Lakshmi Priya R.S, B. Optom

Aravind Fellowship in Clinical Optometry, Aravind Eye Care System, Chennai, India

As odd as it may seem, many people suffer from double vision which is when the eye perceives two images instead of one. Some of them can experience diplopia with or without any noticeable signs. Diplopia can be caused not only due to neurological problems but also due to secondary causes. When people start experiencing symptoms of double vision consistently, their life will be frustrated. It is a debilitating visual symptom so there should be an immediate intervention to correct it.

Two types of diplopia can be experienced. Monocular diplopia may be confused with the refractive blur from the patient’s perspective. This is truly experienced if double images are not completely separated. It is mostly due to post-surgical or traumatic corectopia, post refractive error surgery, irregular pupil, irregular astigmatism, comatic or higher order aberration, irregular corneal surface, keratoconus, iridotomies and dry eye syndrome. Whereas binocular diplopia needs a detailed examination (onset, quality & direction). It occurs when either eye is closed. Some of the causes are high refractive errors, nerve palsy, post brain tumour resection, post scleral buckle surgery, heterophorias, vergence insufficiency (convergence and divergence), and postoperative diplopia.

To correct diplopia, a range of different non-surgical management methods are available. One of the main optical management is the use of spectacle lenses with prisms incorporated to it. Not all of them are happy with prism glasses, as some may feel difficulties. Some factors such as cosmetically unappealing and asthenopic symptoms may restrict the use of prism glasses. For these patients contact lenses will be an ideal option.^(1-7)

Figure 1: Different types of diplopia.⁽²⁾

Wide range of contact lenses are available to correct diplopia. Soft contact lenses can be used to correct small angles of vertical diplopia. It is caused by post-surgical misplacement of a pupil or any irregular pupil, long standing diplopia one who experienced after trauma. Up to 2 prism diopters can be incorporated in the soft contact lenses.

Prosthetic contact lenses such as Type C design lenses can be used to correct the monocular diplopia. It has a small round in the centre which is the central optical media in which the light passes through. This type of CL corrects only the spherical refractive power. It is widely used in pupil abnormalities such as irregular pupil, misplacement of pupil and post-surgical anisocoria.

Figure 2: Type C contact lens with clear pupil zone and tinted iris area.

Higher order aberrations (HOA) can be reduced by using Type C lenses (i.e., pinhole soft contact lenses).In this, wide parameters are available to increase or decrease the pupil size which reduces the HOA by correcting the diplopia.

Any corneal irregularities, corneal scarring and high astigmatism that cause diplopia can be treated with Rigid Gas permeable (RGP) lens. Vertical binocular diplopia may be caused by nerve palsy or post brain tumour resection or post scleral buckling surgery. It can be treated with RGP in which the custom base down prism- ballast (about 2-4 prism dioptres) is incorporated.

Scleral contact lenses can correct diplopia caused by corneal ecstasies, post Lasik ecstasies, corneal irregularities and hypertropia. It corrects up to 5 prism diopters whereas advanced scleral lenses can correct up to 6 prism dioptres. If it is vertical diplopia, prism can be split in the eyes like half prism base up on one eye and half prism base down on other eye. It is tried when hard lenses are not tolerated. In a case reported by Vincent and fadel,⁽⁸⁾ binocular vision anomalies are corrected with the use of scleral lenses with prisms. Bragg and Sindt incorporated a base up prism of 3.5 prism dioptres with the customised scleral lens (EYE PRINT PRO) to eliminate vertical diplopia.⁽⁹⁾

CONCLUSION 

In contact lenses only a certain amount of vertical and horizontal prisms are incorporated into it. Though it is challenging, it is very effective in correcting diplopia. It has been widely used and is available to correct small angles of diplopia due to various causes and provide binocular single vision. Sheraft et al described scleral lenses without prism corrects the impaired binocularity. Vertical prisms up to 4 prism dioptres can be incorporated into a RGP lens to correct diplopia, when patients have a significant vertical phoria.⁽⁸⁾ Regular eye exams can help to identify potential eye problems like diplopia before they become more advanced. The sooner we identify, the sooner it can be treated. Contact lenses are an effective and feasible option for diplopic patients who are not satisfied with other conservative treatment options.

References

1. Robert, M. P., Bonci, F., Pandit, A., Ferguson, V., & Nachev, P. (2015). The scotogenic contact lens: a novel device for treating binocular diplopia. British Journal of Ophthalmology, 99(8), 1022-1024.
2. Double vision. (n.d.). Retrieved January 28, 2022, from https://www.snec.com.sg/patient-care/conditionstreatments/common-eye-symptoms/double-vision.
3. Alemu, H. W., & Kumar, P. (2021). Monocular Diplopia: An Optical Correction Modality. Case Reports in Ophthalmology, 12(2), 501-506.
4. Baraskar, O. R., & Gupta, O. R. (2021). Rigid Gas Permeable Contact Lenses for Irregular Corneas and High Astigmatism
5. Robert, M. P., Bonci, F., Pandit, A., Ferguson, V., & Nachev, P. (2015). The scotogenic contact lens: a novel device for treating binocular diplopia. British Journal of Ophthalmology, 99(8), 1022-1024.
6. Kalikivayi, L., Vilasendran, J. A., Lonappan, A. C., Jacob, S. C., & Kalikivayi, V. (2019). A novel method in correcting aberropia using pin hole soft contact lenses: A case report. Contact Lens and Anterior Eye, 42(3), 334-338.
7. Iliescu, D. A., Timaru, C. M., Alexe, N., Gosav, E., De Simone, A., Batras, M., & Stefan, C. (2017). Management of diplopia. Romanian journal of ophthalmology, 61(3), 166.
8. Vincent, S. J., & Fadel, D. (2019). Optical considerations for scleral contact lenses: A review. Contact Lens and Anterior Eye, 42(6), 598-613.
9. Bragg, T. L., & Sindt, C. (2015). Correction of binocular diplopia with novel contact lens technology. Journal of American Association for Pediatric Ophthalmology and Strabismus {JAAPOS}, 19(4), e38.