,

5:52focus the light rays properly

5:54in which parallel rays of light

5:56i.e. coming from a distinct object

5:59after entering the eye

6:00are focused behind the retina

6:02with accommodation (eye muscles) at rest.

6:06Key features

6:07This refractive error has three key features:

6:11Image is formed behind the retina,

6:13in normal people

6:14image has to be focused on the retina

6:16for it to be clear.

6:18Parallel light rays,

6:20the rays that only come from objects

6:21at 6 meters or beyond,

6:23must be used for assessment.

6:25As when objects come closer than 6 meters,

6:28light rays start to diverge,

6:30changing their focus.

6:32This is why we place Snellen’s chart at 6 meters.

6:36Eye must be at rest.

6:38Just like a DSLR camera’s focusing power can be changed

6:42by rotating its zoom lens,

6:44eye changes its focusing power

6:46by changing the shape of its lens

6:48with the help of contraction

6:50and relaxation of certain muscles

6:52located inside the eye ball.

6:54These muscles must be at rest

6:57to correctly access the eye’s focusing power.

7:00This is also the reason why we use cycloplegic

7:03or muscle paralyzing drops

7:05before estimating the amount of refractive error.

7:08Misnomer

7:10Both hyperopia and myopia

7:12have abnormal distant vision

7:14i.e. they cannot focus distant objects clearly.

7:18But a unique thing about hyperopia

7:20is that if these patients

7:22increase the power of their lens,

7:24by contraction of certain intraocular muscles,

7:27they can focus the image

7:28accurately on their retina.

7:30This will result in excessive

7:32and continuous use of intraocular (ciliary) muscles

7:36in order to keep the image focused on the retina,

7:39resulting in pain.

7:40Also,

7:41when they try to see near objects,

7:44their eyes will require

7:45even more focusing power

7:47which these muscles can no longer provide

7:50hence causing near objects to become blurry.

7:53So,

7:54a lot of hyperopic patients (not all),

7:57with less degree of hyperopia,

7:59will say that they see distant objects clearly

8:02but they have pain/discomfort in their eyes

8:05or their eyes get tired

8:06and also near vision is mostly not that good.

8:10Hence,

8:10these patients are mistakenly called far sighted.

8:14Causes

8:151. Curvature:

8:17curvature of cornea or lens is flatter than normal.

8:212. Axial:

8:23short axial length of eye.

8:263. Index:

8:29decrease in refractive index

8:31i.e. light bending/focusing power of the lens

8:36e.g. in cortical cataract.

8:384. Positional:

8:40posterior displacement of lens e.g. after trauma.

8:455. Aphakia:

8:47absence of lens in eye,

8:48therefore eye cannot focus light rays on retina.

8:52Types

8:531. Total hyperopia

8:56it is the total refractive error

8:58calculated after complete cycloplegia,

9:01intraocular muscle paralysis,

9:04induced by certain drops.

9:062. Latent hyperopia

9:09amount of hyperopia

9:11corrected by the focusing power produced

9:13due to normal tone of intraocular (ciliary) muscles.

9:17It is usually 1 diopter.

9:203. Manifest hypermetropia

9:23It is the remaining portion of hyperopia,

9:26divided into:

9:27- Facultative

9:29amount of hyperopia

9:30corrected by the focusing power produced

9:33due to active contraction of ciliary muscles.

9:36- Absolute

9:37amount of hyperopia that cannot be corrected

9:41even by contraction of ciliary muscles.

9:44Clinical Features

9:46Symptoms

9:47Eye straining or discomfort

9:49asthenopia,

9:51including : eye tiredness,

9:53pain, headache or mild photophobia.

9:57Blurred vision with eye straining:

10:00when muscle contraction attempts

10:02but fails to correct hyperopia.

10:05Blurred vision only:

10:07when refractive error is high

10:09and cannot be corrected at all

10:11by muscle contraction efforts.

10:13Inward deviation of eye,

10:15convergent squint,

10:17normal patients require to move their eyes inward

10:21while focusing near objects

10:23this is enhanced in hyperopic patients,

10:26causing their eye to move inwards

10:28intermittently or constantly.

10:30Signs:

10:31small eye ball,

10:33corneal diameter may be small.

10:35Retinal exam might show false changes

10:38due to distortion of image

10:40when hyperopia exceeds 5 diopters.

10:43Diagnosis

10:451. Retinoscopy:

10:46a hand-held device that throws light in the eye

10:50and allowing us

10:51to observe its movements and reflection,

10:53hence helping to confirm the refractive error.

10:572. A-scan:

10:58a small ultrasound probe

11:00that throws ultrasound waves in the eye ball

11:03and then detects their reflections

11:05or echo timings,

11:06calculating the eye ball length.

11:09Note:

11:10At birth all eyes are hyperopic

11:13+2.5 to +3 diopters,

11:17i.e. light is focused behind the retina.

11:20As the eye ball grows

11:22and at about 6-7 years age

11:24eye ball is of normal size

11:26and light is now focused on the retina or emmetropic.

11:31In some people

11:32it continues to grow causing myopia

11:35or light is focused in front of retina.

11:38Treatment

11:39Unlike the camera,

11:41maximum (2/3rd) focusing in an eye

11:44is done by the transparent front part (cornea),

11:47while the rest (1/3rd) is done by the lens.

11:51So, while treating these patients

11:53we have to increase the focusing power of the eye

11:56so that the image is formed on the retina

11:58instead of behind it.

12:00This can be done by using either a converging lens

12:04e.g. non-surgical treatment.

12:07Glasses,

12:08contact lenses,

12:09or some surgical procedure.

12:12Surgical Treatment

12:15Making the central part of cornea more curved.

12:18This include different methods

12:20that were changed and advanced

12:22depending upon reduction of side effects

12:24and recovery time

12:26and improvement of degree of vision.

12:28PRK, Photorefractive keratectomy:

12:32Remove corneal epithelial cells

12:35by a solution

12:37then use laser to reshape cornea

12:40i.e. making it steeper

12:42and then apply a bandage contact lens.

12:45Side effects include pain

12:47and recovery is in 1 week at least.

12:50It corrects 2 Diopter hyperopia.

12:53LASIK, Laser In-situ Keratomileusis:

12:58corrects up to 4 Diopter.

13:01A famous and frequently performed surgery nowadays.

13:04In this procedure

13:06a device, keratome, slice a flap of cornea,

13:10160 micrometer,

13:12laser is applied to change the corneal shape

13:15and then the flap is repositioned.

13:17Advantages

13:19Advantages over other procedures

13:22Absence of post-operative pain,

13:24More rapid visual rehabilitation.

13:27Conductive keratoplasty:

13:30it involves giving radiofrequency energy

13:33to corneal stroma

13:35causing change in its shape.

13:37Can correct low to moderate hyperopia.