Rupesh Poudel (optometrist)
Diplopia is a condition where a person complains of seeing an object double. Diplopia could be monocular or binocular. Monocular diplopia may be due to repetitive images caused by cerebral polyopia or by ghosting image due to refractive errors or retinal diseases. Binocular diplopia, however, may be due to ocular misalignment or unequal image perception between two eyes. Diplopia that is perceived only occasionally is called transient diplopia that may be due to decompensated heterophoria, convergence or divergence insufficiency, spasm of accommodation or in myasthenia gravis as well. The primary goal of an optometrist in management of diplopia is to first rule out the cause of diplopia and manage accordingly.
Management of Monocular Diplopia:
Monocular diplopia may be due to astigmatism or high refractive error in people with the larger pupil. Unequal power in different meridian cause difference in image focus, thus diplopia or ghosting. Similar is the case in high refractive error with a large pupil that cause diplopia due to increased spherical aberration. The management is a refractive correction, but fine subjective refraction is of utmost importance and doesn’t forget JCC refinement as even small axis misalignment of correcting cylinder may cause shadowing of the image. High corneal irregularity though may not be compensated by spectacles alone, thus, this is where need for Rigid Gas permeable (RGP) arises. Diplopia after PK or any other corneal refractive surgery may often require RGP contact lens with a large diameter. In cases with physiologically mid dilated pupil but have a high refractive error, go for aspheric lenses or coloured contact lenses with clear pupil. Cause like dry eye can be better managed with appropriate tear substitute or other treatment modality. Although, severe dry eye conditions may even call for mini scleral or scleral contact lens wear.
Management of binocular diplopia
Anisometropia is a condition where there is a difference in power of two eyes. Binocular single vision works best when image formed in two eyes are similar in nature. When best glasses correction between two eyes differs by significant amount, there is difference in image size also (anisekonia) and hence our brain is unable to perceive those image as a single object, thus causing diplopia. Better go for contact lens in these cases, as anisekonia becomes negligible. What about unilateral progressive myopia in children, “yes there is another option not just to treat anisometropia but to halt unilateral progression”, called orthokeratology, that uses ortho-k RGP lenses with special reverse geometry design and yield reverse fitting outcome (i.e central bearing with mid peripheral clearance) to aid epithelial cell migration which is the main basis of orthokeratology. This causes central flattening of corneal curvature.
Heterophoria simply means latent deviation, where our eyes have tendency to deviate from normal alignment (orthophoric) condition, but is in control due to our motor fusion capability. When our motor fusion capability is not always able to align the eyes anymore, it is called decompensated heterophoria. It may exhibit intermittent exotropia or esotropia leading to an intermittent type of diplopia. Management of such cases is done by vision therapy or prism prescription. Always go for vision therapy first, prism prescription is for those who are reluctant to vision therapy or those whose decompensation is too frequent and is in urgent need for diplopia correction. We don’t want prism prescription in initial stages as the patient may adapt to the prism( prism adaptation) and the symptoms might recur even with prisms. In intermittent exotropia, overcorrect minus prescription and give positive fusional vergence exercise. In intermittent esotropia, overcorrect plus and give negative fusional vergence exercise. Remember office vision therapy is best as it has a high rate of compliance and examiner can assess condition frequently. Prism prescription is based on phoria and fusional vergence reserve. In exodeviation use sheard’s criteria and in esodeviation use Percival crieteria for prescribing prism.
Sheard’s crieteria ( Base in prism)
Prism value is : 2/3rd (Demand)-1/3rd (Reserve)
Demand is = Phoria value, Reserve is = Base out blur value
Percival’s crieteria ( Base out prism)
Prism value is: 1/3(BO blur) -2/3(BI blur)
Always prescribe prisms equally in both eyes.
Most common cause of acute decrease in vision with diplopia involving accommodative dysfunction is pseudomyopia, which most of the time present with acute esotropia. Dry retinoscopy reveals low to high degree of myopia(may be as high as -10D) but on wet retinoscopy the objective value is zero or negligible. It may be due to abnormal convergence-accommodation synkinesis or psychogenically induced. Whatever the cause may be, our goal is to relax accommodation. Small degree of pseudomyopia in near workers may be treated with low power plus lenses. Pseudomyopia of higher degree needs cycloplegic therapy. Cyclopentolate (05.% TID) or (1% BD) for three weeks can be given along with near addition glasses during the drug course.
Convergence insufficiency is a commonly encountered problem in clinics and hospitals. Normally our eyes are able to converge at a pointsnearer than 10 cm from eyes. But inability to converge over large distance may cause diplopia at near. The first approach in managing the problem is home based and office based fusional vergence exercise. But, symptomatic relief can be brought about by the use of base In prisms. Prisms along with vision therapy would be a good idea in vergence dysfunction.
In paralytic strabismus the main step of management is to wait and watch for diplopia to resolve. Till then go for patching, frosted lens or contact lens with black pupil. Binasal frosting of lens is also an option to prevent diplopia at particular gaze. If the deviation remains same during subsequent follow ups we can go for prism priscription. The prism priscription doesn’t follow sheards or percivals criteria here. Just try to give least prism value (that is less than actual primary ocular deviation) which corrects diplopia in primary gaze. Obviously, the person’s diplopia won’t be corrected in the gazes towards paralytic muscle side. If you are enthusiastic and your patient is complaint enough, why not go for vision therapy. Monocular vision therapy can be advised in those patients. The main goal for vision therapy is to strengthen the paralytic muscle. Vertical diplopia is a bit problematic, but small vertical deviation may do well with prisms. In presbyopes, with vertical diplopia, one better option can be monovision contact lens. Alternate suppression for far and near vision in one and other eye help in overcoming diplopia in some population.
Diplopia is called intractable when it cannot be corrected by vision therapy, prisms, surgery or any other means. The only choice that remains for management of such cases is occlusion of one eye. Are we going to patch eye or use contact lens with black pupil ? No, not yet we should not go for complete occlusion in intial stage because we will be blocking the form sense of the patient. Patient must at least be able to sense what is going in his other eye’s visual field i.e. visual sense of periphery. So, give frosted lens or you can frost only 1 cm circular zone at the center of the lens. Still reluctant!, what about fogging with high power or using special type of lens called Chavasse lens. Diplopia in children younger than 9 yrs of age should be advised for alternate patching because of risk of developing occlusion amblyopia.
Prisms: A Handy Armor
(Grounded prisms/Fresnel prisms)
Grounded prisms are those that are grounded over current glass prescription. Due to the cosmetic appearance and heaviness of lens the maximum prism value grounded is upto 10-12 Prism Diopters only (in Nepal prescribe upto 8 PD) in a single lens of a glasses, thus 8+8 equals 16 PD in total. Prism prescription above that value can be given Fresnel prism. Fresnel prism comes as a sheet ranging value from 1 to 40 PD. It comes in a shape like lens blank, that can be cut according to lens size and pasted over back of the lens after little wetting with water in adhesive side.
We give therapy/prescription to avoid diplopia but does any condition arise where we actually need to create diplopia?
Yes, in stoke patient with prolonged ischemia, a part of brain function decreases and there occurs visual neglect. Visual agnosia, a term where a person sees object in his visual field but fails to recognize them as brain tries to neglect the percept. In those patients, the prism is prescribed to create diplopia, hence awareness of objects in field of vision.
(Note: In a stroke patient, usually when right brain lobe is affected in right-handed person or left-brain lobe affected in left-handed person, hemiagnosia may occur, where a person neglects sensation in one half of the body, including visual field neglect even though there is no true loss of sensation.)
Summary of management of diplopia
- Refractive correction ( glasses / contact lens)
- Appropriate Vision therapy ( exercises)
- Use of prisms
Summary of some cases with diplopia:
Case 1: A 19-year-old female patient came to our clinic with chief complain of intermittent diplopia. On investigation, her general ocular health was normal. She had no refractive error with 6/6 vision in each eye. But, on orthoptics examination it was revealed that she had intermittent esotropia. Her esotropia was of around 15 PD. Her positive fusional vergence break value was over 30 PD for far and 35 PD for near. Her negative fusional vergence break value was 4 PD for distance and 6 PD at near. She was advised for divergence exercise on synaptophore but she couldn’t fuse the target at zero vergence position of the machine fusional target. Then the fusional target in one of the eye was moved towards examiner until patient reported seeing two fusional targets as single. It was at 15 PD eso movement of target at which machine was locked. The exercise was advised to prevent fused target from separating while rotating drum towards abduction. After 3 weeks of exercise, every 6 days a week, she could fuse target upto zero vergence position of the synaptophore target on abduction. Her diplopia problem was totally eliminated. She is still doing exercise as maintenance therapy for about 3 times a week.
Case 2: An 11-year-old boy came to the clinic with chief complain of double vision since 1 month. His general ocular health was normal. On refraction, his refractive error was -7.25 Diopters in right eye and -8.00/-0.25×15 in left eye. On orthoptics examination it was found that he had esotropia of 6 PD both for distance and near.Refraction was then carried out under cyclopentolate 1% and was found to be -0.50/-0.25×90 in right eye and -0.50 Diopters in the left eye. The patient was diagnosed of pseudomyopia. He was advised for cyclopentolate 1% BD for 3 weeks, along with near glasses of +2.50 Dsph during the drug course. On the follow up visit after stopping the drop, his eye was evaluated again. He had 6/6 vision in both of his eyes with no esotropia or any complain of double vision. (Case seen by Hira Nath Dahal, optometrist , Dristi Eye Clinic)
Case 3: An 18-year-old male came to our clinic with a chief complain of diplopia at distance. His presenting visual acuity with glasses was 6/9 in each eye. His refractive error was +10 Diopters in each eye, similar to current glasses. He had 20 PD esophoria at near and 14 PD esotropia at distance. The plan was made to decenter the lens to relieve the symptoms. The goal was to create 14 PD of Base In decentration. So, using prentice rule (prism= power X decentration in cm) i.e (14= 10 X Decentration), hence total decentration needed was found to be 1.4 cm base In, which was divided as 7.5 mm temporal decentration in each eye. The diplopia was eliminated with and the patient had improved positive and negative fusional vergence with decentered glasses.
Fig: Frosted Lens
Rupesh Poudel (optometrist)
Tilganga Institute of Ophthalmology