Methods of Vision Screening of Employees

Two techniques for screening vision may be used:

1. Modified clinical technique (MCT);
2. Instrument screeners.

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New Eye Exam for Early Detection of Alzheimer's Disease

Researchers at the university of Minnesota Center for Drug Design have published a study in Investigative Ophthalmology and Visual Science in which a new technique was used to identify Alzeimer's disease in mice by simply taking pictures of their retinae with topical endoscope fundus modified with vision camera and tunable wavelength systems.

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Sides Effects of Ocular Laser Surgery

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The use of laser technology has increased greatly years and lasers have many applications in engineering, science, medicine and the defense industry. A laser beam is a monochromatic, coherent, parallel, very high energy beam.

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Side Effects of Radiations from Ophthalmic Instruments

Photo Credit: gettyimages

There is concern that radiation from ophthalmic instruments may cause damage to the eye being examined, especially the retina. The proceedings of a symposium on intense light hazards in ophthalmic diagnosis and treatment have shown that various ophthalmic instruments are capable of causing damage to the retina.

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Why Do Optometrists Measure Blood Pressure Of Their Patients

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The arguments favoring optometrists' measuring their patients' blood pressures were reviewed in Optometry Reconsidered Optom. Monthly, 1977. Many people, who would not regularly visit a physician, will visit an optometrist routinely for vision care.

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Vision Screening Of Employees

The general purpose of any vision screening programme is to detect those people who have defective vision but who do not present with symptoms that

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Steps in Optometry Case History Taking

A complete case history taking should be structured as;

1. Demographic Data.
2. Chief Complaints.
3. Ocular History.
4. Health history and Medication.
5. Family Eye History.
6. Family Medical History.

Demographic Data

Demographic data comprises of the following;

Name, address, phone number, age, gender, occupation, religion, marital status, hobbies etc.

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Methods Of Presbyopic Add Determination

Presbyopic add simply means the difference between the distance correction and the reading correction. When determining presbyopic add of an individual the optometrist should keep the following basic principles in mind;

• Find the distance error first and correct it.
• A suitable plus lens addition should be made over the distance correction to get the near correction.
• Near point should be fixed based on patient’s profession.
• Prescribe the weakest plus lens with which the patient sees clearly at near point since overcorrection will result in asthenopic symptoms.
• The near correction added should be such that about one-third (1/3) of the amplitude of accommodation should remain as reserve. In general, it is better to under-correct than to overcorrect presbyopia.

The following methods are used in determining presbyopic add;

Best Visual Acuity Subjective (Plus Build Up)

In this method, plus lenses are added binocularly above the patient’s subjective finding (#7) until he/she reads the smallest letters on the near point card placed at the customary working distance. The total lens in place is subtracted from the subjective finding to get the presbyopic add. This test can also be performed monocularly but the binocular method is preferred because the monocular method results in greater near addition due to lack of convergence accommodation.

Dynamic Retinoscopy

In this method, the preferred near working distance of the patient is used to perform the test and the plus lens that neutralizes the with-motion is taken as the tentative presbyopic add.

Bichrome Method                    

Testing monocularly, plus lenses are added until the red chart at near is clearer for each eye. Reduce the plus lens binocularly until the green chart is clearer and the plus lens remaining is the presbyopic add.

Based On Age

         Age                                                   Add

40 – 45 years                                          +1.00D

45 – 50 years                                          +1.50D

50 – 55 years                                          +2.00D

55 – 60 years                                          +2.50D

60 – 75 years                                          +3.00D

Based on Amplitude of Accommodation

Add = working distance in diopter – 1/2AA

i.e 100/d(cm) – 1/2AA

Example; Calculate the add of working distance 40cm if the patient has an amplitude of accommodation of +2.50.

Add = 100/40 – 1/2(2.50) = +1.25D

Cross Cylinder Method

The difference between the 14A net or 14B net finding (whichever is higher) and the distance correction is the reading add.

Example; #14A net = +4.00D, #14B net = +3.00D, #7 = +1.00D.

Add = +4.00 – 1.00 = 3.00D

Balancing PRA and NRA

Add = NRA – 1/2(PRA + NRA)

Example; Calculate add if positive relative accommodation is -0.50 and negative relative accommodation is +2.00.

Add = +2.00 – 1/2(0.50 + 2.00) = 0.75D

NOTE: This method is less accurate.

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Two Criteria For Determining Prisms

When prism is the only reliable and feasible treatment for a symptomatic heterophoric patient, you may apply these two methods.

Sheard’s Criterion

This states that for single clear binocular vision, the compensating fusional reserve should be at least twice the demand (phoria).

Mathematically, prism needed to satisfy sheard’s criterion =2(phoria) – compensating fusional reserve/3

Prism is only prescribed if the value gotten is in plus sign but if it is in minus sign, then prism is not needed.

Take note of the following;

For exophoria, base-out to blur finding (16A)

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How To Determine The AC/A Ratio Of A Patient

AC/A ratio is the accommodative-convergence that follows one diopter of accommodation. The normal AC/A ratio is 4/1 which means; for every +1.00 of accommodation, 4prisms of accommodative-convergence is being exerted. However, the normal value of AC/A ratio also ranges from 4/1 to 6/1.

The function of accommodation is to obtain a clearer focus while that of convergence is to obtain a single binocular vision. Accommodation is able to stimulate a definite amount of convergence (Accommodative convergence). If the influence of accommodation is excessive, it may produce a manifest deviation (esotropia) whereas if the influence is low (low AC/A ratio) and fusional convergence is inadequate, the individual may have exotropia.

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Ocular Complications and Side Effects of Topical Steroid Eye Drops

Corticosteroids are important therapeutic agents that are used to treat ocular inflammation. Their complications are related to dosage and duration of therapy because usually, no serious adverse effect is observed

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