Almost all causes of visual impairment can be classified into five categories. These are:

Visual Acuity

Visual acuity is the "sharpness of vision." The most common way to measure visual acuity is through the Snellen measurement by which you will have seen as a fraction (20/20). The top number indicates the distance that an object is able to be seen at by a person with good acuity (20 feet away to measure distance; 16 inches away to measure near). The visual acuity measure tells us how clearly a person is able to perceive visual targets. The bigger the lower number gets, the worse vision is.

Myopia=Nearsightedness *Can't see distance
- - The image is focused before it reaches the retina; Requires a concave lens which is minus to subtract diopters.
Hyperopia=Farsightedness *Can't see near
- - The image is focused after it reaches the retina; Requires a convex lens (thick) which is a plus to add diopters

Presbyopia=Vision loss due to age
- - Requires a bifocal to add diopters
Astigmatism=Out of focus
- - Irregularly shaped cornea that causes blurred vision; Requires specialty lens
Presbyopia
- - Lens loses flexibility with age; Requires a bifocal

Visual Field

The visual field refers to the total area by which objects can be seen in the peripheral vision when you focus your eyes on a central point. Most people are able to see between 170-180 degrees from their left shoulder to their right when they are looking straight ahead.

Central Field is clearer than peripheral field (sides)
Scotomas are blind spots anywhere within the visual field area
A field loss can result from damage to any part of the visual pathway

Binocularity

Binocularity refers to the ability to focus on an object with both eyes and create a single stereoscopic image. That is, we see things in three dimensions; things have height, depth, and width. The muscles of the eye are primarily responsible for making binocularity possible.

Esotropia
- - Turning in, toward the nose
Exotropia
- - Turning out, toward the temple
Hypotropia
- - Turns downwards
Hypertropia
- - Turns upwards

Color Perception

Color perception is the ability to see and distinguish colors. This function is performed by specific cells in the retina. A deficit in color perception, something referred to as color blindness, tends to have the least impact on an individual's daily life. There is no treatment.

Processing Problems

Vision loss due to damage to the visual association areas of the brain; The current leading cause of VI in children.

Eye Conditions

Congenital Cataracts

Download Eye Condition Fact Sheet Here

Pediatric Cataract Surgery 2nd Edition

visual showing the difference between a normal lens and a clouded lens

img: http://www.eyetrustclinic.com/cataract.php

Cortical Visual Impairment

Wbsites & Handouts

What to include in an IEP for a Student who has CVI>> Paths to Literacy
What is Cortical Visual Impairment>>Little Bear Sees
Characteristics of CVI In Children >> compiled by Dr. Dixie Mercer, SFASU

Encouraging Efficient Use of Vision in Students with CVI >>by Diane Sheline

Strategy To See >> Diane Sheline's Website

CVI Tips for Home & School

Specific Tips for Enhancing the Visual Functioning of Children Who Have CVI Throughout the Day

The APH (American Printing House) CVI Webpage

link to perkins elearning article on cortical visual impairments

img: https://www.perkinselearning.org/videos/webcast/cortical-visual-impairment-and-evaluation-functional-vision

Glaucoma

Guide to Glaucoma: Find the causes, symptoms, and treatment

American Academy of Ophthalmology: What is Glaucoma?

Mayo Clinic: Glaucoma

Oculocutaneous Albinism

Download Eye Condition Fact Sheet Here

American Academy of Ophthalmology: What is Albinism?

WebMD: What is Ocular Albinism?

VisionofChildren.org What is Ocular Albinism?

Optic Nerve Hypoplasia

Download Eye Condition Fact Sheet Here

National Organization for Rare Disorders: Optic Nerve Hypoplasia

facts on septo-optic dysplasia. 30% have optic nerve defect, brain, and pituitary gland malformation. 60% have abnormal endocrine function. 40% have normal endocrine function

img: https://villa-medica.com/septo-optic-dysplasia-and-cell-therapy/

Retinoblastoma

Retinoblastoma is a rare type of eye cancer that usually develops in early childhood, typically before the age of 5. This form of cancer develops in the retina, which is the specialized light-sensitive tissue at the back of the eye that detects light and color.

In children with retinoblastoma, the disease often affects only one eye. However, one out of three children with retinoblastoma develops cancer in both eyes. The most common first sign of retinoblastoma is a visible whiteness in the pupil called "cat's eye reflex" or leukocoria. This unusual whiteness is particularly noticeable in dim light or in photographs taken with a flash. Other signs and symptoms of retinoblastoma include crossed eyes or eyes that do not point in the same direction (strabismus), which can cause squinting; a change in the color of the colored part of the eye (iris); redness, soreness, or swelling of the eyelids; and blindness or poor vision in the affected eye or eyes (NIH, 2020).

American Cancer Society: Retinoblastoma

Children's Cancer Aid and Research Center: Retinoblastoma

NIH: Retinoblastoma

Retinopathy of Prematurity

Retinopathy of prematurity (ROP) is a potentially blinding eye disorder that primarily affects premature infants weighing about 2¾ pounds (1250 grams) or less that are born before 31 weeks of gestation (a full-term pregnancy has a gestation of 38–42 weeks). The smaller a baby is at birth, the more likely that baby is to develop ROP. This disorder — which usually develops in both eyes — is one of the most common causes of visual loss in childhood and can lead to lifelong vision impairment and blindness. ROP was first diagnosed in 1942.

American Academy of Ophthalmology: What is ROP?

National Eye Institute: Retinopathy At a Glance

Kids Healthy: ROP