Retinometer (synonym: interferometer) is a diagnostic instrument used in ophthalmology (eye care). It measures the resolving power of the retina (retina in the eye) using interference patterns generated by two laser light sources.
The retinometer is used to determine the so-called potential visual acuity (visual acuity) in patients suffering from cataract (cataract) or other opacities of the optical media of the eye. The optical media of the eye are considered to be the lens, vitreous body and cornea. Usually, a patient’s visual acuity is tested using a subjective visual acuity determination, but if there is an opacity, for example, of the lens, the result of such a test may be falsified, as correct information is often not possible from the patient. The retinometer allows determination of potential visual acuity, that is, visual acuity as it would exist if the optical apparatus of the eye were intact.
Indications (areas of application)
Determination of potential visual acuity in the presence of opacification of the optical media of the eye for:
- Determination of an indication for surgery, e.g., for cataract, or the possibility of visual acuity improvement after removal of the opacity.
- Differential diagnostic clarification of other causes of visual acuity reduction, e.g., optic nerve disorders.
Contraindications
In this examination, if the optical media is cloudy, pupil dilatation (pupil dilation) using mydriatics (pupil dilating drug) is necessary. Contraindications to the use of these drugs are:
- Narrow-angle glaucoma (glaucoma; increase in intraocular pressure due to an obstruction in the outflow of aqueous humor).
The procedure
The retinometer works on the principle of so-called Maxwell imaging. Bypassing the optical apparatus so that the media opacity does not cause interference, a stimulus is projected into the eye through a small transparent gap, for example, in the opacified lens (cataract). With the help of this stimulus, the visual acuity test can be performed: A laser or other light source images a grid pattern on the retina through the gap, which can vary in orientation and brightness. Visual acuity corresponds to the resolution acuity of the finest grid that can just be detected by the patient. The potential visual acuity or retinal visual acuity is determined. In the presence of severe media opacities, the accuracy of the method’s prediction decreases.
The examination should be performed in dim light, and maximum dilation (dilatation by eye drops containing so-called mydriatics) of the pupils is also necessary. The patient must be informed that he/she will not be able to drive afterwards. Furthermore, examination of the better-seeing eye is recommended first to accustom the patient.
Possible complications
The possible complications also arise from the use of mydriatics:
- Inducing epileptic seizures (rare).
- In children and premature infants: In rare cases, risk of paralytic ileus (disruption of intestinal passage due to loss of natural bowel movement).
- Fatigue
- Peripheral vasodilation (dilation of terminal blood vessels, e.g., of the hands).
- Tachycardia (rapid heartbeat).
- Restlessness and disorientation
Benefit
By using retinometer examination, cataract surgery can be advised in many cases. If there is evidence that visual acuity will not increase after surgery, unnecessary surgery can also be avoided. The certainty of your cataract decision is increased by the retinometer.