Presentation
Patient AA (age 56) presented to our clinic complaining of fluctuating vision throughout the day which he had first noticed some two years ago. A number of eye tests were performed by different practitioners over the subsequent few months, the results of which were significantly different.
Relevant history
The patient had undergone radial keratotomy in 1986 to correct myopia. The pre-operative refraction had been:
R: -3.50 DS
L: -3.00 DS.
Post-operative refractions had varied considerably.
Action taken
To investigate the symptoms, we decided to proceed with phasing, repeated measurements of ocular parameters over a set period of time. The patient was seen at six different times during the same day, with the first measurements taken at 08:00 and the last at 21:00. During each visit we measured the following:
- Refractive error
- Corneal topography
- Intraocular pressure (IOP)
- Central corneal thickness (CCT).
Table 1: Summary of results for right eye
Results
We discovered the patient had a flattened cornea upon waking which became gradually steeper over the course of the day. This resulted in a myopic shift of -2.50DS in the right eye and -1.75 DS in the left over a period of 12 hours.
Table 2: Summary of results for left eye
The change in corneal power corresponded with the change in refraction. There were no significant changes found in IOP and CCT. Since this assessment, the patient has been similarly assessed several times, each time showing similar and repeatable results. Table 1 summarises the results of the right eye phasing (see figures 1 to 5), and table 2 the results for the left eye (figures 6 to 9).
Figure 1: Corneal topography for each eye at (a) 08.00, (b) 10.45, (c) 13.40, (d) 17.45, (e) 19.35, (f) 21.05
Conclusion
Our hypothesis was that the weakened cornea for each eye was being flattened by the lid during sleep, and this was followed by a rebound effect upon waking and over the course of the following day. This theory is also supported by the fact that, when the patient sleeps during the day, the same pattern reoccurs. The patient was offered the option of corneal cross linking as a means of stabilizing the cornea, but he rejected this option for the time being. After discussing possible contact lens and spectacle options, we decided to proceed with multiple pairs of spectacles to be worn as appropriate.
Guide to submission
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Christos Papageorgiou is a UK qualified optometrist currently in practice in Greece.