There are three basic elements that one would need to consider to be able to formulate a diagnosis of error of refraction.
1. History – a comprehensive history is an important component of a work up for error of refraction.
2. Ocular Examination – basic eye examination comprised of the following parts should be done on each patient.
Gross eye examination – slit lamp examination
Visual acuity testing
Intraocular pressure determination
Movement of Extraocular muscles
Funduscopic Examination
3. Ancilliary Examinations – manual or automatic refraction is an examination routinely performed to determine the presence and type of error of refraction. Other special examinations may include biometry, keratometry and corneal topography.
Each of these aspects will be discussed subsequently.
HISTORY TAKING IN A PATIENT WITH ERROR OF REFRACTION
Extracting the history from a patient with probable error of refraction can be very useful. The patient’s history guides the clinician in arriving at a complete diagnosis, particularly as to the possible type of error of refraction. Furthermore, the history can provide the clinician with an idea as to the visual needs of the patient and the appropriate treatment modality. The clinician should ask each and every patient suspected to have an error of refraction the following questions.
Answers to the following questions serve as aids in the formulation of a complete diagnosis.
1. What is your patient’s chief complaint?
The most common presenting complaints of patients with errors of refraction include blurring of vision for distance, for near, or both. Clear near vision but blurred distance vision indicates near sightedness or myopia.. Hyperopics (far sighted individuals) may complain of early visual fatigue when performing visual tasks (especially at near). Headache especially after prolonged eye use is common with hyperopics and astigmatics but non-specific and will have to be differentiated from other causes.
2. How long has this problems been going on?
The duration of the problem should be extracted from the patient. Errors of refraction usually present with a prolonged history of their complaints. Whether it is recurrent or progressive should also be noted.
One should be aware of a condition of middle age called presbyopia where the lens of the eye gradually loses its ability to focus at near objects.
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3. Which eye is involved?
Does the problem involve one eye or both eyes? Significant difference of refraction between the two eyes may be the cause of amblyopia or a lazy eye.
4. Are there other associated eye problems?
Elicit from the patient whether or not there is any history of redness, ocular pain, glare or photophobia, trauma or any form of eye surgery in the past.
5. Does the patient have any prior consultations?
One should be able to determine a patient’s previous correction of his/her error of refraction to help determine the course of the condition.
6. Other aspects of the patient’s history that should be considered include:
Family History. Is there a history of any similar illness in the family? Genetic factor strongly determine refractive errors of the eye. Is there any history of any hereditary illness like diabetes?
Changing blood sugar levels may affect a person’s refraction.
Social History. What is the patient’s occupation? What are the patient’s usual visual tasks?
Medical History. Has the patient suffered any form of illness in the past particularly diabetes? Is she under any form of medication for any illness? These may affect vision.
OPHTHALMOLOGIC EXAMINATION OF THE PATIENT
The basic tools that one would require in conducting an examination of the patient with suspected error of refraction include the following:
♦ Visual acuity charts – both for distance and near vision
♦ Occluder with pin-hole
♦ Penlight – for gross examination of the eye
♦ Ophthalmoscope – used for fundus examination
COMMON OCULAR FINDINGS IN AMETROPIA
Typically, the patient with error of refraction will present with the following findings:
1. Visual Acuity. As has been mentioned earlier, most patients with would present with reduction in vision either for far, near, or both. Snellen charts are commonly used for distance vision testing and Jaeger or Snellen equivalent cards for near vision. If the vision improves when the patient looks through the pin-hole, the patient most probably has an error of refraction that can be corrected with lenses.
2. Intraocular Pressure. Most patients would typically present with normal intraocular pressures
3. Extraocular Muscle Movement. The extraocular muscles are usually not involved in errors of refraction and a majority of patients will exhibit full movement on all directions of gaze. Some forms of
heterophoria or heterotropia are associated with errors of refraction.
4. Funduscopic Findings. Patients wherein the error of refraction is not severe will present with normal findings. In cases where the eyeball is elongated the fundus and optic nerve head may exhibit some changes
5. Retinoscopy will reveal the following findings:
“With” movement of reflex with the streak is seen in hyperopia and small myopias, “against” movement in myopia.
Retinoscopy has achieved neutrality in A but still ‘with’ in B, indicating different refracting powers in the two meridia, a sign of astigmatism.
ANCILLARY EXAMINATIONS
Commonly, additional examinations may be requested to aid in the diagnosis of some conditions. The more commonly requested ancillary procedures include:
1. Keratometry
The keratometer is an instrument that can measure central anterior corneal curvature. It can be used to check the type and amount of astigmatism. It is also used in fitting contact lenses, a form of correction for errors of refraction.
2. Corneal Topography
It is a sophisticated instrument that produces a color-coded topographic map of the cornea that shows the pattern of the corneal curvature. It usually functions as a keratometer as well, measuring corneal curvatures.
It demonstrates irregularities of curvature like keratoconus.
3. Biometry
This instrument using sound waves provides measurement of the axial length of the eyeball, a determining factor of the refractive condition of the eye.
REVIEW QUESTIONS: PART I & II
1. Error of refraction or ametropia refers to a condition where A. light rays are blocked from the retina
B. light rays from a source more than 6 meters from an eye at rest do not focus on the retina
2. In error of refraction a presenting symptom
A. may be blurred distance vision, near vision, or both.
B. is color aberration.
C. is nasal scotoma
3. Intraocular pressure in plain errors of refraction is usually A. normal
B. high C. low 4. Error of refraction has
A. No hereditary pattern B. Strong genetic influence 5. Retinoscopy is
A. the same as funduscopy
B. an objective means of measuring errors of refraction
C. a means to take retinal photographs to determine retinal changes due to errors of refraction 6. If the poor vision of a patient improves when viewing the test chart through a pin-hole
A. it is the pupil that is at fault B. there may be error of refraction C. dark glasses are the cure 7. Measurement of refractive errors
A. cannot be done by machines B. is usually very subjective
C. can be performed using automatic refractors 8. In middle age, one may
A. gradually lose the ability to focus for near or presbyopia B. usually develop myopia
C. usually develop hyperopia
9. Normal or emetropic eyes looking at an object 20 or more feet away A. need to accommodate to focus light on the retina B. need to squint to focus light on the retina
C. should be able to see appropriate sized Snellen letters with the eye at rest 10. If a diabetic consults for sudden blurring of vision after a rise in sugar level
A. it is part of the aging process for diabetics
B. the refractive state of the eye may have been affected by the sugar level C. it is surely diabetic retinopathy
D. keratometry will demonstrate the changes in corneal curvature due to sugar levels
PART III. CLASSIFICATION OF AMETROPIAS (ERRORS OF REFRACTION AND