It is unclear why PTK was performed in Turkey. This could not be ascertained from anamnesis either. Possibly, a misdiagnosis could have let to the conduction of the PTK. Possible differential diagnoses where PTK is indicated are epithelial corneal dystrophies.
In this case, we observed a significant clinical and morphological deterioration of the disease after PTK. This was associated with an enhancement of macular corneal dystrophy lesions as proved by histopathological examinations.
In contrast, a retrospective study from 2005 reported increases of BCVA after PTK treatment in superficial corneal opacities caused by macular dystrophy. Nevertheless, the authors addressed that primary penetrating keratoplasty was still the definite therapy for this disorder .
In a study from 2006, histologic changes in corneas with macular dystrophy treated by PTK were analyzed. According to the results, the PTK treated corneas were thinner and appeared more regular than the control corneas. Also here, the authors report an accumulation of AMP-positive deposits in the PTK-treated area. After hyaluronic acid digestion, this subepithelial layer of AMP-positive substances disappeared so that the authors assume that the alterations were signs of a haze formation and not a recurrence of the macular dystrophy lesions. Transmission electron microscopy revealed more keratocytes with amorphous inclusions in the anterior stroma compared with the controls . These results are relativised by the fact that in this study only a very small number of cases of 2 eyes was examined. The authors’ conclusion contrasts with our assumption that PTK can enhance the dystrophic changes as observed in the case presented here.
In 2004, Seitz et al. suggest that due to the size and distribution of histopathologic deposits, PTK might be effective to improve visual acuity particularly in patients with granular dystrophy where deposits are located more superficial. For deeper opacities and associated thinning of the cornea, PTK does not appear as beneficial [19, 20]. Since granular corneal dystrophy belongs to the epithelial-stromal TGFBI dystrophies and deposits originate from the epithelium, it is consistent that PTK can be effective in removing the deposits especially in early stages of granular dystrophy. In more advanced stages of granular dystrophy, lesions can be distributed over all corneal layers and PTK treatment will not be sufficient.
In macular corneal dystrophy, deposits derive from and are located in the stroma. Thus, it is explainable that PTK might not be effective here.
Consistent with this, good long-term results after excimer laser PTK were observed in patients with Salzmann’s nodular degeneration, where the nodules are subepithelial or in the Bowman’s layer . In 2016, a good BCVA recovery after pannus removal combined with excimer laser PTK was observed in a retrospective study. The authors attributed this in part to a myopic shift induced by PTK in those patients . Successful treatments of recurrent erosions by excimer laser PTK have also been described in Map-Dot fingerprint dystrophy which is classified as an epithelial basement membrane dystrophy .
Interestingly, in a genotype phenotype study from 2008 where a family of macular dystrophy patients was genetically tested and different mutations of the CHST6 gene were detected, the authors suggest that therapeutic management should even depend on the particular genetic mutation. They observed that especially frameshift mutations of CHST6 cause more affected phenotypes of macular dystrophy with deeper deposits . In these cases, penetrating keratoplasty should primarily be preferred to PTK since PTK is limited to superficial corneal lesions. It must be noted that recurrences of macular corneal dystrophy are to be expected after a period of several years after penetrating keratoplasty. In patients with more superficial location of the macular deposits, PTK might be an effective primary treatment option to restore visual acuity, especially as prior PTK does not seem to influence the outcome of subsequent penetrating keratoplasty .
In conclusion, PTK can be an effective therapy in corneal dystrophies where the deposits originate from the epithelium and lesions are located superficially. However, the case presented in this report shows that macular corneal dystrophy with deeper stromal deposits should not be treated by PTK and can even lead to enhancement of the pathogenic lesions. This observation was proved by histopathologic examination of corneal tissue. Therefore, the correct diagnosis of the corneal dystrophy is crucial to guide the patient to the right therapy. In cases of macular corneal dystrophy, penetrating keratoplasty represents the gold standard and can lead to a significant BCVA improvement, even if a recurrence of the lesions is possible after years.