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Dark room procedures for Ophthalmology Practicals: Part 2

Author: rxpg, Posted on Monday, August 04 @ 00:00:00 IST by rxpg  

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Ophthalmology

The use of Cycloplegia in retinoscopy

In retinoscopy a common source of error is accommodation which is most active in young patients. When patient accommodates the refractive power of the eye increases resulting in a variable shift towards myopia. A simple solution would be to relax the accommodation by the use of a cycloplegic but cycloplegia leads to abolition of basal tone of the ciliary body muscles resulting in manifestation of latent hypermetropia. So if the patient accommodates there is a shift towards myopia, and if we use cycloplegia there is a shift towards hypermetropia; however, the latter situation is preferable as the amount of shift towards hypermetropia caused by a given cycloplegic is known and the same amount can be reduced from the retinoscopy value to get the refractive error.



Cycloplegic-Mydriatic Agents

Preparation

Dosage

Age Group of patient

Amount to be reduced

Duration of action

Complication

1. Atropine sulfate 1 % oint.

TDS ΄ 3 days 0 to 5 years 1.0 to 1.5 D 2 to 3 weeks Allergy, Fever, Flushing of face, etc.

2. Homatropine hydrobromide 2 % drops

every 15 min. ΄ 4 applications 5 to 7 years 0.5 to 1.0 D 24 to 48 hr. Dry mouth, Urine retention in old

3. Cyclopentolate HCl 1% drops

every 15 min. ΄ 4 applications 7 to 20 years 0.5 to 1.0 D 12 to 24 hr. Transient psychotic reaction

4. Tropicamide 0.5-1 % drops

every 15 min. ΄ 4 applications not specified 0.25 to 0.5 D 2 to 4 hr. Dry mouth

5. Phenylepherine HCl 5-10 % drops

every 15 min. ΄ 4 applications where only mydriasis is required Nil (it has no cycloplegic action) 6 to 8 hr. Increase in BP in hypertensives

NB- For patients of 20 to 30 years of age cycloplegia is used if needed in a particular case, and after the age of 30 years cycloplegia is not required.

When retinoscopy is done under cycloplegia, patient is not prescribed glasses at the same time but patient is examined again after the effect of the cycloplegic has worn off i.e. usually after 1 week, for subjective verification (post cycloplegic test). However, patient’s acceptance of the refractive correction is determined the same day. Therefore, the sequence of steps of refraction are:

  1. Retinoscopy under cycloplegia.
  2. Get the acceptance by adding -1Έ distance (m). If the distance is 1 m then add -1Έ 1 i.e. -1.0
  3. Prescibe after cycloplegia is worn off by reducing from above value the amount for given cycloplegic used.

Note that the amount for cycloplegia is reduced only form the spherical component of the refractive correction.

II. Distant Direct Ophthalmoscopy (DDO) at 22 cm using plane mirror

After preliminary examination at 1 m examiner moves closer to the patient to a comfortable near vision distance of 22 cm (or 25 cm and concave mirror according to some authors). In a normal eye with clear media one can see red fundal glow in the pupil. The abnormalities that can be observed by this method are as follows:

  1. Opacity in the media (cornea, aqueous, lens and vitreous) will appear black against the background of red fundal glow. The opacity appears black because no light goes in the eye or comes out of it from the area of opacity.

  2. Depth of opacity (Parallactic Displacement) can be estimated qualitatively by the method of parallactic displacement. While observing the pupil patient is asked to move the eye up, down, right and left. An opacity located in the pupillary plane does not seem to move relative to the pupil whereas any opacity anterior to the pupil seems to move in the same direction and an opacity posterior to the pupil seems to move in opposite direction. The further away an opacity is from the pupillary plane the more does it move in relation to the pupil. This can be easily understood by studying the diagram above. If we take a rod which is hinged at point 3, and turn it up. The points 1 and 2 which are in front of the hinge move in the same direction and points 4 and 5 behind the hinge move in the opposite direction, whereas the point 3 which is in the plane of the hinge does not seem to move. When looked at end-on it appears like the figures on the right with the circles representing the pupil. The pupil acts a frame to which all the movements are referred. Contrary to expectation the reference plane in the eye is not the center of rotation because the movement of any opacity can be appreciated only in relation to the pupil.

  3. Opacity in fluid or solid part of the media can be differentiated by observing the after-movement of the opacity i.e. movement of the opacity after the eye has halted. Presence of after-movement denotes opacity in the fluid part of the media (aqueous or vitreous).

  4. Keratoconus gives rise to a ring-shadow corresponding to the base of the cone of the keratoconus. It occurs despite the fact that the cornea is transparent, because of total internal reflection of light occurring at the base of the cone. This reflects the light back into the eye and, thus, the base of the cone appears as a dark ring. Similar ring shadow may also be seen in lenticonus and the two can be differentiated by parallactic displacement.

  5. Iris nevus and coloboma, both of which appear as black patch on the iris, can be differentiated by DDO. Coloboma being a defect in the iris permits light to pass through it making fundal glow visible. However, glow cannot be seen across the nevus.

  6. Cataract can be easily differentiated from nuclear sclerosis which also appears gray with torch light examination. Cataract appears as dark opacity against fundal glow but in nuclear sclerosis the media are clear. Moreover, as long as some clear cortex is present in cataract some fundal glow is visible, thus differentiating immature from mature cataract. In mature cataract no glow is seen, rather pupil appears gray even with DDO due to light reflected from the cataract.

  7. Subluxation of clear lens is not obvious on examination with torch light as the pupil appears dark. With the DDO the edge of the lens crossing the pupil stand out as a dark crescent against fundal glow. Though the lens is clear yet the edge appears dark because of total internal reflection of light at lens edge.

  8. Lens Coloboma, a notch like defect in lens edge can be readily seen with DDO.

  9. Vitreous hemorrhage in its milder form gives rise to darkening of the red fundal glow which then appears deep red or maroon. In severe vitreous hemorrhage no glow can be seen and pupil appears dark as whatever light gets reflected from fundus is absorbed by the blood pigments.

  10. Retinal Detachment (RD) is separation of the neural layer of retina from the retinal pigment layer leading to loss of nutrition of the former from the choroidal vasculature. As a result of this the retina becomes grayish opaque and lies much anteriorly (closer to the lens). This gives rise to grayish glow in the area of RD and makes that part of the retina visible by DDO (detached retina becomes highly hypermetropic). Retinal folds may be seen moving with the movement of the eye and retinal vessels running over the folds as dark bands.

  11. Retinal Tumors are also visible on DDO as gray glow and sometimes the mass itself can be seen with a bunch of abnormal vessels on it. Unlike RD no folds are seen and there is no after-movement in retinal tumor.

  12. Gray glow on DDO; other causes are:

  • Fundus coloboma

  • Posterior staphyloma

  • Medullated nerve fibers in the retina (around the optic disc)

III. Indirect Ophthalmoscopy

Ophthalmoscopy means visualization of the fundus oculi. In principle, indirect ophthalmoscopy involves making the eye highly myopic by placing a high power convex lens (+13, +20 or +28 D) in front of the eye so that a real inverted image is formed in front of the lens.

Classically indirect ophthalmoscopy was done using concave mirror of the Priestly-Smith retinoscope but now it is done using a head mounted binocular indirect ophthalmoscope. Patient lies on a couch with the pupils fully dilated. The examiner stands at the head end of the bed and directs the light of the ophthalmoscope onto the patient’s eye and while looking at the pupil interposes the convex lens in front of the eye, then moving the lens away form the eye till the retina is seen clearly. A real inverted image which is 3 to 5 times magnified is formed in between the lens and the observer. The magnification depends on the power of the lens used and the refraction of the eye and is given by the refraction of the eye divided by the power of the lens used e.g. 60 D Έ 13 D = 5 approx.

Advantages

Disadvantages

1. Stereopsis: the greatest advantage is the 3 dimensional view possible with this method which lets the depth or the solid nature of a lesion to be appreciated.

2. Large field of view enables a wide area of the retina to be seen at a given time (about 30° ). Thus a large lesion e.g. retinal-detachment, tumors, etc. can be observed in its entirety.

3. Periphery of the retina can be seen, even up to ora serrata (combined with indentation of the sclera) by this method. So the peripheral retinal lesions e.g. retinal degenerations, breaks or holes etc. may be visualized.

4. Vitreous can be easily examined and various vitreous abnormalities diagnosed.

5. In hazy media this method is useful because the illumination is very bright and the method does not make use of the refractive system of the eye, thus being of immense benefit in corneal haze, cataract, vitreous hemorrhage, etc.

6. This can be used intra-operatively as there is reasonable distance between the patient and the examiner so various maneuvers can be done on the eye, and also the lens used for the purpose can be sterilized.

1. The technique is difficult to learn as the image is inverted; the orientation being achieved with lot of practice. Although by examining the patient from the head end of the bed the retina is inverted thus resulting in an ‘erect’ image yet coordinating the indentation of the sclera with the observed image requires learning.

2. It is very difficult to use this method in an upright patient.

3. The instrument is bulky and therefore not easily portable.

4. Magnification is less, therefore the small lesions e.g. macular pathology, cannot be examined in all their details.

This article is part 2 of the three article series. For rest of the parts please see the ophthalmology section of this site.



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