**6. Pattern dystrophies**

This paragraph is focused on pattern dystrophies in an attempt to offer a complete overview of OCT findings in IRD. However, in this case, the available literature is poor because of the rarity of these conditions, and in many cases, OCTA studies are completely absent.

Pattern dystrophies are a group of very rare autosomal dominant macular diseases characterized by very heterogeneous patterns of retinal pigment depositions and outer retinal alterations. Although a definite classification is still absent, pattern dystrophies are usually divided into five different categories: (I) Adult-onset foveomacular vitelliform dystrophy (AFVD); (II) Butterfly-shaped pigment dystrophy (BPD); (III) Reticular dystrophy; (IV) Multifocal Pattern Dystrophy Simulating Stargardt Disease (MPDSSD); and (V) Fundus pulverulentus [87]. However, especially looking at *PRPH2* gene variants, the clinical manifestations of pattern dystrophies may be extremely variable. In many cases, pattern dystrophies are caused by pathogenic variants of *PRPH2* gene, although other genes have been described as involved in the pathogenesis of these rare conditions. A complete noninvasive multimodal retinal imaging case diagnosed as pattern dystrophy associated with *PRPH2* gene variants is shown in **Figure 5**.

AFVD probably represents the most common pattern dystrophy, closely resembling BVMD, however is characterized by later onset, usually at 40–60 years of age. The clinical presentation is characterized by round, bilateral, symmetrical, grayishyellow, lesions within the macular area. Visual acuity is usually preserved, and electrophysiology is within normal limits. Pathogenic variants are associated with *BEST1*, *PRPH2,* or *IMPG1* genes [88, 89]. FAF is characterized by hyperautofluorescent macular lesion in the vitelliform stage; changes in FAF signals follow the progressive degeneration of the outer retina. Structural OCT shows the presence of a subretinal

*New OCT and OCTA Insights in Inherited Retinal Dystrophies DOI: http://dx.doi.org/10.5772/intechopen.109953*

#### **Figure 5.**

*Multimodal retinal imaging in PRPH2 gene-related pattern dystrophy. Confocal multicolor image (A) shows almost complete central retina atrophy. FAF image (B) confirms this finding, detecting a central mainly hypoautofluorescent signal. Structural OCT (C) shows disappeared or markedly attenuated outer retinal bands and inner retinal layers thinning. OCTA shows partially altered SCP with some segmentation and motion artifacts (D), strongly altered DCP with many projection artifacts (E), and absent central CC with exposure of choroidal vessels (F).*

vitelliform lesion very similar to the vitelliform stage of BVMD. Vitelliruptive, as well as atrophic stages, can be detected also in AFVD. The clinical course of AFVD is usually more benign than BVMD. OCTA detects flow deficits especially interesting the DCP; neovascular complications can be well-reconstructed [90].

BPD has an onset around 20–40 years of age and is characterized by bilateral accumulation of yellowish or pigmented material in a butterfly wings-like pattern at the level of the RPE; visual acuity is usually good [91]. These butterfly-like pigment changes, corresponding both to hyper- and hypoautofluorescent signals on FAF, are well-detected on structural OCT, with heterogeneous patterns of outer retinal band alterations [92]. To the best of our knowledge, no OCTA studies are available for BPD.

Reticular dystrophy is characterized by a RPE network of hyperpigmentation, resembling a fishing net, extending from the macula in all directions, with sparing of the retinal periphery in early stages. In advanced stages, this network is complicated by atrophy [92, 93].

MPDSSD shows flecks-like alterations sparse within the entire posterior pole, with atrophic changes detected in the later stages of the disease. Flecks are often localized around the vascular arcades. Fundus appearance and OCT are very similar to STGD, and the differential diagnosis is mainly based on the detection of the autosomal dominant mechanism of inheritance [94].

Fundus pulverulentus is the rarest of all pattern dystrophies and is characterized by a granular appearance with coarse and punctiform mottling of the macular RPE. The clinical presentation is quite similar to age-related macular degeneration, leading to possible diagnostic delays [95]. Choroidal neovascularization has been described as a possible complication [96].

### **7. Final remarks**

In this chapter, the most relevant OCT and OCTA findings in IRD have been described. Although several steps forward have been performed, especially looking at the most frequent IRD types, further prospective studies are needed to provide a definite categorization of each IRD and to improve the knowledge regarding the pathogenesis and the patterns of progression. Moreover, it should always be taken into account that OCT and OCTA are prone to imaging artifacts. These can be categorized as patient-related, technology-related, and disease-related artifacts [1]. Patient-related artifacts are mainly related to patients' fixation and collaboration, leading to many artifacts, including motion and blinking artifacts. Technology-related artifacts are related to the current limitation of the post-processing algorithm in carefully segmenting images and detecting signals, thus leading to biases, such as projection and segmentation artifacts. Disease-related artifacts are secondary to the disease-related alterations affecting the retinal structures, potentially masking or altering the detection of the signals. In brief, the higher are both fixation instability and pathological modifications of retinal structures, the higher will be the artifacts affecting the quality and the interpretation of OCT and OCTA images. This is particularly true for IRD, since in most of the cases, the retinal structures are remarkably impaired, and the visual function of the patients is strongly compromised. For these reasons, from one side both expert and nonexpert ophthalmologists should be familiar with imaging artifacts, to avoid misinterpretation of the findings. On the other end, further technological improvements are warranted to make noninvasive retinal imaging even more reliable for performing the diagnostic workup of IRD patients.
